UNIVERSITY GHENT
UNIVERSITEIT GENT
INTERUNIVERSITY PROGRAMME MASTER OF SCIENCE IN PHYSICAL LAND RESOURCES Universiteit Gent Vrije Universiteit Brussel Belgium
Stabilization of soils from Cameroon for construction purposes
September 2006
Promotor: Prof. J. Wastiels Advisor: Dr. Mazen Y. M. Alshaaer
Master dissertation in partial fulfilment of the requirements for the Degree of Master of Science in Physical Land Resources by: Ndofor Akongnui Fai
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Abstract Local soils are the most common, easily available and cheap construction materials used for simple structures in most parts of Cameroon. Due to their poor durability, severe limitations have been unraveled while using these soils. Various techniques have been used over the years to improve on the durability of these soils. The possibilities of using the mineral polymerization (MIP) technique for the stabilization of kaolinitic soils with the aim of making them more suitable for construction purposes was investigated using four soil samples ( FET, FBM, FNB, and FNK) from Cameroon. This technique is based on the micro structural transformation of some clay minerals into solid and stable materials having hydroxysodalite, feldspatiod or zeolite characteristics under the action of alkaline reactants, at atmospheric pressure and low (quasi environmental) temperatures. Granulometric analysis, plasticity and loss on ignition tests were used to characterize the soil samples. They all had the required amount of kaolinite; averagely 40%. Adding 12% sodium hydroxide at optimum water and sand content to sample FNK, compressive strengths which meet the requirements for construction materials precursors were obtained. These strengths were 25MPa and 10MPa under dried and immersed conditions respectively. Sample FBM also gave acceptable compressive strengths by adding 8% sodium hydroxide at optimum water and sand content to the sample which were 12MPa and 7MPa under dried and immersed conditions respectively. Despite all efforts, we were unable to obtain acceptable compressive strengths for the FET and FNB samples probably due to the presence in the samples of other kinds of clays or colloidal materials which are undesirable for the technique. With a soil sample that meets the requirements for this technique, optimizing the quantity of various constituents results in very good mechanical and physical characteristics of the resulting construction materials. The smaller the grain sizes used, the more the properties of the materials are improved as there will be a larger surface area for reactions to occur. Ideal curing temperatures lie between 75°C and 85°C as higher temperatures only increase cost and pollution with no considerable improvement in the mechanical and physical properties of the materials. Ndofor Akongnui Fai
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ii The mineral polymerization technique can be considered as a potential technique for the improvement of some soils in Cameroon for it is cheaper, environmentally friendlier than traditional methods and produces strong and durable construction materials.
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Acknowledgements The scientific journey that has produced this thesis has seen the contribution of seasoned scientists, institutions, family and friends. Without them, I wonder whether this adventure of mine would have yielded any fruits. I am most grateful and will be eternally indebted to my thesis promoter Prof. Dr. Ir. Jan Wastiels and advisor Dr. Mazen Alshaaer. Their patience and invaluable guidance has been the main driving force behind this work. Words cannot express what I have learnt from them within and outside this research. I will also like to express my gratitude to the academic and administrative staff of the Physical Land Resources Programme in the University of Ghent and the Vrije Universitiet Brussels under the leaderships of Prof. Dr. E. Van Ranst and Prof. Dr. F. De Smedt respectively. Their guidance and assistance has been of much help and value to this work. Special thanks go to Dr. Uphie Melo Chinje the director of the Local materials promotion authority (MIPROMALO) Cameroon who assisted me immensely in sample collection. By granting me access to the library and laboratories of her institution under the supervision of her assistants, the fieldwork and collection of samples for this work saw the light of day. The mind searching discussions and exchanges we had on the subject were also enriching. Thank you once more madam. I acknowledge the warmth of my course mates throughout the two years. My cluster friends Lambive, Messiga, Uzoma, Prabin, Lee and Nawal have been exceptional “we remain united”. Hearty thanks go to my mum and dad Helen Nkeh and William Nkeh respectively for their support and love through out my educational ladder. I will always remain indebted to them reason why l dedicate this work to them. I am equally grateful to my sisters and brother, Relindis, Jacqueline, Loveline, Mary, Therese and Julius. I wish to thank all my friends and most especially, Eric Andangfung who inspired me into the field of engineering geology. I am particularly thankful to Ursula for her last minute support. Her support, understanding, and advice helped me to courageously surmount all difficulties provoked by my long absence from home. Finally I would like to thank all the good people at the Vlaamse Interuniversitaire Raad (VLIR) and the Flemish Government for financing my studies.
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Table of Content Abstract ...................................................................................................................................... i Acknowledgements................................................................................................................... iii Table of Content ....................................................................................................................... iv List of Figures........................................................................................................................... vi List of Tables .......................................................................................................................... viii Chapter-1 General Introduction ............................................................................................1 1.1 General Background ....................................................................................................1 1.2 The use of soils for construction materials in Cameroon ..............................................1 1.3 Problem Description ....................................................................................................2 1.4 Objectives....................................................................................................................3 Chapter-2 Literature Review ................................................................................................4 2.1 Improvement of Soils for Construction ........................................................................4 2.1.1 Mechanical Stabilization ......................................................................................4 2.1.2 Physical Techniques.............................................................................................5 2.1.3 Physico-chemical techniques – fired bricks ..........................................................6 2.1.4 Chemical Stabilization .........................................................................................7 2.2 Clay Minerals and other silicate minerals in soils.........................................................9 2.3 Chemistry of Inorganic Polymers...............................................................................15 2.4 Mineral Polymerization Technique ............................................................................16 Chapter-3 Area Description ................................................................................................22 3.1 Introduction ...............................................................................................................22 3.2 Collection of Samples................................................................................................22 3.3 The Yaoundé area deposits ........................................................................................24 3.3.1 Nkolbison sample ..............................................................................................24 3.3.2 Mvog Betsi sample ............................................................................................24 3.3.3 Simbock sample.................................................................................................25 3.3.4 Parent material for Yaoundé soils.......................................................................25 3.4 Bambili Sample .........................................................................................................25 Chapter-4 Characteristics of Soil Samples ..........................................................................27 4.1 Introduction ...............................................................................................................27 4.2 Moisture Content .......................................................................................................27 4.3 Grain Size Distribution ..............................................................................................28 4.4 Atterberg Limits ........................................................................................................31 4.5 Plasticity Index (PI) ...................................................................................................32 4.6 Loss on Ignition.........................................................................................................33 Chapter-5 Methodology......................................................................................................38 5.1 Materials....................................................................................................................38 5.2 Fabrication of Specimens...........................................................................................38 5.2.1 Mixing ...............................................................................................................39 5.2.2 Moulding ...........................................................................................................39 5.2.3 Curing................................................................................................................40 5.2.4 Post curing and Pre-test Treatments ...................................................................40 5.3 Measurements............................................................................................................40 5.4 Testing.......................................................................................................................41 5.4.1 Uniaxial Compression test..................................................................................41 Ndofor Akongnui Fai
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v 5.4.2 Loss of compressive strength .............................................................................42 5.5 Water Absorption ......................................................................................................42 5.6 Efflorescence and pH.................................................................................................42 5.7 Homogeneity of the mixture ......................................................................................43 5.8 Checking the effect of maximum grain size of soil samples .......................................43 5.9 Checking the effect of curing temperature..................................................................43 5.10 Improving specimen’s characteristics using sodium hydroxide ..................................43 Chapter-6 Observations, Results and Discussions ...............................................................44 6.1 Mvog Betsi sample, (FET).........................................................................................44 6.1.1 Fabrication of Specimens ...................................................................................44 6.1.2 Physical Characteristics of Specimens................................................................45 6.1.3 Compressive strength and Stability ....................................................................50 6.1.4 Efflorescence .....................................................................................................53 6.2 Bambili sample, (FBM) .............................................................................................53 6.2.1 Fabrication of specimens....................................................................................54 6.2.2 Physical Characteristics of Specimens................................................................54 6.2.3 Compressive strength and stability .....................................................................59 6.2.4 Efflorescence .....................................................................................................62 6.2.5 NaOH as stabilizing argent.................................................................................63 6.3 Simbock sample, (FNB).............................................................................................64 6.3.1 Fabrication of Specimens ...................................................................................64 6.3.2 Physical Characteristics of Specimens................................................................65 6.3.3 Compressive strength and stability .....................................................................70 6.3.4 Efflorescence .....................................................................................................73 6.4 Nkolbison sample, (FNK) ..........................................................................................73 6.4.1 Fabrication of Specimens ...................................................................................74 6.4.2 Physical Characteristics of Specimens................................................................75 6.4.3 Compressive strength and stability .....................................................................79 6.4.4 Efflorescence .....................................................................................................82 6.5 Changing the maximum grain size of soil samples .....................................................83 6.5.1 Physical Characteristics of Specimens................................................................83 6.5.2 Compressive strength and Stability ....................................................................85 6.6 Influence of curing temperature .................................................................................86 6.6.1 Influence of curing temperature on density.........................................................86 6.6.2 Compressive strength and stability .....................................................................87 Chapter-7 Conclusions and Recommendations ...................................................................89 7.1 Specifications for the use of soils in construction .......................................................89 7.2 Mvog Betsi sample, (FET).........................................................................................90 7.3 Bambili sample, (FBM) .............................................................................................90 7.4 Simbock sample, (FNB).............................................................................................91 7.5 Nkolbison sample, (FNK) ..........................................................................................91 7.6 Changing the maximum grain size of soil samples .....................................................92 7.7 Influence of curing temperature .................................................................................92 7.8 Sodium hydroxide as stabilizing argent......................................................................92 7.9 Recommendations .....................................................................................................93 References ................................................................................................................................94
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List of Figures Figure 1, Basic structural unit of silicates [21]...........................................................................10 Figure 2, Linking of (SiO4)-4 tetrahedra to form silicates............................................................10 Figure 3, An exploded view of the aluminum octahedral unit [21].............................................12 Figure 4, Structure of gibbsite [21]............................................................................................12 Figure 5, Structure of kaolinite..................................................................................................13 Figure 6: Sketch picture of kaolinite structure showing distances between atoms ......................15 Figure 7, General formulas of polysiloxanes (1) and polyphosphazenes (2)...............................16 Figure 8, Hydrosodalite unit cell, [(Si-O-Al-O), nNa, nH2O] (Source : S. Kowalak et al, (Modified 2000)).......................................................................................................................18 Figure 9, Schema showing reaction between Kaolinite and NaOH.............................................19 Figure 10, Map of Cameroon showing sampling locations.........................................................23 Figure 11, Grain size distribution curve and summary of other properties - FET........................29 Figure 12, Grain size distribution curve and summary of other properties - FBM ......................30 Figure 13, Grain size distribution curve and summary of other properties – FNB ......................30 Figure 14, Grain size distribution curve and summary of other properties – FNK ......................31 Figure 15, An illustration of boundaries between Atterberg’s limits ..........................................31 Figure 16, Incremental loss on ignition at various temperatures - FET.......................................34 Figure 17, Total loss in weight at various temperatures - FET ...................................................34 Figure 18, Incremental loss on ignition at various temperatures – FBM.....................................35 Figure 19, Total loss in weight at various temperatures – FBM .................................................35 Figure 20, Incremental loss on ignition at various temperatures – FNK .....................................36 Figure 21, Total loss in weight at various temperatures – FNK..................................................36 Figure 22, Incremental loss on ignition at various temperatures – FNB .....................................37 Figure 23, Total loss in weight at various temperatures - FNB...................................................37 Figure 24, Variation of density with % NaOH – FET ................................................................47 Figure 25, Variation of density with water content – FET..........................................................47 Figure 26, Variation of density with sand content - FET............................................................48 Figure 27, Variation of water absorption with NaOH content - FET ..........................................49 Figure 28, Variation of water absorption with water content - FET............................................49 Figure 29, Variation of water absorption with sand content – FET.............................................50 Figure 30, Variation of compressive strength with water content – FET ....................................51 Figure 31, Variation of compressive strength and NaOH content – FET ....................................52 Figure 32, Variation of compressive strength with sand content – FET......................................53 Figure 33, Variation of density with NaOH content – FBM.......................................................55 Figure 34, Variation of density with water content- FBM ..........................................................56 Figure 35, Variation of density with sand content – FBM..........................................................57 Figure 36, Variation of water absorption with NaOH content – FBM ........................................58 Figure 37, Variation of water absorption with water content - FBM ..........................................58 Figure 38, Variation of water absorption with sand content - FBM............................................59 Figure 39, Variation of compressive strength with NaOH content - FBM ..................................60 Figure 40, Variation of compressive strength with water content - FBM....................................61 Figure 41, Variation of compressive strength with sand content – FBM ....................................62 Figure 42, Stabilization potentials of NaOH - FBM...................................................................64 Figure 43, Variation of density with NaOH content – FNB........................................................66 Figure 44, Variation of density with water content - FNB..........................................................67 Ndofor Akongnui Fai
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vii Figure 45, Variation of density with sand content - FNB ...........................................................68 Figure 46, Variation of water absorption with NaOH - content ..................................................69 Figure 47, Variation of water absorption with water content - FNB ...........................................69 Figure 48, Variation of water absorption with sand content – FNB............................................70 Figure 49, Variation of compressive strength with NaOH content – FNB ..................................71 Figure 50, Variation of compressive strength with water content – FNB....................................72 Figure 51, Variation of compressive strength with sand content – FNB .....................................72 Figure 52, Variation of density with NaOH content – FNK .......................................................75 Figure 53, Variation of density with water content – FNK.........................................................76 Figure 54, Variation of density with sand content - FNK ...........................................................77 Figure 55, Variation of water absorption with NaOH content - FNK .........................................78 Figure 56, Variation of water absorption with water content - FNK...........................................78 Figure 57, Variation of water absorption with sand content – FNK............................................79 Figure 58, Variation of compressive strength with NaOH content – FNK..................................80 Figure 59, Variation of compressive strength with water content - FNK ....................................81 Figure 60, Variation of compressive strength with sand content – FNK.....................................82 Figure 61, Variation of density with grain size – FBM ..............................................................84 Figure 62, Variation of water absorption with grain size – FBM................................................85 Figure 63, Variation of compressive strength with grain size – FBM.........................................86 Figure 64, Variation of density with curing temperature - FBM.................................................87 Figure 65, Variation of compressive strength with curing temperature – FBM...........................88
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List of Tables Table 1, Main types of silicates .................................................................................................11 Table 2, Geographical location of sampling sites.......................................................................24 Table 3, Hygroscopic moisture content of samples ....................................................................28 Table 4, Atterberg limits and Plasticity indices for the various samples .....................................33 Table 5, Composition of each series of specimens - FET ...........................................................44 Table 6, Variation of density with NaOH content - FET ............................................................46 Table 7, Variation of density with water content - FET .............................................................46 Table 8, Variation of density with sand content - FET ...............................................................46 Table 9, Variation of water absorption with NaOH content - FET .............................................48 Table 10, Variation of water absorption with water content - FET .............................................49 Table 11, Variation of water absorption with sand content - FET ..............................................50 Table 12, Variation of compressive strength with water content - FET ......................................51 Table 13, Variation of compressive strength with NaOH content - FET.....................................52 Table 14, Variation of compressive strength with sand content - FET........................................52 Table 15, Composition of each series of specimens - FBM........................................................54 Table 16, Variation in density with NaOH content - FBM .........................................................55 Table 17, Variation of density with water content - FBM ..........................................................56 Table 18, Variation of density with sand content - FBM............................................................56 Table 19, Variation of water absorption with NaOH content - FBM ..........................................57 Table 20, Variation of water absorption with water content - FBM............................................58 Table 21, Variation of water absorption with sand content - FBM .............................................59 Table 22, Variation of Compressive strength with NaOH content - FBM ..................................60 Table 23, Variation of compressive strength with water content - FBM.....................................61 Table 24, Variation of compressive strength with sand content - FBM ......................................61 Table 25, Effects of NaOH on compressive strength - FBM ......................................................63 Table 26, Composition of each series of specimens - FNB ........................................................64 Table 27, Variation of density with NaOH content - FNB .........................................................66 Table 28, Variation of density with water content - FNB ...........................................................66 Table 29, Variation of density with sand content - FNB ............................................................67 Table 30, Variation of water absorption with NaOH content - FNB...........................................68 Table 31, Variation of water absorption with water content - FNB ............................................69 Table 32, Variation of water absorption with sand content - FNB..............................................70 Table 33, Variation of compressive strength with NaOH content - FNB ....................................71 Table 34, Variation of compressive strength with water content - FNB .....................................71 Table 35, Variation of compressive strength with sand content - FNB .......................................72 Table 36, Composition for each series of specimens - FNK.......................................................74 Table 37, Variation of density with NaOH content - FNK .........................................................75 Table 38, Variation of density with water content - FNK...........................................................76 Table 39, Variation of density with sand content - FNK ............................................................77 Table 40, Variation of water absorption with NaOH content - FNK...........................................77 Table 41, Variation of water absorption with water content - FNK ............................................78 Table 42, Variation of water absorption with sand content - FNK..............................................79 Table 43, Variation of compressive strength with NaOH content - FNK....................................80 Table 44, Variation of compressive strength with water content - FNK .....................................81 Table 45, Variation of compressive strength with sand content - FNK.......................................81 Ndofor Akongnui Fai
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ix Table 46, Variation of density with grain size - FBM ................................................................83 Table 47, Variation of water absorption with grain size - FBM..................................................84 Table 48, Variation of compressive strength with grain size - FBM...........................................85 Table 49, Variation of density with curing temperature - FBM ..................................................87 Table 50, Variation of compressive strength with curing temperature - FBM ............................87
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Chapter-1
General Introduction
1.1 General Background Cameroon is highly under-developed, with poverty, poor healthcare, malnutrition, poor road infrastructure, and poor housing conditions being very prominent. The use of cheap and high quality local natural resources for construction purposes is therefore very vital for its sustainable development. With very low purchasing powers, very few Cameroonians can afford for conventional building materials which entail a lot of money to buy and transport them to construction sites. However, Cameroon is potentially provided as far as natural construction materials are concern. Their advantages are increasing from the scientific, economical and environmental points of view. Qualitative and quantitative data on these materials are not yet sufficient for their valorization. Knowledge of the benefits and usefulness of natural resources, how people used them in the past and how they are using them now for construction is very vital in order to boost development in Cameroon. To gain this knowledge, an assessment of the geotechnical properties of materials and various methods that have been used or maybe used to improve upon these properties is necessary.
1.2 The use of soils for construction materials in Cameroon One of the demands of rising populations and rising standards of living is the increasing use of resources for construction. As a result, some construction resources such as soils, which rarely possess the characteristics of volume stability, strength and durability required in construction, have to be used. In order to use these materials and come out with good results, there is the need for their improvement.
The improvement of these materials is termed stabilization. Soil
stabilization can be described as the modification of soils to meet specific engineering requirements. Soil stabilization is commonly used to describe any physical, chemical or biological method or combination of such methods used to improve certain properties of a natural soil for intended purpose. The use of conventional construction materials requires a high level of technical know how. In Cameroon, well trained technicians who can easily apply these methods are rare and expensive to pay for by an average citizen. Cheap and easy to use naturally
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2 occurring local materials which require simple and cheap techniques to improve upon their properties will therefore be of great necessity and advantage. It is rather unfortunate that in Cameroon a greater majority of the population uses basic earth materials without any modification on their properties for construction. Most buildings built with only basic earth materials suffer relatively rapid deterioration due to low dry strengths which decrease to zero under wet conditions and also have high porosities and water absorption. They also show the development of shrinkage cracks under dry conditions, swelling under wet conditions and a generally high susceptibility to damage due to periodic wetting and drying.
1.3 Problem Description Modern construction materials are accompanied by a lot of energy consumption and environmental degradation. The high cost of energy and transportation has made the prices of cement and its related products beyond the rich of most Cameroonians. The first stage of all industrialization, and increasing standards of living, requires concrete for building infrastructures. The manufacture of traditional Portland cement requires calcining calcium carbonate. This yields calcium oxide and carbon dioxide gas. The emission of carbon dioxide is therefore, becoming a growing concern; it is an important contributor to the green house effect. As regards development statistics, the worldwide level of cement production is expected to be 3.5 billion tons by the year 2015. This would put the share in the global pollution (all human activities combined) at 18% [1]. Most specifications used in tropical countries were developed to meet the needs of the temperate climatic conditions of Europe and North America and do not seem to recognize the special characteristics of tropical soils.
In Cameroon, much still has to be done to adapt these
specifications to local realities, especially as the country has a varied surface geology. Most of the specifications in use are those borrowed from France. Modifications to existing specifications, taking into account the peculiarities of local soils are indeed necessary if they are to be used effectively. An elaborate study of the properties of the natural construction materials and ways of improving on their properties in all parts of Cameroon so as to come out with specifications that will reflect local climatic and environmental conditions is of great necessity. Ndofor Akongnui Fai
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This study is going to evaluate the potentials of the Mineral polymerization (MIP) Technique which has been well studied in the Mechanics of materials and construction laboratory of the Vrije Universiteit Brussel at solving one of these problems. This technique of soil stabilization is not well known in Cameroon though soils suitable for the technique are likely quite abundant given the local climatic conditions and geology. With this technique, stone-like materials are produced from kaolinitic soils at atmospheric pressures and low temperatures. This requires less equipment and is less expensive to produce and also more environmentally friendly since rapid deforestation due to utilization of wood for energy and the emission of large quantities of carbon dioxide to the atmosphere will be greatly reduced. The products of this technique can be used as structural materials with attractive properties in construction and other applications.
1.4 Objectives Based on the problems outlined above, four soil samples were collected from Cameroon, whose quality and suitability for construction purposes will be evaluated using the Mineral Polymerization (MIP) technique. We aim at producing high quality and durable construction materials using an environmentally friendly and easy to apply technique at low cost. Secondly, different relationships between materials compositions and manufacturing processes, physical and mechanical properties and durability of the materials produced will be assessed.
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4
Chapter-2
Literature Review
2.1 Improvement of Soils for Construction The most common soils which are used for construction in Cameroon are lateritic soils. In regions where it is available and cheap, wood is commonly used but its greatest short coming is its low durability since it is hardly seasoned and treated to fight against insect attacks and humidity. Lateritic soils are the products of the intensive weathering that occur as a result of the tropical and sub-tropical climatic conditions in this country. These soils are generally rich in secondary oxides and sesquioxides of iron and/or aluminum. They are nearly devoid of bases and primary silicates but may contain large amounts of secondary quartz and kaolinite. [2] The most common and simplest process for the manufacturing of bricks from lateritic soils in most countries in Africa consists in taking these soils and drying them in open-air [3]. Given the nature of the type of soils found in this region, it is rather difficult to manufacture bricks by the traditional process of firing at high temperature around 900°C to 1100°C. Bricks manufactured simply by mixing the soils with water and drying in open-air have not been able to give good results in terms of dimensional stability, strength, stiffness, permeability and durability. With these problems encountered, there is thus a need to look for means of improving these soils. Efforts have been made of recent towards this and results have shown that blocks and bricks made from lateritic soils can be improved to produce masonry units with strengths high enough to meet building standards [4]. 2.1.1
Mechanical Stabilization
Mechanical stabilization is a very commonly used technique in Cameroon especially in road construction, where lateritic soils are used for sub-base and base course. This involves decreasing of the soil voids by mechanical means so as to increase the density and strength, and to achieve a decrease in compressibility, permeability and porosity [5]. Laboratory analysis on the soils is carried out in order to determine optimum conditions before this method is applied. The parameters mostly analyzed are the grain size range and optimum moisture content that will
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5 give high density values after compaction. These laboratory analyses already constitute a limitation to average Cameroonians. Even with a proper application of this method, long-term problems still occur. The improved physical contact between the soil grains leads to an increase in strength and a reduction in porosity, which in turn leads to some reduction in water absorption and migration. Even though initial strength may be high, long-term stability cannot be assured. The improvement in physical strength alone is not enough to ensure that the ingress of water is significantly reduced on a longterm or permanent basis [5]. This short coming has been observed in many roads in Cameroon which gave good results at the time they were constructed. 2.1.2
Physical Techniques
Additional fines or aggregates maybe blended into a material to adjust its granulometric composition before compacting. This will result in a uniform, well graded, dense soil-aggregate mixture after compaction [6]. Various means of defining the assortment of sizes required to achieve the maximum density have been devised, of which the most common is to regard the material as a selection of spheres of decreasing size such that [7]: p=P
d D
n
…………………. (1)
Where p is the proportion of spheres smaller than d in diameter, P is the proportion of spheres smaller than D in diameter and n is the grading coefficient (D>d). For maximum density, n ranges from 0.33 to 0.5 This is a very cheap and easy to apply method, e.g. the use of sand in stabilizing fine grained soils rich in clays will lead to a decrease in their degree of plasticity and swelling. Using this method, lateritic soils in Kumasi Ghana were blended with alluvial gravel and this resulted in a more remarkable improvement in the particle size distribution with the resulting mixture producing strength gain and markedly enhanced material quality [8]. Four day soaked CBR values of at least 80% could be achieved in the laboratory for some of the blended specimens compared to about 46% for the unblended specimens. These blending techniques are very popular in Cameroon especially for road construction. A typical example where this was applied Ndofor Akongnui Fai
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6 is the Yaoundé-Nsimalen-Mbalmayo road which was constructed in 2003 with the base course made of lateritic soils (75%) blended with crushed rocks (25%) of diameter 0-25mm. Based on the specifications in use, very good results were obtained (Razel Cameroun,2003). Soil reinforcement by incorporating components such as fibers, electrical or electro-osmosis treatment and the use of sand drains are other physical techniques which can be used to improve upon the properties of soils [5]. These methods require a lot of technical know how and money and are not commonly used in Cameroon. 2.1.3
Physico-chemical techniques – fired bricks
These techniques use a combination of both physical and chemical methods. A typical example is firing of bricks. When bricks are fired, the actual reactions which enable a suitable product to be formed are chemical while the heating itself is a physical process. Some people refer to this as thermal stabilization. Though sun-dried bricks are the most popular, heat stabilized bricks are also widely used in Cameroon. The technique of making fired bricks requires a lot of experience and knowledge. The problem of cost of energy and controlling baking temperatures has lead to a lot of research. This motivated Mbumbia et al [9] who worked on lateritic soils from Cameroon and found out that it is possible to produce strong bricks at lower temperatures without additives, simply by crushing the raw materials to obtain medium to fine particles. However the means to crush is a limitation to the average Cameroonian. Chinje and Monget [10] also tried to solve this problem of cost of energy. They constructed a traditional down-draught wood fired kiln for firing tests of clay bricks through which they discovered that massive dry wood gave better results than wet wood which is mostly used by local producers. They also discovered that adding saw dust of <12% to body composition reduced drying times and improved the mechanical properties of the final products but raised porosity. In an effort to lower production cost, the effects of fluxes on the temperature at which fired clay bricks mature have also been studied [11]. It has also been found that just the energy needed accounts for about 30% of the cost of production [9], and this has resulted in the firing technique not widely used in Cameroon. Ndofor Akongnui Fai
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7 2.1.4
Chemical Stabilization
Chemical stabilization techniques rely on the use of admixtures to alter the chemical properties of the soil in order to achieve desired effects [6]. Chemical stabilization includes the use of chemicals and emulsions as compaction aids to soils, as binders and water repellants and as a means of modifying the behavior of clays [12]. Physical stabilization techniques are the cheaper and easier to use techniques but when they do not offer good results, geotextiles or chemical admixture stabilization is the final solution. To carry out any chemical stabilization, the raw material properties have to be determined and suitable chemicals selected based on the available financial resources. 2.1.4.1 Lime stabilization There is evidence that lime (Ca(OH)) was used in Roman times for the stabilization of roads in areas with smectitic soils. Lime produces a dramatic decrease in the plasticity index (Liquid limit – Plastic limit); first by increasing the plastic limit and secondly by producing hydrated Ca-Al silicate cementing agents which bind the clay particles together [13]. When lime is added to a clay soil, it has an immediate effect on the properties of the soil as cation exchange begins to take place between the metallic ions associated with surfaces of the clay particles and the calcium ions of the lime. Clay particles are surrounded by a diffuse hydrous double layer which is modified by the ion exchange of calcium. This alters the density of the electrical charge around the clay particles which leads to them being attracted closer to each other to form flocs, the process being termed flocculation. It is this process which is primarily responsible for the modification of the engineering properties of clay soils when they are treated with lime [14]. Many of the engineering properties of clay soils are enhanced by the addition of lime. These properties vary and depend upon the character of the clay soil, the type and length of curing and the method and quality of construction [15]. The largest increases in plastic limits are observed in montmorillonitic clays, while for kaolinitic clays the change is small. The liquid limit for kaolinitic clays is increased while for montmorillonitic clays it is reduced. Therefore montmorillonitic clays respond more rapidly to lime stabilization and so exhibit earlier gains in strength than do kaolinitic clays. However, after further ageing the additional strength achieved
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8 by montmorillonitic clays is not as high as that achieved by kaolinitic clays [15]. However, the optimum addition of lime needed for maximum modification of the soil is normally between 1% and 3% lime by weight and further additions of lime do not bring changes in the plastic limit but increase the strength. A reduction of the swell percent and swell pressure of clay soils to zero with additions of 6% lime has also been reported [16]. Hence the quantity of lime to be added for a specific soil should be determined from laboratory test and analysis on samples. The most important beneficial effects of lime stabilization on soils include; the broadening of the range of moisture tolerance of the soil, the reduction of the soil plasticity, the increase in the strength and fair improvements of volume stability by reductions in shrinkage and swelling [5]. 2.1.4.2 Cement stabilization Cement can be used as an effective stabilizer for a wide range of materials. Portland cement can be used both to modify and improve the quality of a soil or to transform the soil into a cemented mass which significantly increases its strength and durability, with the amount of cement additive depending on whether the soil is to be modified or stabilized [6]. The amount should be determined in the laboratory by varying the proportions of cement-soil mixtures and testing their properties and the proportion which offers the properties which meet specifications selected. Unlike in lime stabilization, the chemical reaction takes place in the cement rather than the soil. Hydration reactions in cement lead to the formation of calcium silicate hydrates which bind soil grains together [17]. Clay masses containing more than 5% montmorillonite are hardly stabilized with economically justifiable amounts of cement. This can be explained by the fact that the Ca2+ ions of the cement are adsorbed by montmorillonite preventing the hydration of cement and also montmorillonite is very susceptible in contact with water because of its expansive property. Comparing the performances of lime and cement as modifiers for laterites with immediate and time effects taken into consideration, results show marginally better performances for lime with respect to both effects [18]. Cement stabilization is quite popular in the road construction sector in Cameroon. Lateritic soils are stabilized with cement and used for the base course of paved roads. The results obtained so far have been quite good based on the specifications in use and their durability. With the high cost of cement and the technical know how required, this method has not been very popular in Cameroon for building construction.
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9 2.1.4.3 Stabilization using organic compounds Large organic cations have been found to produce decreases in the expansive properties of soils. Bitumen, asphalt and tars are the most common organic soil stabilizers. Cut backs and emulsions are commonly used though emulsions are preferred over cutbacks because of energy constraints and pollution control effects. In the case of cut backs (Kerosene + tar), kerosene evaporates when the cut back is spread on the soil while for emulsions (water + tar), water evaporates during curing. The tar left on the soil forms a water resistant binder between its grains. Water absorption is greatly limited as the tar acts as a waterproof. This leads to improvements in strength and volume stability (reduced expansion) of the soils.
2.2 Clay Minerals and other silicate minerals in soils To better understand the engineering properties of soils, a profound knowledge of the minerals that make up these soils is important. Amongst the minerals which make up soils, clay minerals are the most abundant. The physical and chemical characteristics of soil minerals are very important in considerations in planning, constructing and maintaining buildings, roads and airports. Clays are naturally occurring materials formed by the weathering and decomposition of igneous rocks [19]. These layered materials fall under the group of phyllosilicates that are themselves part of the silicate mineral class. Clays are materials based on a two-dimensional stack of inorganic layers. The layers are made of either tetrahedral sheets of SiO2 motifs or octahedral sheets of metal oxide and hydroxide (where the metal can be Al, Fe, or Mg) or both. Cohesion between the layers is maintained by weak electrostatic and Van der Waals interactions mediated by interlayer cations and water molecules [20]. Like in all silicate minerals, in phyllosilicates, the (SiO4)-4 tetrahedron is the most basic structural unit. The SiO44- tetrahedral structure is shown in figure 1 below. The shape of a silicate anion is a tetrahedron, not a sphere like a simple anion. The Si-O bond is approximately 50% covalent and 50% ionic, that is, although the bond arises in part from the attraction of oppositely charged ions, it also involves sharing of the electrons and inter-penetration of the electronic structure. The Ndofor Akongnui Fai
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10 total bonding energy of Si+4 is distributed equally among 4 O-2 ions; hence, the strength of any Si-O bond is equal to 2 the total bonding energy in the O-2 ion. Therefore each O-2 has the potential of bonding to another (SiO4)-4 group and entering into another tetrahedral grouping. The uniting of the tetrahedral groups leads to sharing or bridging O-2 ions, and hence, polymerization. However, you never get more than one O-2 being shared between two silica tetrahedra. . Figure 2, illustrates how different tetrahedral are linked to each other to produce phyllosilicates.
Figure 1, Basic structural unit of silicates [21]
Figure 2, Linking of (SiO4)-4 tetrahedra to form silicates
Silicate minerals are classified on the basis of the degree of polymerization of the (SiO4)-4 tetrahedra and this results in 6 main types of silicates. The main types of silicates are grouped in table 1 based on the number of bridging oxygens (#BO) per (SiO4)-4 tetrahedron
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11 Table 1, Main types of silicates
The Si - O combination has a radius ratio of 0.30, which means that the silicon ion fits nicely into a tetrahedral polyhedron. This gives the orthosilicate anion, which could at least theoretically be neutralized by four protons (hydrogen ions). This anion tends to react readily with alkali and alkali earth ions. If each of the four oxygen ions bond with two silicon ions the result is a quartz crystal. In phyllosilicates, only one plane of oxygen ions bond with two silicon ions. This bonding is extended in two directions to form a sheet of silicon tetrahedrons [21]. The second basic building block of the phyllosilicates is an aluminum octahedral unit. The aluminum/oxygen radius ratio is 0.41, which falls at the maximum ratio for tetrahedral coordination and minimum ratio for octahedral coordination. Depending on conditions, aluminum can coordinate with either four or six oxygen ions. As it turns out, however, within the phyllosilicate mineral structure the aluminum ion is "more comfortable" in an octahedral coordination. An exploded view of the aluminum octahedral is shown in figure 3. Using the same simplified approach that we used to explain the SiO44- tetrahedral unit, aluminum might be said to share +0.5 of its charge with each of the surrounding oxygen ions, leaving each oxygen ion with a negative 1.5 charge. This excess negative charge on the oxygen ions needs to Ndofor Akongnui Fai
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12 be balanced and the charge can at least be partially balance if each oxygen ion is bonded with two aluminum ions. Once again, this could theoretically happen by the three face oxygen ions, the two edge oxygen ions, or the single corner oxygen ion bonding with two Al ions. In this case aluminum is slightly less electropositive than is silicon and is able to approach close enough that corner oxygen ions can be shared. In a matrix of these octahedral units each oxygen will be bonded to two aluminum ions, leaving it with a remaining -1 charge. The charge can be satisfied by attaching a proton (hydrogen ion) as shown in figure 4. When this type of structure is continued in three dimensions we have the mineral GIBBSITE [21].
Figure 3, An exploded view of the aluminum octahedral unit [21]
Figure 4, Structure of gibbsite [21]
We have another option for balancing the remaining -1 charge on the oxygen ions. In the sheet of silicon tetrahedral units, apical oxygen ions still have an unbalanced charge. The two sheets can be brought together with the apical oxygen ions of the tetrahedral layer also being in the octahedral layer. As a result, the charge on these oxygen ions is balanced by bonding to one silicon ion and two aluminum ions. This is the basic structure of our first phyllosilicate mineral, Ndofor Akongnui Fai
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13 KAOLINITE. Its structure is illustrated in figure 5. It is about 0.7 to 0.74 nm thick (from the bottom oxygen to the top oxygen) and extends 10 nm and more in the other two directions [21].
Figure 5, Structure of kaolinite We can speak of this three dimensional structure as a clay micelle. The kaolinite mineral is actually made up of many micelles piled one atop the other. Since the surface on one micelle contains hydrogen ions and the other surface only oxygen ions there is a tendency for hydrogen bonds to form between micelles. While individual hydrogen bonds are very low energy, the bonding energy is additive and the sum of the many hydrogen bonds between micelles results in the micelles being very strongly bonded together and nearly impossible to separate. Thus, we speak of kaolinite as being a nonexpanding phyllosilicate. Since each micelle is constructed of a layer of silicon tetrahedral units and a layer of octahedral units, kaolinite is called a 1:1 clay mineral. Thus, kaolinite is a 1:1 nonexpanding clay mineral. The composition of kaolinite is very constant, without any isomorphic substitution either in the tetrahedral or the octahedral sheet. This absence of isomorphic substitution is the cause that no charge is present on the lattice [13]. Since we replaced the hydrogen ion on one layer of octahedral oxygen ions by a silicon ion it is only logical that the remainder of the hydrogen ions can be similarly replaced. This results in another class of clay minerals the 2:1 clay minerals. These minerals consist of two silicon tetrahedral layers and one aluminum octahedral layer e.g. smectites and micas [21]. In this work, kaolinite will be used as a precursor for construction materials. In contrast to the 2:1 clay
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14 minerals, it is characterized by a good dimensional stability, low plasticity and doesn’t swell when saturated with water. It retains its white color when fired. In general Kaolinite is an inorganic polymer, with its backbone chain made up of silicon and aluminum atoms. It is generally formed in soils as a result of the chemical weathering of feldspars (equation 2) and other clay minerals like illite (equation 3) and smectites. 2KAlSi3O8 + 9H2O + 2H+
Al2Si2O5(OH)4 + 2K+ + 4H2 SiO4 ------ (2)
(K-feldspar)
(Kaolinite)
2KAl2(AlSi3)O10(OH)2 + 5H2O (Illite)
3Al2Si2O5(OH)4 + 2KOH ------ (3) (Kaolinite)
When kaolinite is heated to temperatures of about 500 to 600°C, the water that was chemically bound to it is lost leading to a highly disordered structure (metakaolinite) as shown in the figure 6 below. This loss on ignition could be related to the amount of kaolinite present in a soil sample. For it has been shown that normally about 13.95% the initial weight of kaolinite is lost when it is heated to temperatures between 450 and 550°C which corresponds to the weight of water lost. This is the technique we have used in this work to determine the quantity of kaolinite in the soil samples. The dehydroxylation process of kaolinite leading to the formation of metakaolinite at 500-600°C (depending on the degree of structural disorder) can be expressed as in equation 4. Al2(OH)4Si2O5
Al2Si2O7+ 2H2O ………………. (4)
The rupture of the kaolinite framework and transformation into metakaolinite induces a sharp modification of the intra-cell geometry with an abrupt modification of the Si-O, Al-O, Al-Si distances (distances labeled as 1, 2, and 3 in the sketch picture of kaolinite in Figure 6). When the dehydroxylation reaction is completed metakaolinite is reorganized and shows a larger degree of long-range order compared to the intermediate reaction products [22]. When heating is continued to about 900°C, metakaolinite transforms into a short-range ordered material with a mullite-like structure, which is completely anhydrous. This is made up of 3 phases; mullite, -alumina and silica, according to the reaction shown in equation 5. 3Al2Si2O7
Al4SiO8 + Al2O3 + 5SiO2. ..................... (5)
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15
Figure 6: Sketch picture of kaolinite structure showing distances between atoms
2.3 Chemistry of Inorganic Polymers Inorganic polymers are a group of compounds containing non-carbon elements as the principal backbone, where the variation in the side groups attached to the inorganic backbones yields polymers with a great range of properties. Broadly, the inorganic polymers we will deal with in this work may be considered as three-dimensional framework aluminosilicates consisting of corner-sharing silicate and aluminate tetrahedra, containing metal cations which balance the negative charge of the aluminate groups. They are typically made with compositions (in terms of oxides) of approximately M2O·3SiO2·Al2O3·12H2O, where M is an alkali metal cation (usually Na or K) [23]. These polymers can be tailored for a variety of applications, including ceramic precursors, electronic materials, nonlinear optical materials, and biomedical materials [24]. Inorganic polymers set and harden in a physically similar process to Portland cement and have potentially similar applications. Inorganic polymers may also have applications in toxic waste stabilization, advance composites and as cement additives [25, 26, and 27]. Despite having cost, environmental and performance advantages over current binder technologies, the great potentials of inorganic polymers are only now being realized. This has been mainly attributed to the fact that there has been little fundamental research into the relationships between empirical
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16 formulations of inorganic polymers and their chemistry, structure and performance characteristics [23]. The two largest classes of polymers with inorganic backbones are the polysiloxanes (silicones) and the polyphosphazenes, whose general formulas are shown in figure 7 below.
Figure 7, General formulas of polysiloxanes (1) and polyphosphazenes (2)
Polysiloxanes were first prepared on a laboratory scale by Kipping in England in the early 1930s, and were developed as useful polymers in the late 1930s and 1940s in the United States by Hyde at the Corning Company, by Rochow, Pattnode and Gilliam at the General Electric Company, McGregor at the Mellon Institute, and by scientists at Union Carbide. Similar developments were also reported in Russia [28]. The bond between silicon and oxygen is very strong, but very flexible. So silicones can stand high temperatures without decomposing, but they have very low glass transition temperatures. Like the polysiloxanes, polyphosphazenes are made of alternating atoms; in this case, the chain is made up of alternating phosphorus and nitrogen atoms. Compared with most organic polymers, inorganic polymers are generally stronger, harder, more brittle and usually insoluble. They do not burn (with few exceptions) and only soften or melt at very high temperatures.
2.4 Mineral Polymerization Technique Mineral polymerization (MIP) has been defined as the micro structural transformation of clay minerals into a tectosilicate structure under the action of alkaline reactants, at atmospheric pressure and low (quasi environmental) temperatures [29]. When added to an appropriate soil, sodium hydroxide reacts with kaolinite which has a sheet-like (2 dimensional) structure and transforms it to a more stable 3 dimensional (tectosilicate) zeolite or feldspathoid structure at temperatures below 100°C. Stone like shaped objects can thus be Ndofor Akongnui Fai
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17 made which are stable in water and are high temperature resistant. If there is the need, fine and clean sands are also added to the mixture to improve upon the granulometry of the resulting material and thus improve on the strength and durability. Mineral polymers have also been widely referred to as geopolymers [30]. Over the years there has been great improvement over the development of new materials based on mineral (geo) polymerization. Davidovits [30] describes the reactions which lead to the formation of these new materials as reactions which involve the chemical reaction of alumino-silicate oxides (AL3+in four fold coordination) with alkali polysilicates yielding polymeric Si-O-Al bonds; with the amorphous to semi-crystalline three dimensional silico-aluminate structures being of the poly(sialate) type (-Si-O-Al-O-), the poly(sialate-siloxo) type (-Si-O-Al-O-Si-O-) and the poly(sialate-disiloxo) type (-Si-O-Al-O-Si-O-Si-O-). Some early workers discovered that when sodium hydroxide is added to kaolinite, it attacks the clay mineral lattice and this result in the formation of sodium silicate and sodium aluminate, with the latter proceeding to precipitate insoluble aluminum oxide hydrates, which give the soil considerable durability [7, 31]. As we saw before, Kaolinite is an inorganic polymer, with its backbone chain made up of silicon and aluminum atoms. It is generally formed in soils as a result of the chemical weathering of feldspars (equation 2) and other clay minerals like illite (equation 3) and smectites. The composition of kaolinite is very constant without any isomorphic substitution either in the tetrahedral sheet or in the octahedral sheet. Hence no permanent charge is present on the lattice. Charges can thus only arise from broken bonds on the edges of the mineral. Exchange of H+ ions at the edges of kaolinite clay mineral for Na+ ions seem to be the most likely initial reaction when sodium hydroxide is added to kaolinite [32]. This leads to dispersion of clay particles because of the repulsion between the Na+ ions which have large radii. This results in sodium silicate and sodium aluminate and possibly other sodium compounds. By adding sodium hydroxide to Kaolinite, we thus in principle reverse equation (2) whereby the 2-dimensional network polymer is transformed into a 3-dimensional frame-work polymer which is harder and more stable (equation 6).
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18 Si2O5Al2(OH)4 + 2NaOH (Kaolinite)
Na2Si2Al2O8.3H2O -----(6) (Hydrosodalite)
The new mineral formed from this reaction has a zeolitic structure as illustrated in figure 8.
Figure 8, Hydrosodalite unit cell, [(Si-O-Al-O), nNa, nH2O] (Source : S. Kowalak et al, (Modified 2000))
Not all soils are suitable for this technique. The soils most contain a reasonable amount of kaolinite which is the main precursor mineral for the important chemical reactions, with the other clay minerals present only in small amounts or absent [29]. For this reason, sedimentary clays which contain swelling clays should be avoided as these clays do not take part in the reaction and so retain their normal undesirable characteristics in the resulting product. The presence of non clay minerals is acceptable. Laboratory analysis most therefore be carried out to determine the mineralogical composition and the properties of the soil sample before they can be used. Wastiels (2001) came out with the requirements for the mineralogical composition and physical properties of soils, which are summarized below. 1.) Mineralogical composition -
Kaolinite must be present; (a minimum of 20% of total soil mass) although lower amounts maybe acceptable in some cases.
-
Other clay minerals than kaolinite should be avoided as much as possible, especially the swelling clays like smectites, only a few percent are tolerable.
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19 -
Non-clay minerals can be present e.g. quartz and feldspar. Most crystalline alluminosilicates are acceptable and even useful. Carbonates and iron oxides are acceptable.
-
Organic compounds are to be avoided.
-
Components not stable in strongly alkaline conditions should be avoided e.g. amorphous silica, microcrystalline silicates, sulphates etc.
2.) Physical Properties -
Particles with a grain size larger than 5mm have to be sieved out.
-
Minimum clay content should be 10%, with ideal clay contents being 20–30%
-
The ideal overall granulometric curve is broad and regular, between clay and coarse sand size, with clay size fraction consisting of kaolinite.
-
Following the standard Atterberg limit test, a classification as CL or ML of the fraction <450 microns is advisable.
It was shown that with the precursor mineral kaolinite, adding sodium hydroxide to it will yield sodalite based Na-poly(sialate) (Si2O4,Al2O4,2Na),3H2O within 20 seconds time at temperatures of 150°C and pressures of 5-10MPa [30]. This is illustrated in the schema in figure 9 below.
Figure 9, Schema showing reaction between Kaolinite and NaOH
The inorganic polymerization technique therefore results in the formation of amorphous or micro-crystalline equivalents of some synthetic zeolites. These are more stable and have higher strengths than the precursor clay minerals and so will result in far better construction materials.
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20 It is based on the above reactions that new materials have been produced which have replaced some traditional materials that were organic in origin and had a lot of short comings. These materials have lead to applications in the construction industry (bricks, tiles, fire resistant chipboard panels, cement), used as binders, fire resistant and heat resistant fiber composites, sealants for industry, tooling for aeronautics, radioactive and toxic waste encapsulation, etc. [33]. Instead of using kaolinite as the precursor, metakaolin has also been widely used with very encouraging results obtained [23]. However the recent trend has been to use fly ash as the precursor for the reactions [34]. Fly ash being an industrial waste has an advantage over metakaolin. It is a waste resource produced in huge quantities by coal-fired power stations, making it an ideal environmentally friendly feedstock. It consists of fine, amorphous and reactive aluminosilicate particles. Class F fly ash, which is high in aluminosilicate and low in calcium, is the preferred grade for inorganic polymerization. Fly ash is far less pure than metakaolin, but produce more complex inorganic polymer structures [34]. Effects of other types of alkali apart from sodium hydroxide and their concentrations have also been investigated, with the most popular being potassium hydroxide [23, 34]. These works showed that metakaolin or fly ash is more soluble in sodium hydroxide than in potassium hydroxide, because products using the latter contained more un-reacted particles than those using the former. The sodium based inorganic polymer was also found to be stronger than its potassium based equivalent. So sodium hydroxide is preferred over potassium hydroxide for the making of construction materials. The stabilization of kaolinitic clays from Suriname using the MIP technique resulted in a remarkable improvement of the strength in both dried and immersed specimens. For the dried specimens, the improvement in strength was 8 to 53 times that of the unstabilized soil [35]. Brownish-red portions of soils from the Al-Mudawwara deposit in Southern Jordan have also been stabilized using this technique and it was discovered that low priced, stable, reliable and high quality construction materials with maximum compressive strengths of 22MPa and 50MPa tested under wet and dried conditions respectively by using 6% sodium hydroxide were obtained [36]. Testing Kaolinitic clays from Vietnam stabilized using this technique, it was concluded that clay from the Huu Khanh kaolin mine satisfies the criteria to be used as precursors of low priced,
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21 stable, reliable and high quality construction materials, with maximum compressive strengths of 12.78MPa and 34.00MPa tested under wet and dried conditions respectively [37]. The stabilizing effects of alkaline additives have also been investigated using latosols from Ghana and very god results obtained [5]. These results attest to the fact that with the MIP technique, it is possible to produce building materials whose properties can be compared to those of more traditional materials like baked bricks or concrete blocks. The amount of sodium hydroxide added depending on the soil, i.e. not fixed. These materials are cheaper and environmentally friendlier than their traditional equivalents due to the lower amount of energy they need for their processing.
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22
Chapter-3
Area Description
3.1 Introduction Cameroon is located in West – Central Africa. It has a total area of about 475440km2 comprising 469440km2 land and 6000km2 water. It has boundaries with The Central African Republic, Chad, The Republic of Congo, Equatorial Guinea, Gabon, and Nigeria. The country has a coastline along the Atlantic of about 402km.The Climate varies with terrain from tropical along the coastal area, to semi arid in the north. The topography is varied with plains in the east, south and southwest, dissected plateaus in the centre, mountains in the west, southwest and northwest and plains in the north. Altitudes range from zero meters along the coast to about 4095 m above sea level on mount Cameroon which is the highest mountain in West Africa and an active volcano. The country has a population of about 17 million, with a growth rate of about 1.97% (2005 est.).
3.2 Collection of Samples With the help of the Director and staff of the Local Materials Promotion Authority (MIPROMALO) in Cameroon, we used the guide on suitable samples for the MIP technique (Wastiels (2001) [29]) to help us in sample collection. MIPROMALO is a research institute under the ministry of scientific research in Cameroon which has as one of its main functions, the identification of potential local construction materials. This was the main reason why l solicited their help since obviously they possess data that could serve as a guide in selecting potential sampling sites. Like in most under-developed countries, this research institute lacks modern equipment and has very few researchers. The data available there was not quite sufficient to help us determine with certainty what will eventually give the expected results. There were some documents (unpublished) containing data about the mineralogical and chemical composition of soils around Yaoundé in particular and the country in general. Most of the data was too general and incomplete. There was also no possibility of carrying out some tests in order to help us determine the mineralogical and chemical composition of samples. Three sampling sites were selected around Yaoundé which is the capital of Cameroon and another site selected in Bambili, which is a small village about 15km from Bamenda the capital of the North West province. Figure 10 shows the location of the sampling sites in Cameroon.
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23 Figure 10, Map of Cameroon showing sampling locations
Location of Bambili
YAOUNDE SHOWING SAMPLING LOCATIONS
Sampling Locations Ndofor Akongnui Fai
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24
3.3 The Yaoundé area deposits Three sampling sites were chosen around Yaoundé. This was based on data obtained from MIPROMALO and works by Liboum et al [11]. The sites chosen were at Nkolbison, Mvog Betsi and Simbock. Table 2 below presents the location of all four sampling sites obtained using a GPS. Table 2, Geographical location of sampling sites
3.3.1
Site
Symbol
Geographic Coordinates (DMS)
Elevation above sea level
Nkolbison
FNK
E011°25.197 N03°52.597
2401ft (732m)
Mvog Betsi
FET
E011°29.085 N03°52.147
2428ft (740.54m)
Simbock
FNB
E011°28.176 N03°48.986
2297ft (700.58m)
Bambili
FBM
E010°15.011 N05°58.600
5872ft (1791m)
Nkolbison sample
The sample was collected from a clay deposit which had just been discovered by MIPROMALO some few months before. Soils collected from this deposit were being tested for the eventual manufacture of baked bricks. While data on its mineralogical and chemical composition was not available, the results of the L.O.I test proved that the clay deposit was rich in kaolinite. The soils have cream colored portions mixed with reddish portions (pepper and salt). The deposit covers a vast area of about 3 hectares and has a depth of about 6m. The topography is rugged, and where the sample was collected at a depth of 1.5m, there is a slope of about 2%. 3.3.2
Mvog Betsi sample
Soils from this deposit are being used by MIPROMALO for the making of baked bricks and cement stabilized bricks. MIPROMALO carried out a geotechnical identification of the soils. Analysis carried out by Liboum et al [11] could justify our sampling from this area. He reported the presence of a reasonable amount of kaolinite and a deficiency in the swelling clays. The deposit covers a very wide area of about 20 hectares and the sample was collected at a depth of 4m. The site has a rugged topography, and is covered by short trees and grass. The soils are reddish in color, indicating they are rich in iron oxides and sesquioxides.
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25 3.3.3
Simbock sample
We collected samples from Simbock also based on the findings of Liboum et al [11]. The deposit is being exploited for road construction in Yaoundé. The area is covered by forest and grass. The sample was collected at a depth of 2m. These soils are yellowish in color. 3.3.4
Parent material for Yaoundé soils
The rocks which underlie the soils in Yaoundé are commonly referred to as the Neoproterozoic Yaoundé “series”. The Yaoundé “series” is an association of metasedimentary (garnet-kyanite, garnet-plagioclase and amphibole-biotite gneisses and micaschists) and metaplutonic (mostly garnet-pyroxene metadiorites) rocks that underwent a regional metamorphism culminating in the granulite facies. The deformation is polyphase, the latest stage corresponding to the southward thrusting of the unit onto the Congo craton. Except for the metamorphism which is well constrained at ca. 620 Ma, the deposition age of the package is still uncertain, but is assumed to be younger than 1.0 Ga. TDM ages of most of the rocks indicate a mixed source between Paleoproterozoic and Neoproterozoic components. The question still debated is the tectonic position of the “series” (autochthonous or allochthonous on the craton) and the tectonic significance of granulitic rocks (root of a collision zone or intracontinental). These rocks are naturally very rich in feldspars and quartz. Given that this area is found in the tropical rain forest of Africa, climatic conditions greatly favor intense weathering. The intense weathering is responsible for the accumulation of thick layers of soils on these rocks. From equation (2), chemical weathering of feldspars will result in the production of kaolinite, reason why the soils are very rich in kaolinite. Given the nature of the terrain at the locations where we collected the samples, the swelling clays which are mostly sedimentary in origin should be very minute in the samples.
3.4 Bambili Sample Bambili is a small village about 15km from Bamenda the North West provincial Capital. It is located in the West Cameroon Highlands between the Bamenda Plateau and the Bambutos Mountains. Average air temperatures are about 21–24 °C throughout the year. Most precipitation falls between June and October. The West Cameroon Highlands range up to 4,000 m elevation in
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26 the Adamawa and Bamenda Plateau regions. Highland vegetation includes cloud forest, riparian forest, and extensive montane grasslands, such as the Bamenda Grass fields. The Bamenda Highlands are predominantly grass-covered, with gallery forest persisting in steep valley sides or gullies. Local geology is dominated by granitic and volcanic rocks of probable Tertiary age and numerous maars and crater lakes of indeterminate age mark the landscape. The sample was collected not far from the Bamenda-kumbo highway, where there is a huge kaolin-rich soil deposit. It has a cream-white color and looks hard but easily crumbles when squeezed with the fingers. The deposit is being tested for the manufacturing of roofing tiles. The parent rocks are rhyolites of Tertiary age. These rhylolites mostly occur in the form of tors, commonly referred to as the Bambili tors. They are acid volcanic rocks, thus are very rich in quartz and feldspars. Weathering of these feldspars over the years has given rise to soils very rich in kaolinite according to equation 2. Swelling clays are almost absent given the nature of the terrain from where the sample was collected. The terrain is very highly rugged with steep slopes giving no room for sedimentary clays to be formed.
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27
Chapter-4
Characteristics of Soil Samples
4.1 Introduction In order to carry out any successful stabilization on a particular soil, we should first of all identify and classify the type of soil we are dealing with. This is because not all soils are suitable for all techniques. For this work, the guide for the general characteristics of suitable soils for the MIP technique mentioned in the previous chapter was used to decide on what to sample [29]. The geotechnical properties of the samples were determined in the laboratory to further confirm our choices. An understanding of these geotechnical properties was also necessary in order to optimize the soil/sand/water/NaOH ratios. The following aspects were determined in the Laboratory; liquid limit, plastic limit, plasticity index, moisture content, particle size distribution, loss on ignition and organic matter content. The moisture contents and plastic limits served as a guide for us to determine the optimum water contents that will result in the best densities and strengths for the materials after stabilization The particle size distribution is important when we have to optimize soil/sand ratio in order to achieve good physical stability. The loss on ignition helped us to estimate the amount of kaolinite present in each soil sample.
4.2 Moisture Content The moisture content, which is attributed to the unbonded water in the soil samples, was determined. Moisture content is the ratio of the weight of water to the weight of solids in a given volume of soil. The moisture content of a sample is an indication of how stable the soil is with respect to strength and compressibility. Samples with very high moisture contents may undergo large volume changes in response to applied loads. Also, soils with high moisture contents tend to be quite weak. The consistency of soils may be very soft or very hard depending upon their mineralogical and water contents. Between these extremes, the soil may be molded and formed without cracking or rupturing the soil mass. The hygroscopic moisture content was that which was determined. To determine the hygroscopic moisture content of a soil, a weighed amount of the soil which was first dried at room temperature was put in an oven set at a temperature of 105°C. After drying, the sample was removed and weighed. The difference between the initial weight and the weight after drying the sample, gave the weight of unbonded water in the sample. Ndofor Akongnui Fai
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28 The natural moisture content is given by the ratio of the weight of water and that of the dry soil. This is expressed as a percentage, see table 3 below for the hygroscopic moisture contents of the various samples. Table 3, Hygroscopic moisture content of samples
Soil Sample Bambili (FBM) Mvog Betsi (FET) Simbock (FNB) Nkolbison (FNK)
Hygroscopic water content (%) 4.98 2.86 5.57 2.62
4.3 Grain Size Distribution The grain-size distribution expresses the percent of the sediment mass that is finer than a given grain size. This was determined for each of the samples by carrying out a sieve analysis using standardized sieves and sedimentation using a hydrometer. The results were then represented on a chart from which we could determine if the sample is well graded (size of the particles being distributed over a wide range of sizes), uniformly graded (the size of particles being distributed over a narrow range of sizes) or gap graded (several distinct size ranges occurring within a sample). In order to reduce cost of transportation, the soil samples from the Yaoundé area were dried in the sun and sieved with a sieve having openings of 5mm. Only the portions <5mm in diameter was brought to Belgium since for the work, large grain sizes are undesirable. In the Mechanics of Materials and Construction (MEMC) laboratory of VUB, a weighed amount of each sample was used for grain size analysis using sieves with standardized openings. The portion for each sample that was below 2mm was then separated. On this portion, wet sieving was carried out using a 75 m sieve. The fraction >75 m was then dried in an oven set at 105°C and after drying it was sieved using sieves with their openings ranging from 850 m to 75 m. For the fraction <75 m, a sedimentation test was performed by means of a hydrometer using sodium hexametaphosphate as dispersing argent. The hydrometer method is based on Stokes'Law which indicates that a larger grain size will result in a larger terminal velocity when dropping through a fluid (i.e. the larger size reaches the bottom quicker, assuming uniform density). The percent by weight of soil passing each opening was then plotted as a function of the grain diameter Ndofor Akongnui Fai
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29 (corresponding to a sieve number). The horizontal scale on this plot is logarithmic. Figures 11 to 14 show grain size distribution curves for the very fine grains and a summary of the Atterberg limits, organic matter content and plasticity indices for various samples. From these curves, we can estimate the quantity of grains <1µm in the fine portion of each soil sample. FET is made up of about 40%, FBM about 20%, FNB about 58% and FNK about 50% of grains <1µm. Therefore apart from FBM, the other three samples have very important amounts of grains <1µm which is an indication of the presence of finer minerals than kaolinite. These finer minerals could possibly be smectites or colloidal materials which are undesirable for the MIP technique.
Figure 11, Grain size distribution curve and summary of other properties - FET
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30
Figure 12, Grain size distribution curve and summary of other properties - FBM
Figure 13, Grain size distribution curve and summary of other properties – FNB
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31
Figure 14, Grain size distribution curve and summary of other properties – FNK
4.4 Atterberg Limits Most soil classification systems used in construction classify soils based upon grain-size distribution and Atterberg limits. These limits divide four different "states" of consistency. If a soil is heavily saturated with water and then is dried out, it will move from a liquid state to a plastic state to a semisolid state and then to a solid state. The dividing line between the liquid and plastic states is the liquid limit (LL). The dividing line between the plastic and semisolid states is the plastic limit (PL). And the dividing line between the semisolid and solid state is the shrinkage limit (SL). These boundaries are illustrated in figure 15.
Figure 15, An illustration of boundaries between Atterberg’s limits
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32 The values of these limits are affected by the interaction of the soil particles and the water present in the sample. Because other properties such as compressibility or permeability depend on the interaction of soil particles and water, the Atterberg limits can be related to these other properties. For this work, the liquid and plastic limits were determined, for they are those necessary. Most commonly Liquid Limit and Plastic Limit are an integral part of several engineering classification systems to characterize soils. Although these limits represent water content, they are expressed without the percent designation. The liquid limit is determined based on the number of blows required to cause a groove to close in a sample. This is determined using the apparatus of Casagrande. It is a brass cup with a cranking arrangement by means of which the cup can be lifted and dropped under standardized conditions. The soil was first dried and sieved and only the fraction <425 m used. About 200g of the sample was soaked with distilled water and left for about 24hours. After ripening, the sample was then spread on a porcelain plate with distilled water added if it was too dry. After homogenizing, the soil was evenly spread out in the cup and a grooving tool used to make a 40mm long and 2mm wide groove which divides the sample in the cup into 2 equal parts. The cup was then lifted and dropped until the groove closed. The number of times N the cup was dropped was noted.
A small amount of the sample was taken and its moisture content
determined. The remaining sample was then put back on the porcelain plate and the process continued until we had about 4 values which occur at different moisture contents. Using semilogarithmic paper, water content was plotted against log N. The water content corresponding with N equals 25 is the liquid limit. The plastic limit is determined as the water content at which a thread of soil of size about 2-3mm begins to crumble when rolled. About 2g of the ripened soil was rolled on a porcelain plate using the hand to sizes of about 2-3mm without it breaking or sticking. When it developed cracks and could crumble, a little amount was taken and tested for water content.
4.5 Plasticity Index (PI) The plasticity index is the difference in moisture content between the liquid and plastic limits. As the soil particles exhibit a higher tenacity for water molecules, the liquid limit increases more rapidly than the plastic limit. As a result, the higher the PI, the more active a soil tends to be. Ndofor Akongnui Fai
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33 High PI soils are prone to significant shrinking and swelling with a subsequent loss of strength. A high Plasticity Index indicates that the material has significant clay content; it is more plastic and compressible and has greater volume change characteristics. The plasticity index has proven to be one of the most useful of all soil indices and is essential to the description of a cohesive soil. Table 4 shows a summary of the Atterberg limits and plasticity indices for the various samples. From these values, samples FET and FBM will plot in the zone corresponding to kaolinite while FNB and FNK will plot in that corresponding to finer and swelling clays on a plasticity chart. This tells us FET and FBM maybe richer in kaolinite than the others keeping other factors apart. The high plasticity indices for FBM, FNB and FNK tells us they should have a high affinity for water which may be due to the presence of swelling clays or colloidal materials in them. Table 4, Atterberg limits and Plasticity indices for the various samples
Sample
Liquid limit
Plastic limit
Plasticity index
FET
56.7
37.3
19.4
FBM
64.1
36.2
27.9
FNB
56.6
29.1
27.5
FNK
62.9
23.8
39.1
4.6 Loss on Ignition By heating the soil samples to very high temperatures, and measuring the weight loss (loss on ignition) after burning at selected temperatures, we were able to determine which clay minerals maybe present in the samples and their relative amounts. Normally, kaolinite is dehydroxylated between 450°C and 550°C and losses about 13.95% its original weight. To carry out this experiment, we need a mass balance, drying oven, and crucibles. The following procedure is followed. 1. The crucible is weighed using the mass balance 2. The sample is placed in the crucible and their combined weight measured. 3. The sample is then dried in the oven at 105°C until dry (may take up to a day). Ndofor Akongnui Fai
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34 4. The crucible + dried sample are weighed. The difference yields the water content 5. The oven is set at various temperatures ranging from 105 to 600°C and the crucible left in it for at least 1 hour at each temperature. 6. The crucible is removed from the oven and allowed to cool briefly. 7. Crucible + sample are re-weighed. The difference from the dry state yields the loss on ignition. Based on the results obtained from all the samples, we were able to estimate the amount of kaolinite in each sample. From figure 16, the rate of weight loss on ignition between 450 - 550°C is very reasonable. This can be attributed to the dehydration of kaolinite. This tells us there is a reasonable amount of kaolinite in the FET sample. Observing figure 17, we have about a 6% loss in weight between 450 - 550°C which indicates that about 40% of the soil is made up of kaolinite. However, we observe that below 450°C, we have a loss of about 4%, which can be attributed to other clay minerals which should be swelling clays and colloidal materials. temperature (o C) 105
150
200
250
300
350
400
450
500
550
600
rate of weight loss
0 2 4 6 8 10 12 14
Figure 16, Incremental loss on ignition at various temperatures - FET
Total weight loss (%)
12 10 8 6 4 2 0 105
150
200
250
300
350
400
450
500
550
600
o
temperature ( C)
Figure 17, Total loss in weight at various temperatures - FET
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35 From figure 18, the rate of weight loss between 450 - 550°C can be attributed to the loss of water from kaolinite. This tells us there is a reasonable amount of kaolinite in the FBM sample. Observing figure 19, we have about a 6.2% loss in weight from 450 - 550°C telling us about 4045% of the soil is made up of kaolinite. This sample seems to be that with the least amount of swelling clays and/or colloidal material, since we observe from figure 19 that below 450°C, we have a loss on ignition slightly below 2%.
temperature (o C) 105
150
200
250
300
350
400
450
500
550
600
0
rate of weight loss
2 4 6 8 10 12 14
Figure 18, Incremental loss on ignition at various temperatures – FBM
Total loss in weight (%)
10 8 6 4 2 0 105
150
200
250
300
350
400
450
500
550
600
tempeature (o C)
Figure 19, Total loss in weight at various temperatures – FBM
From figure 20, the rate of weight loss on ignition between 450°C and 550°C is quite much and also very outstanding. This loss corresponds to the dehydration of kaolnite, which tells us there is a reasonable amount of kaolinite in the FNK sample. Observing figure 21, we have about a 6% loss in weight from 450 - 550°C telling us about 40% of the soil is made up of kaolinite.
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36 However, from figure 21, this sample also may be contents a reasonable amount of swelling clays and/or colloidal materials given the ±4% loss below 450°C.
temperature (o C) 105
150
200
250
300
350
400
450
500
550
600
0
rate of weight loss
2 4 6 8 10 12 14
Figure 20, Incremental loss on ignition at various temperatures – FNK
Total weight loss (%)
12 10 8 6 4 2 0 105
150
200
250
300
350
400
450
500
550
600
o
temperature ( C)
Figure 21, Total loss in weight at various temperatures – FNK
From figure 22, we have a high rate of loss in weight upon ignition occurring between 450 550°C. This corresponds to loss of water from kaolnite, which tells us there is a reasonable amount of kaolinite in the FNB sample. Observing figure 23, we have about a 6% loss in weight from 450 - 550°C telling us about 40% of the soil is made up of kaolinite. This sample is also made up of a reasonable amount of maybe swelling clays and/or colloidal material given the ±5% loss below 450°C shown in figure 23.
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37
temperature (o C) 105
150
200
250
300
350
400
450
500
550
600
rate of weight loss
0 2 4 6 8 10 12 14
Total loss in weight (%)
Figure 22, Incremental loss on ignition at various temperatures – FNB
14 12 10 8 6 4 2 0 105
150
200
250
300
350
400
450
500
550
600
o
temperature ( C)
Figure 23, Total loss in weight at various temperatures - FNB
From the loss on ignition results presented above, we can say all these samples most likely contain the amount of kaolinite which a soil should have in order to satisfy one of the most important selection criteria for the MIP technique [29]. However, we cannot be very certain and sure bearing in mind that dehydroxylation of other minerals especially amorphous silicates or organic matter between 450 - 550°C can mislead us. Sample FBM stands out as the best based on the fact that below 450°C, we observe only a ±2% loss on ignition while for the other 3, it is doubled or more. The other samples could therefore content reasonable amounts of undesired components.
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38
Chapter-5
Methodology
5.1 Materials The specimens for this study were fabricated using the following four components; kaolinitic soils from Cameroon (FBM, FET, FNB and FNK), 30% sodium hydroxide solution, distilled water and fine-grained sand. The soil samples were sun dried and sieved with only grain sizes below 425 m used for specimen fabrication, except for 2 series of specimens whose grain sizes were below 212 m and 106 m. The 30% Sodium hydroxide solution, fine-grained sand and distilled water were supplied by the laboratory.
5.2 Fabrication of Specimens From equation (6), for a complete reaction between kaolinite and sodium hydroxide to take place, we need 2 moles of sodium hydroxide to react with 1 mole of Kaolinite. We started with an initial sodium hydroxide content of 8% weight of soil because we never have full conversion and at 8%, we are not far from equilibrium, taking into consideration the kaolinite content of the soils indicated from their loss on ignition. Water contents slightly below plastic limits were used for the first series of samples. This was to take care we do not use excessively high water contents , for this will result in non-homogenous mixtures and when the water evaporates empty cavities are left in the materials and this has negative effects on their strength and stability. Keeping the compositions of the other components constant, the water contents were first of all varied so that we could get the optimum water content for each sample. After obtaining the optimum water content, optimum contents for the other components were determined by keeping the amounts of the three other components constant while using variable amounts of the fourth component in each series. To optimize the amount of sodium hydroxide, for each series, we also considered the fact that very low or very high amounts of sodium hydroxide will not give us good results. Very small amounts will not lead to the reaction of all the kaolinite present and so will lead to weak network polymers to bind the soil and sand grains together. Very high amounts of sodium hydroxide on the other hand may result in the material having un-reacted sodium hydroxide, which leads to
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39 increase efflorescence (reaction between sodium hydroxide and carbondioxide to produce sodium carbonate precipitates), low stability and little durability. High amounts of sodium hydroxide will also unnecessarily increase cost. 5.2.1
Mixing
The mixer we used was the Small Hobart mixer. Components were all weighed separately and put into the mixer systematically. The sodium hydroxide solution was first weighed in a small plastic container. The required distilled water was then added to it and the mixture well shaked and closed. In some cases, water had to be subtracted from the sodium hydroxide solution. The required amount of solution was weighed and put in an oven at 105°C until the amount of excess water evaporates. The sand and soil were first put into the bowl of the mixer and mixed at speed 1 (~107 revolutions/minute) for about one minute. The sodium hydroxide solution/distilled water mixture was then added into the mixer while it was rotating at speed 1. Mixing continued in speed 1 for 2 minutes after which the mixer was stopped and the speed changed to speed 2 (~198 revolutions/minutes), in which the mixing lasted 10 minutes. In most cases, mixing was interrupted in order to remove samples stuck in the rotating arm or the walls and bottom of the bowl using a spoon. The mixture was also well inspected to see if it was dry or not (determine if the rheology is good). 5.2.2
Moulding
Moulding was carried out using a cylindrical steel mould. With the internal pressure of the oil at pressures of 60bar, compaction pressures of about 150bar (15MPa) were applied. After mixing, 10 specimens of approximately 50g each were moulded. This was done as fast as possible in order to avoid drying which will result in a decrease in workability. Specimens had various heights with an average about 45mm and diameters averagely 25mm. After moulding, the specimens are numbered, weighed and immediately put in an oven set at 80°C for curing. In order to check if there was swelling, the dimensions of one series of specimens were measured immediately after moulding. Comparing these dimensions with those after post curing we could determine if there was swelling or not.
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40 5.2.3
Curing
Specimens were cured for about 24hours in an oven set at a constant temperature of 80°C. After curing, the specimens were removed from the oven and allowed to cool. They were again weighed and properly numbered and labeled. The samples were now ready for post curing, which was carried out under different conditions similar to those in which building materials are exposed to naturally. 5.2.4
Post curing and Pre-test Treatments
For each series of specimens, the first 3 (specimens 1, 2 and 3) were put in an oven set at a constant temperature of 40°C for at least 7 days. The next 3 (specimens 4, 5 and 6) were immersed in water for at least 7 days. The third group of 3 specimens (specimens 7, 8 and 9) underwent at least five cycles of drying and wetting, i.e. at least 5 days in the oven set at 40°C and at least 5 days immersed in water. This third group of specimens had to be immersed in water for at least 24 hours before the strength test. The last specimen (specimen 10), was half immersed in distilled water in order to check efflorescence. When partially immersed, water transports un-reacted chemicals and soluble substances from the immersed zones of specimens to the upper un-immersed surfaces. The deposited material was either whitish or reddish in color and in some cases grows into needle-like structures. This deposition of un-reacted chemicals and soluble substances on specimen surfaces is what is referred to as efflorescence. This is an indication of possible degradation as the un-reacted sodium hydroxide causes degradation of the material’s structure with time.
5.3 Measurements Some measurements were carried out on the specimens after moulding, curing and post curing before testing for strength. The measurements were as follows. 1. Mass after moulding W1 (g) 2. Mass after curing W2 (g) 3. Mass after post curing W3 (g) 4. Diameter (mm) 5. Height (mm)
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41 From the dimensions measured, the areas and volumes of specimens were calculated and using the masses measured, we calculated the density of specimens. Density d = W/V ……………………………………………………… (7) Volume v = (H x (D/2)2 x ) ………………………………………….. (8) Where d = density of specimen (g/cm3) W= mass of specimen (g) V = volume of specimen (cm3) H = height of specimen (cm) D = diameter of specimen (cm) Densities of some specimens were measured after moulding (d1), after curing (d2) and after post curing for specimens kept in the oven at 40°C (d3). From this, we calculated the change in densities at different stages as follows: d1 = ((d1-d2)/d2) x 100% ……………………………………………….. (9) d2 = ((d3-d2)/d2) x 100% ……………………………………………….. (10) Where d1 = change of density percentage after curing d2 = change of density percentage after post curing
5.4 Testing The specimens were tested on compressive strength and stability in the presence of water. 5.4.1
Uniaxial Compression test
After measuring the weights and dimensions of the immersed and cycled specimens, they were immediately put back into water until they have to be tested for strength. Before testing the wet specimens for strength, they are removed from water and dried using a paper towel. The compression test was carried out using a uniaxial compression test apparatus. Steady loads were applied and increased at a rate of 1mm/minute until failure. The maximum scale for the load applied before failure is then read alongside with the percentage. From these values, the maximum load applied before failure is calculated. The uniaxial compressive strength is calculated from the relationship; S = F/A ……………… (11) Where S = uniaxial compressive strength (N/mm2) Ndofor Akongnui Fai
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42 F = maximum load applied before failure (N) A = cross sectional area of the specimen (mm2) The compressive strengths for the specimens kept constantly dry in the oven at 40°C is represented as S1, for the specimen immersed in water as S2, for the specimens cycled and kept in water at least 24 hours before testing (dry/wet) as S3. 5.4.2
Loss of compressive strength
Upon comparing the compressive strengths of specimens subjected under the 3 different conditions, we were able to appreciate their stabilities and quality under various conditions. Loss of compressive strength was calculated as shown in equations 12 and 13. L1 represents loss of compressive strength due to immersion, while L2 represent the loss of compressive strengths due to cycling. L1 = (1-(S2/S1)) x 100% …………………………………….. (12) L2 = (1-(S3/S1)) x100% …………………………………….... (13)
5.5 Water Absorption The immersed specimens usually absorb some water. The average percentage water absorption (A %) for each series of specimens was calculated as follows : A% = ((W3-W2)/W2) x 100%.................................................................. (14)
5.6 Efflorescence and pH We also made observations in order to determine if there was efflorescence for each series of specimens. As mentioned before, this was done on the specimens that were half immersed in water. The pH of the water in which the specimens were half immersed was also measured regularly. For some of the half immersed specimens, the measurement of pH was done about every four days after which the specimen and container are properly washed with distilled water and the water changed.
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43
5.7 Homogeneity of the mixture We had to make sure that the composition of all specimens of the same series was then same. In order to make sure this was the case, the homogeneity of all specimens of the same series was evaluated using the following relationship; (W1-W2)/W2 ……………………………………………………… (15) The value obtained for specimens of the same series had to be almost the same otherwise, the specimens were discarded and new specimens for that series made again.
5.8 Checking the effect of maximum grain size of soil samples Apart from 2 series of specimens, all series of specimens were fabricated using soil samples whose maximum grain size was 425 m. This was done by first crushing the soil, and then only the portion that could pass through a sieve with diameter 425 m used for specimen fabrication. In order to check if the maximum grain size has an influence on the properties of the resulting material, we decided to produce 2 series of specimens of the FBM sample with maximum grain sizes of 212 m and 106 m. The properties of these two series of specimens were then compared with those of the specimens with maximum grain size of 425 m.
5.9 Checking the effect of curing temperature The normal curing temperature we used was 80°C. In order to check if the curing temperature has any effects on the properties of the materials, we produced 10 specimens from the FBM sample and varied curing temperature. This was the FBM13 series. Specimens FBM13-1, FBM13-2 and FBM13-3 were cured at 60°C, specimens FBM13-4, FBM13-5 and FBM13-6 were cured at 105°C while specimens FBM13-7, FBM13-8 FBM13-9 and FBM13-10 were cured at 130°C. After curing, all the specimens were kept dried before testing. Their properties were then compared in order to evaluate the influence of curing temperature.
5.10 Improving specimen’s characteristics using sodium hydroxide We decided to make one series of specimens; FBM12 without sodium hydroxide. Comparing the characteristics of this series of specimens and those of other series with variable amount of sodium hydroxide, we could appreciate the stabilization effects of sodium hydroxide.
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F E T F E T 214311114445(g9880)....7086 22239990(g671)....4062 1111(22g....)08903443(816g....)94715555(g0000) (1111% 0000) (2222% 0000) (% 8888) (% 23226084) F E T F E T F E T 5 1 4 8 . 8 2 9 7 . 6 1 4 . 9 3 8 . 7 5 0 1 0 2 0 1 0 26 F E T 6 1 5 0 . 6 3 0 1 . 2 9 . 0 3 9 . 2 5 0 1 0 2 0 6 F E T F T 879112751613...157 232601433...107 11647...11143559...746555000 111000 1215000 848 22226666 FE E T 6F.o1r.1theF m iarsbtrifcoautriosenroiaefssS ,tpehepectiw aetenrstacnotn.tW enetw asvarieednvsiim ultaneousaltyerw p5o% rtifoonroFfE th1e ow thheicrhcw ofm choinlethettnht(e1o0pfro3% aesprosisnlieegnhtottslyaw bveelrokyw tihccekoypnlsm asitxictulriem tinaitinhtdiathlaeysam nadtecsraoiagnletedsntiatcksw ainm stahnedsotT T iw h s g a v s t ,iaw geeotw neetihgw eatm ixciongnt)eanram hile. a l s o f t h e m i x e r . T h i s w a s d i s c a r d e d n d w e d e c i d e d t o r e d u c h e r t a n d a dgooubd,leesthpeecsiaanldycFoE nT te9nw t.hT hhew w osrknaobtialibtyleotofsbeerim esixF E T 1e,lFE T 2t,fF E T 8daansdinFgE T 9lum w apsw nhoitcqhuglisotoet i c a e d w a s i o r m e l e sFtE ocT k3otontFhE em inogrkaarbm heasm eiftihrstth2em 7,ixw iliotyftw qiuxietreagfoterd,thw m ainteurteiaslolofm kiinxgingquaittesploedse2a.nF doreasseyrietos com pact.T
44
Chapter-6
Observations, Results and Discussions
6.1 Mvog Betsi sample, (FET) Nine series of specimens with different compositions were prepared. The first component we had to verify its required composition by weight with respect to that of the soil was water. After coming out with the optimum water content, the next component to optimize was sodium hydroxide and lastly the sand content. Table 5 shows the composition by weight and the percentage by weight of the various components for each series of specimens. Table 5, Composition of each series of specimens - FET Series No.
Clay
Composition by Weight of Filler (sand) NaOH
Ndofor Akongnui Fai
Water
Total Weight
Clay
Percentage by Weight of Filler NaOH water
PHYLARES 2006
45 We observed that at optimum water contents (26%), if we increase the sand content, this resulted in good workability. Exceeding the optimum water content resulted in the material sticking to the walls of the mixer and on the mixing arm. Since the sodium hydroxide solution and water were first mixed in a plastic container before adding to the soil/sand mixture, it was observed that the best means of adding was bit by bit while the mixer is mixing the soil/sand mixture at speed 1. This was implemented from FET3 to FET9. At the start of mixing, large shapeless granules were formed, which progressively break down into small coherent granules as all the material gets wet. All specimens of series FET1 to FET7 were quite good with no difficulties during moulding. Specimens of series FET8 were however difficult to be moulded, for they were wet and sticky, surely because of inadequate amount of sand. Series FET9 was not moulded at all for even mixing it was impossible. 6.1.2
Physical Characteristics of Specimens
6.1.2.1 Density The highest densities were obtained immediately after moulding (d1). These generally decreased from about 10.38% in FET3 to 12.75% in FET1 after the specimens are cured (d2). After post curing, the densities of the dry samples kept at 40°C also changed from those obtained after curing, though not as significant as from moulding to curing. For the FET1 series, there was no change after post curing. From series FET2 to FET4, there was a decrease in density in the range 0.25% to 6.11% and from series FET5 to FET8, there was an increase in the range 0.10% to 0.25% after post curing. Changing the proportion of the various components resulted in a change of density as we can observe on the results presented in tables 6 to 8. The variation of density with percentage sodium hydroxide for specimens having same water and sand content is shown in figure 24. The general trend shows an increase in density when amount sodium hydroxide is increased. Immediately after moulding we observe that density d1 at 4% sodium hydroxide (FET7) increases from 2.152g/cm3 to 2.20g/cm3 at 8% and 10% sodium hydroxide (FET4 and FET5 respectively), meaning that after 8% sodium hydroxide the density does not change considerably. The same
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46 trend of increase in density with increase in sodium hydroxide is also observed after curing and after post curing. Table 6, Variation of density with NaOH content - FET Series No. FET7 FET6 FET4 FET5
d1 2.152 2.171 2.203 2.202
Average density (g/cm3) d2 1.944 1.963 1.981 1.991
d3 1.947 1.968 1.986 1.993
Change in density (%) d1 d2 10.70 0.15 10.60 0.25 11.21 -6.11 10.60 0.10
Percentage by weight NaOH (%) 4.00 6.00 8.00 10.00
Table 7, Variation of density with water content - FET Series No. FET3 FET2 FET4 FET1
d1 2.191 2.202 2.203 2.202
Average density (g/cm3) d2 1.985 1.983 1.981 1.953
d3 1.979 1.978 1.986 1.953
Change in density (%) d1 d2 10.38 -0.30 11.04 -0.25 11.21 -6.11 12.75 0.00
Percentage by weight water (%) 24.00 26.00 28.00 30.00
Table 8, Variation of density with sand content - FET Series No. FET8 FET2
Average density (g/cm3) d1 d2 d3 1.955 1.731 1.933 2.202 1.983 1.978
Change in density (%) d1 d2 12.94 11.67 11.04 -0.25
Percentage by weight sand (%) 150.00 200.00
We observe from figure 25 that density varies when water content is varied. Density after moulding increases from 2.191g/cm3 at 24% water to 2.202g/cm3 at 30% water. After curing and post curing, we obtain optimum densities at 26 and 28% water content. Looking at compressive strength and water absorption results later, at 26% and 28% water, there is no great difference. The optimum water content should therefore be between 26 and 28%. We decided to work with 26% considering the fact that increase in water will result in many pore spaces after evaporation and thus a decrease in strength and stability. In order to check if the amount of sand in the material affects, its properties, we made 2 series of samples FET8 and FET9 with 150% and 100% sand contents respectively. It was impossible to
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PHYLARES 2006
47 mix FET9 as it was sticking on the walls of the mixer and the mixing arm after 2 minutes of mixing and was thus thrown away. The samples with 200% sand showed very good workability but FET8 had a poorer workability and moulding was a bit difficult. From figure 26, densities measured after moulding d1, after curing d2 and after post curing for the dried samples were higher for the series with 200% sand.
Variation of density with % NaOH - FET
density (g/cm3)
2,25 2,2
af ter moulding
2,15
af ter curig
2,1
dried specimens af ter post curing
2,05 2 1,95 1,9 1,85 1,8 4,00
6,00
8,00
10,00
% NaOH
Figure 24, Variation of density with % NaOH – FET
Variation of density with water content - FET 2,25
density (g/cm3)
2,2 2,15
af ter moulding
2,1 af ter curing
2,05
dried specimens af ter post curing
2 1,95 1,9 1,85 1,8 24,00
26,00
28,00
30,00
water content (%)
Figure 25, Variation of density with water content – FET
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48 Variation of density with sand content - FET 2,5
density (g/cm3)
2
1,5
150% sand 200% sand
1
0,5
0 d1
d2
d3
Figure 26, Variation of density with sand content - FET
6.1.2.2 Water Absorption The results in tables 9 to 11 show how immersed specimens absorbed water. We observed that water absorption depends on the composition of the specimen. Figure 27 shows the effects of changing the sodium hydroxide content on water absorption. The highest water absorption (11.62%) occurred at 4% sodium hydroxide and reduced with increase in sodium hydroxide until 8% sodium hydroxide where we observed minimum absorption (10.53%). After 8%, going to 10% sodium hydroxide content, we notice that the water absorption is constant. From figure 28, we observe that there is a decrease in water absorption with increase in water content till a water content of 28%. At 28% water content, we have the least water absorption, after which it starts increasing with an increase in water content. Though it is least at 28%, the difference is not really much (<1% decrease) compared to that at 26% water, so we decided to choose 26% as the optimum. Table 9, Variation of water absorption with NaOH content - FET Series No. FET7 FET6 FET2 FET5
Ndofor Akongnui Fai
Average weight (g) W2 W3 45.60 50.90 44.37 49.33 45.60 50.40 43.87 48.50
Water absorption (%) 11.62 11.18 10.53 10.55
NaOH % 4.00 6.00 8.00 10.00
PHYLARES 2006
49 Table 10, Variation of water absorption with water content - FET Series No. FET3 FET2 FET4 FET1
Average weight (g) W2 W3 44.83 49.53 45.60 50.40 44.50 49.17 43.73 48.82
Water absorption (%) 10.48 10.53 10.49 11.64
Water % 24.00 26.00 28.00 30.00
Variation of water absorption with NaOH content - FET 11,80
water absorption (%)
11,60 11,40 11,20 11,00 10,80 10,60 10,40 10,20 10,00 9,80 4,00
6,00
8,00
10,00
% NaOH
Figure 27, Variation of water absorption with NaOH content - FET
Variation of water absorption with water content - FET
water absorption (%)
14,50 14,00 13,50 13,00 12,50 12,00 11,50 11,00 24,00
26,00
28,00
30,00
water content (%)
Figure 28, Variation of water absorption with water content - FET
From table 11 and figure 29, the samples with 150% sand absorbed more water (11.43%) than those with 200% sand (10.53%).
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50 Table 11, Variation of water absorption with sand content - FET Series No. FET8 FET2
Average weight (g) W2 W3 45.5 50.7 45.6 50.4
Water absorption (%)
Sand %
11.43 10.53
150.00 200.00
Variation of water absoprtion with sand content - FET
water absorption (%)
11,60 11,40 11,20 11,00 10,80 10,60 10,40 10,20 10,00 150,00
200,00
sand %
Figure 29, Variation of water absorption with sand content – FET
6.1.3
Compressive strength and Stability
Changing the water content resulted in a change in compressive strength as indicated by the results shown in table 12. These results are presented in figure 30, from which we observe that at 24% and 26% water, the compressive strengths for the dry specimens is almost the same (about 7MPa) and almost the same trend observed for the immersed and cycled specimens, with strengths of about 3MPa. Above 26% water, the compressive strength starts falling from about 6MPa at 28% water to about 3MPa at 30% for the dried specimens. A similar trend is observed for the immersed and cycled specimens though with the strengths about half those of the dry specimens. The average loss in compressive strength of the immersed specimens is 50.8%, while for the cycled specimens its 52.4%. The values obtained show us that the optimum water content (26% water) is very important, for at lower or higher water contents we will have low strengths.
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51 Table 12, Variation of compressive strength with water content - FET Series No.
Water %
FET3 FET2 FET4 FET1
24.00 26.00 28.00 30.00
Compressive strength (MPa) S1 6.90 6.90 5.83 2.97
S2 3.10 3.07 2.97 1.67
S3 3.33 3.07 2.70 1.53
Loss of strength (%) L1 55.07 55.51 49.06 43.77
L2 51.74 55.51 53.69 48.48
compressive strength (MPa)
Variation of compressive strength with water content - FET 8 7 6 5
S1, dried specimens S2, immersed specimens S3, cycled specimens
4 3 2 1 0 24,00
26,00
28,00
30,00
water content (%)
Figure 30, Variation of compressive strength with water content – FET
The results of change of compressive strength due to changing sodium hydroxide compositions are presented in table 13 and figure 31. Generally, compressive strengths of the immersed and cycled specimens are almost the same and about half of those of the dried specimens for each series of specimens. We notice that increasing the sodium hydroxide content from 4% to 10% results in an increase in compressive strength. At 4% sodium hydroxide, the dried specimens have strengths of about 1.6MPa, while the immersed and dried specimens have strengths of about 0.5MPa. At 10% sodium hydroxide, these strengths are about 6MPa and 2.9MPa respectively. We also notice that there is no great difference between the strengths at 8% and 10% sodium hydroxide. This tells us that at 8% sodium hydroxide, the reaction between the kaolinite in the soil and sodium hydroxide is complete. The highest loss in strengths for both immersed and cycled specimens are obtained at 4% sodium hydroxide; 70.25% and 68.99% respectively. We now can actually appreciate the fact that sodium hydroxide has an influence in the compressive strengths and will give very good results when the right amounts are used at optimum water and sand content.
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52 Table 13, Variation of compressive strength with NaOH content - FET Series No.
NaOH %
FET7 FET6 FET2 FET5
4.00 6.00 8.00 10.00
Compressive strength (MPa) S1 1.58 2.23 6.90 6.17
S2 0.47 0.92 3.07 2.83
Loss of strength (%)
S3 0.49 0.97 3.07 2.90
L1 70.25 58.74 55.51 54.13
L2 68.99 56.50 55.51 53.00
compressive strength (MPa)
Variation of compressive strength with % NaOH - FET
8 7 6 5
S1, dried specimens S2, immersed specimens S3, cycled specimens
4 3 2 1 0 4,00
6,00
8,00
10,00
% NaOH
Figure 31, Variation of compressive strength and NaOH content – FET
Looking at table 14 and figure 32, samples with 200% sand have higher compressive strengths than those with 150% sand. The loss in strength due to immersion and cycling is higher in the samples with 150% sand. Normally if we had succeeded in mixing and moulding the samples with 100% sand, their compressive strengths would also have been lower than those of the 200% sand. Table 14, Variation of compressive strength with sand content - FET Series No.
sand %
FET8 FET2
150.00 200.00
Ndofor Akongnui Fai
Compressive strength (MPa) S1 1.47 6.90
S2 0.67 3.07
S3 0.57 3.07
Loss of strength (%) L1 54.42 55.51
L2 61.22 55.51
PHYLARES 2006
53 Variation of compressive strength with sand content - FET
compresive strength (MPa)
8 7 6 5 150% sand
4
200% sand
3 2 1 0 S1
S2
S3
Figure 32, Variation of compressive strength with sand content – FET
6.1.4
Efflorescence
The pH of the water in which specimen ten for each series was immersed was measured after 1 day for each series and it was noticed that it varied form 10 to 11. pH values decreased with time until at about 1 month when we had values of about 7 to 7.2. The colour of the water never changed, which indicated that the material leached was colourless. All the specimens were also quite stable in water. After 3 days in water, the upper part of the specimens which was not covered by water was usually covered by little soft and white needle-like substances. This indicates efflorescence (deposition of sodium carbonate resulting from the reaction between sodium hydroxide and carbondioxide). For those that were kept for about two months, we noticed some sort of degradation or erosion on the upper surfaces.
6.2 Bambili sample, (FBM) Thirteen series of specimens were prepared from the Bambili soil. As stated before, the first component we verified its required composition by weight with respect to that of the soil was water. After coming out with the optimum water content, the next component to optimize was sodium hydroxide and lastly the sand content. The composition by weight and the percentage by weight of the various components for each series of specimens are shown in table 15.
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54 Table 15, Composition of each series of specimens - FBM Series No. FBM1 FBM2 FBM3 FBM4 FBM5 FBM6 FBM7 FBM8 FBM9 FBM10 FBM11 FBM12 FBM13
6.2.1
Clay (g) 148.0 150.0 150.6 148.8 147.9 149.7 150.6 174.9 211.9 89.30 89.30 152.4 150.6
Composition by Weight for Filler (sand) NaOH Water (g) (g) (g) 296.0 11.8 44.4 299.4 12.0 38.9 301.2 12.0 36.1 297.6 11.9 41.7 295.9 14.8 41.4 299.4 9.0 41.9 301.2 6.0 42.2 262.2 14.0 48.9 211.9 16.9 59.3 178.6 7.1 25.0 178.6 7.0 25.0 304.9 0 42.9 301.2 12.0 36.1
Total Weight (g) 500 500 500 500 500 500 500 500 500 300 300 500 500
Percentage by Weight of Clay Filler NaOH (%) (%) (%) 100 200 8 100 200 8 100 200 8 100 200 8 100 200 10 100 200 6 100 200 4 100 150 8 100 100 8 100 200 8 100 200 8 100 200 0 100 200 8
water (%) 30 26 24 28 28 28 28 28 28 28 28 28 28
Fabrication of specimens
With a water content of 30%, the first series FBM1 had a lot of water in it during mixing, reason why it was difficult to be moulded as compaction was difficult. Stepping down to a water content of 26% for FBM2, workability was good and compaction good also. For FBM3 with a water content of 24%, the mixture was dry and compaction not quite good, though workability was ok. Series FBM4, FBM5, FBM6, FBM7, FBM10, FBM11, FBM12 and FBM13, showed good workability and compaction. FBM8 was quite moist and resulted in poor compaction as the specimens had some fissures and indentations. Generally, good workability and compaction were achieved at water contents of 28% and sand contents double the soil content. Sand contents below this were not favorable. Specimens of all the series were quite stable. 6.2.2
Physical Characteristics of Specimens
6.2.2.1 Density Tables 16 to 18 show results of the variation of density with sodium hydroxide, water and sand content respectively. The various changes in density as a result of keeping the specimens constantly immersed in water or cycling them are also shown on these tables. The highest densities were obtained immediately after moulding (d1). These generally decreased from about
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55 10.02% in FBM3 to 12.94% in FBM1 after the specimens are cured (d2). After post curing there was a slight increase or decrease in density, but mostly increased in the range 0.1% to o.86%. From figure 33, we observe that an increase in sodium hydroxide content results to very slight changes in density under the three conditions. For the dried specimens, at 4% sodium hydroxide the density is 2.135g/cm3 and reduces to 2.087g/cm3 at 10% sodium hydroxide, which is insignificant. Table 16, Variation in density with NaOH content - FBM Series No. d1 2.135 2.135 2.112 2.087
FBM7 FBM6 FBM4 FBM5
Average density (g/cm3) d2 1.914 1.923 1.903 1.864
d3 1.912 1.926 1.913 1.880
Change in density (%) d1 d2 11.55 -0.10 11.02 0.16 10.98 0.53 11.96 0.86
Percentage by weight NaOH (%) 4.00 6.00 8.00 10.00
Variation of density with % NaOH - FBM 2,2
density (g/cm3)
2,15 2,1 2,05 2
after moulding
1,95
after curing
1,9
dried after post curing
1,85 1,8 1,75 1,7 4,00
6,00
8,00
10,00
% NaOH
Figure 33, Variation of density with NaOH content – FBM
From a water content of 24%, we observe an increase in density with increasing water content until a water content of 28% whereby the density reduces slightly for the immersed and the cycled specimens as shown in figure 34. A decrease in density ranging between 10.02% for FBM3 to 12.94% for FBM1 with an increase in water content is also noticed after curing. A slight increase in density is noticed after post curing for FBM3, FBM2 and FBM4, while we have a slight decrease of 0.32% for FBM1. At 28% water, we have the optimum densities for the immersed and cycled specimens, so we fixed 28% as the optimum water content.
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56 Table 17, Variation of density with water content - FBM Series No. d1 2.031 2.070 2.112 2.130
FBM3 FBM2 FBM4 FBM1
Average density (g/cm3) d2 1.846 1.872 1.903 1.886
d3 1.85 1.875 1.913 1.880
Change in density (%) d1 d2 10.02 0.22 10.58 0.16 10.98 0.53 12.94 -0.32
Percentage by weight water (%) 24.00 26.00 28.00 30.00
Variation of density with water content - FBM 2,2 2,15
density (g/cm3)
2,1 2,05
af ter moulding
2
af ter curing
1,95 1,9
dried specimens after post curing
1,85 1,8 1,75 1,7 24,00
26,00
28,00
30,00
water content (%)
Figure 34, Variation of density with water content- FBM
Table 18 and figure 35 show how density varies with sand content. The density after moulding for the dried specimens generally decrease slightly with an increase in sand content from 2,137g/cm3 at 100% sand to 2.112g/cm3 at 200% sand. Similar trends are observed after curing and post curing. The general trend shows very insignificant changes in density when sand content is varied. Table 18, Variation of density with sand content - FBM Series No. FBM9 FBM8 FBM4
Ndofor Akongnui Fai
Average density (g/cm3) d1 d2 d3 2.137 1.864 1.922 2.132 1.860 1.916 2.112 1.858 1.913
Change in density (%) d1 d2 14.65 3.11 14.62 3.01 13.67 2.96
Percentage by weight sand (%) 100.00 150.00 200.00
PHYLARES 2006
57
Variation of de nsity with sand % - FBM 2,2
density (g/cm3)
2,15 2,1 2,05 af ter moulding
2 1,95
af ter curing
1,9
dried specimens af ter post curing
1,85 1,8 1,75 1,7 100,00
150,00
200,00
sand %
Figure 35, Variation of density with sand content – FBM
6.2.2.2 Water absorption Results of the changes in water absorption for the immersed specimens are presented in tables 19 to 21. Figure 36 shows the variation of water absorption with sodium hydroxide content. We observe that from 4% sodium hydroxide, water absorption increases from 11.95% to 13.40% at 6% sodium hydroxide. It then falls to 12% at 8% sodium hydroxide and after that it rises again to 13.01% at 10% sodium hydroxide. This is an indication that at 8% sodium hydroxide, we attain the optimum density, with very few pore spaces left to hold water.
Table 19, Variation of water absorption with NaOH content - FBM Series No. FBM7 FBM6 FBM4 FBM5
Ndofor Akongnui Fai
Average weight (g) W2 W3 45.17 50.57 44.77 50.77 45.60 51.07 44.80 50.63
Water absorption (%)
NaOH %
11.95 13.40 12.00 13.01
4.00 6.00 8.00 10.00
PHYLARES 2006
58 Variation of water absorption with NaOH content - FBM
water absorption (%)
14,0 13,5 13,0 12,5 12,0 11,5 11,0 4
6
8
10
% NaOH
Figure 36, Variation of water absorption with NaOH content – FBM
From figure 37 we observe that water absorption at a water content of 24% is 13.86%. It starts falling with an increase in water to a minimum of 12% at 28% water content, from which it starts rising again to 13.49% at 30% water content. This confirms the fact that 28% water content is the optimum for this sample, since at optimum, we have high densities and so least pore spaces to hold and/or transmit water. Table 20, Variation of water absorption with water content - FBM Series No. FBM3 FBM2 FBM4 FBM1
Average weight (g) W2 W3 43.5 49.53 44.17 49.8 45.6 51.07 43.67 49.56
Water absorption (%)
Water %
13.86 12.75 12.00 13.49
24.00 26.00 28.00 30.00
Variation of water absorption with water content - FBM
water absorption (%)
14,5 14,0 13,5 13,0 12,5 12,0 11,5 11,0 24
26
28
30
water content (%)
Figure 37, Variation of water absorption with water content - FBM
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59 Figure 38 presents the relationship between sand content and water absorption. At 100% sand content, the immersed specimens have water absorption of 14.78%. This increases to 16.07% at 150% sand and falls to 12% at 200% sand which means we have the best packing and densities at 200% sand. Table 21, Variation of water absorption with sand content - FBM Series No. FBM9 FBM8 FBM4
Average weight (g) W2 W3 42.43 48.7 42.93 49.83 45.60 51.07
Water absorption (%)
Sand %
14.78 16.07 12.00
100.00 150.00 200.00
Variation of water absorption with sand content - FBM
water absorption (%)
18,00 16,00 14,00 12,00 10,00 8,00 6,00 4,00 2,00 0,00 100,00
150,00
200,00
sand %
Figure 38, Variation of water absorption with sand content - FBM
6.2.3
Compressive strength and stability
Results of the change in compressive strength as a result of the change in the amount of various components are presented in tables 22 to 24. In table 22 we observe that at 0% sodium hydroxide, we have a compressive strength of 0.5MPa for the dried specimens. At 0% sodium hydroxide, the specimens were not stable in water so it was not possible to obtain strengths for immersed and cycled specimens. Looking at figure 39, from a sodium hydroxide content of 4%, compressive strength increases from about 5MPa to 12MPa at 10% sodium hydroxide for the dried specimens. There is also a corresponding increase in compressive strength for the immersed and cycled specimens with an increase in sodium hydroxide content, with values almost equal in both cases and about half those for the dried specimens for each series of
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60 specimens. Loss of compressive strength decreases with an increase in sodium hydroxide content. At 4% sodium hydroxide we have a loss of strength of 57.12% due to immersion and 59.62% due to cycling, which falls to 41.62% and 45.49% at 10% sodium hydroxide for immersed and cycled specimens respectively.
Table 22, Variation of Compressive strength with NaOH content - FBM Series No.
NaOH %
FBM12 FBM7 FBM6 FBM4 FBM5
0 4.00 6.00 8.00 10.00
Compressive strength (Mpa) S1 0.5 5.2 8.67 10.93 11.87
S2 2.23 4.1 6.37 6.93
S3 2.1 3.8 6.53 6.47
Loss of strength (%) L1 57.12 52.71 41.72 41.62
L2 59.62 56.17 40.26 45.49
Variation of Compressive strength with % NaOH - FBM
compressive strength (MPa)
14 12 10 S1, dried specimens
8
S2, immersed specimens S3, cycled specimens
6 4 2 0 4,00
6,00
8,00
10,00
% NaOH
Figure 39, Variation of compressive strength with NaOH content - FBM
Figure 40 shows variation of compressive strength with water content. At a water content of 24%, we have dry and wet compressive strengths of about 7MPa, and 6MPa respectively. These increase till we have maximum values of about 11MPa, and 7MPa for dried and cycled specimens respectively at 28% water content. After 28% water content, the compressive strengths start decreasing. The highest loss in strength is observed at 26% water content and the least at 24% water content for both immersed and cycled specimens.
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61 Table 23, Variation of compressive strength with water content - FBM Series No.
water %
FBM3 FBM2 FBM4 FBM1
24.00 26.00 28.00 30.00
Compressive strength (MPa) S1 7.43 10.20 10.93 4.80
S2 5.93 5.50 6.37 2.97
S3 6.57 5.10 6.53 3.73
Loss of strength (%) L1 20.19 46.08 41.72 38.13
L2 11.57 50.00 40.26 22.29
compressive strength (MPa)
Variation of compressive strength with water content - FBM 12 10 8
S1, dried specimens S2, immersed specimens S3, cycled specimens
6 4 2 0 24
26
28
30
water content (%)
Figure 40, Variation of compressive strength with water content - FBM
From figure 41, the compressive strengths under all conditions are lowest at 150% sand content. At 100% sand content the strengths are double those at 150% sand content. At 200% sand content we have the best compressive strengths under all conditions; their values are more than double those at 100% sand which tells us 200% sand should be the best sand content.
Table 24, Variation of compressive strength with sand content - FBM Series No. FBM9 FBM8 FBM4
Ndofor Akongnui Fai
sand % 100.00 150.00 200.00
Compressive strength (Mpa) S1 5.13 2.67 10.93
S2 2.32 1.17 6.37
S3 2.5 1.13 6.53
Loss of strength (%) L1 54.78 56.18 41.72
L2 51.27 57.68 40.26
PHYLARES 2006
62
compressive strength (MPa)
Variation of compressive strength with sand content - FBM 12 10 8
S1 dried specimens
6
S2 immersed specimens S3 cycled specimens
4 2 0 100
150
200
sand %
Figure 41, Variation of compressive strength with sand content – FBM
The compressive strengths for FBM5 were 11.87MPa, 6.93MPa and 6.47MPa under dried, immersed and cycled conditions respectively. Comparing them with those given by FBM4 which are 10.93MPa, 6.37MPa and 6.53MPa under dried, immersed and cycled conditions respectively, there is no significant difference. Also looking at the loss in strength values due to cycling and immersion for both FBM4 and FBM5, there is no great difference. Their densities too show no great difference. Looking at the water absorption of FBM4 due to immersion it is 12% and that of FBM5 is 13.1%. Taking all these properties into consideration and looking at the cost of production, a sodium hydroxide content of 8% will be the best for this sample. At 8% sodium hydroxide, almost all the kaolinite in the soil has been attacked and new minerals produced. Increasing sodium hydroxide will result in a material containing un-reacted sodium hydroxide which becomes harmful for the material as we noticed that the effervescence and degradation of FBM5 was the highest amongst all the series of specimens. Except series FBM8 and FBM9, that had a sand/soil ratio of 3/2:1 and 1:1, the other series of samples had a sand/soil ratio of 2:1. Comparing these 2 series to FBM4, we see that the best compressive strengths and least water absorption were obtained from FBM4, meaning the composition of FBM4 was the best. 6.2.4
Efflorescence
For all series of FBM, the pH of the water in which specimen 10 was half immersed was about 11 after 3-4hours. After 2 weeks, it fell to about 9 for all of them and after 30 days it was about 7 for series 4 and 5. All specimens except FBM12 were all stable in water. The colour of the water in which they were immersed never changed, indicating that the substances leached were Ndofor Akongnui Fai
PHYLARES 2006
63 colourless. White needle-like fibers (sodium carbonate due to reaction between sodium hydroxide and carbondioxide) grew at the upper surfaces of the specimens half immersed in water indicating efflorescence. This was the sample that showed the highest amount of efflorescence amongst all the four samples. 6.2.5
NaOH as stabilizing argent
To actually appreciate the stabilizing potentials of sodium hydroxide, we made a series of samples (FBM12) without adding sodium hydroxide into it. At optimum water and sand contents, workability and moulding was quite good. After curing for 24 hours, the specimens of series FBM12 had a different colour from those that had sodium hydroxide. It was lighter in colour, almost cream-like while the others were pink-like. We noticed that when the specimens were touched with fingers, a whitish powder is left on the fingers, but this was not the case with samples containing sodium hydroxide. After curing, we had to immerse some samples in water as we did for other series. Unfortunately, this series of specimens were not stable in water. When put in water, they totally crumbled after about ten minutes and became liquid. We therefore had no immersed and cycled specimens to test for compressive strength and water absorption. Densities followed the same trend like for the other series however. The highest density was after moulding, dropped after curing and increased after post curing. The compressive strength of the dried specimens was averagely 0.5MPa after keeping it for 10days in an oven set at 40°C. Table 25 and figure 42 show the relationship between sodium hydroxide content and compressive strength. From these results, we can really appreciate the stabilizing potentials of sodium hydroxide. At 8% sodium hydroxide, an increase in compressive strength of about 95% compared to when we have no sodium hydroxide at all. Table 25, Effects of NaOH on compressive strength - FBM
Ndofor Akongnui Fai
Series No.
water %
Sand %
NaOH %
Compressive strength S1 (MPa)
FBM12 FBM7 FBM6 FBM4 FBM5
28 28 28 28 28
200 200 200 200 100
0 4 6 8 10
0.50 5.20 8.67 10.93 11.87
PHYLARES 2006
64
Compressive strength (MPa)
Stabilization potentials of NaOH - FBM 14 12 10 8 6 4 2 0 0,00
4,00
6,00
8,00
10,00
% NaOH
Figure 42, Stabilization potentials of NaOH - FBM
6.3 Simbock sample, (FNB) For this sample, nine series of specimens with different compositions were also prepared. Table 26 shows the composition by weight and the percentage by weight of the various components for each series of specimens. Table 26, Composition of each series of specimens - FNB Series No. FNB1 FNB2 FNB3 FNB4 FNB5 FNB6 FNB7 FNB8 FNB9
6.3.1
Clay (g) 150.0 151.5 152.4 150.6 150.6 152.4 153.4 178. 217.4
Composition by Weight for Filler (sand) NaOH Water (g) (g) (g) 300.0 12.0 39.0 303.0 12.1 33.3 304.9 12.2 30.5 301.2 12.0 36.1 301.2 15.1 33.1 304.9 9.2 33.5 306.7 6.1 33.7 267.9 14.3 39.3 217.4 17.4 47.8
Total Weight (g) 500 500 500 500 500 500 500 500 500
Clay (%) 100 100 100 100 100 100 100 100 100
Percentage by Weight of Filler NaOH (%) (%) 200 8 200 8 200 8 200 8 200 10 200 6 200 4 150 8 100 8
water (%) 26 22 20 24 22 22 22 22 22
Fabrication of Specimens
The first series FNB1 had a water content of 26% and a sand content double (200%) that of the soil. The workability was good though it looked as if it had more water than required. Apart from FNB3 which was dry during mixing and FNB9 which was too wet and could not even be mixed,
Ndofor Akongnui Fai
PHYLARES 2006
65 the other series had good workability and compaction. For FNB9, the material was sticking on the mixing arm and the walls of the mixer when we started mixing at speed 2. This sample could not even be moulded and was thrown away. At optimum water contents (22%), if we increase the sand content, this resulted in good workability, while reducing sand content resulted in poor workability. Exceeding the optimum water content resulted in the material sticking to the walls of the mixer and on the mixing arm. The sodium hydroxide solution and water were first mixed in a plastic container before adding to the soil/sand mixture. It was observed that the best means of adding the water/sodium solution was bit by bit while the mixer was mixing the soil/sand mixture at speed 1. This was implemented from FNB3 to FNB9. At the start of mixing, large shapeless granules were formed, which progressively break down into small coherent granules as all the material gets wet. 6.3.2
Physical Characteristics of Specimens
6.3.2.1 Density The highest densities were observed after moulding (d1). These generally decreased from about 7.57% in FNB3 to 12.01% in FNB1 after the specimens were cured (d2). After post curing, the densities of the dry samples kept at 40°C also changed slightly from those obtained after curing, ranging from 0% in FNB6 to 0.25% in FNB2. From the results presented in tables 27 to 29, changing the proportion of various components resulted in a change of density. The variation of density with percentage sodium hydroxide for specimens having same water and sand content is shown in figure 43. The general trend shows an increase in density when amount sodium hydroxide is increased. Immediately after moulding we observe that density d1 at 4% sodium hydroxide (FNB7) increases from 2.019g/cm3 to 2.166g/cm3 at 8% sodium hydroxide. After 8% sodium hydroxide the density does not change considerably. The same trend is observed after curing and post curing. Optimum sodium hydroxide contents should thus be about 8%.
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66 Table 27, Variation of density with NaOH content - FNB Series No. FNB7 FNB6 FNB2 FNB5
D1 2.019 2.156 2.166 2.164
Average density (g/cm3) d2 1.877 1.957 1.965 1.952
Change in density (%) d1 d2 7.57 0.21 10.17 0.00 10.23 0.25 10.86 0.20
d3 1.881 1.957 1.970 1.956
Percentage by weight NaOH (%) 4.00 6.00 8.00 10.00
Variation of density with % NaOH - FNB 2,2 2,15
density (g/cm3)
2,1 2,05 af ter moulding
2 1,95
af ter curing
1,9
dried specimens af ter post curing
1,85 1,8 1,75 1,7 4
6
8
10
% NaOH
Figure 43, Variation of density with NaOH content – FNB
From figure 44, density varies when water content is varied. Density after moulding increases gently from 2.146g/cm3 at 20% water to 2.171g/cm3 at 24% water, and then falls slightly to 2.154g/cm3 at 26% water. After curing and post curing, we obtain optimum densities between 22% and 24% water content. The densities after curing and after post curing are almost the same for each series and are less than those after moulding. Looking at the results, the difference in densities at 22% and 24% water are not significant. Considering the lower changes in densities observed at 22%, we decided to take it as the optimum.
Table 28, Variation of density with water content - FNB Series No. FNB3 FNB2 FNB4 FNB1
Ndofor Akongnui Fai
D1 2.146 2.166 2.171 2.154
Average density (g/cm3) d2 1.959 1.965 1.962 1.923
d3 1.948 1.970 1.968 1.937
Change in density (%) d1 d2 9.55 -0.56 10.23 0.25 10.65 0.31 12.01 0.73
Percentage by weight water (%) 20.00 22.00 24.00 26.00
PHYLARES 2006
67 Variation of density with water content - FNB 2,2
density (g/cm3)
2,15 2,1 2,05
af ter moulding
2
af ter curing
1,95
dried specimens af ter post curing
1,9 1,85 1,8 1,75 20
22
24
26
water content (%)
Figure 44, Variation of density with water content - FNB
To check the effects of sand content on the properties of this soil sample, we prepared 2 series of samples; FNB8 with 150% sand and FNB9 with 100%. In addition to these 2 series, we had to use one of the series with 200% sand, however series FNB9 was thrown away because it was unable to be mixed and moulded. Table 29 and figure 45 show the relationship between density and change in density with sand content for 2 series of specimens. The best densities after moulding and after post curing for dried specimens are obtained at 150% sand content. After curing, the best densities are obtained for the specimens containing 200% sand. Changes in density after curing are more (12.58%) for the samples with 150% sand as well as after post curing (1.07%). Table 29, Variation of density with sand content - FNB Series No. FNB8 FNB2
Ndofor Akongnui Fai
Average density (g/cm3) D1 d2 d3 2.202 1.956 1.977 2.166 1.965 1.970
Change in density (%) d1 d2 12.58 1.07 10.23 0.25
Percentage by weight sand (%) 150.00 200.00
PHYLARES 2006
68 Variation of density with sand content - FNB 2,25 2,2
density (g/cm3)
2,15 2,1 2,05
150 % sand
2
200 % sand
1,95 1,9 1,85 1,8
d1
d2
d3
Figure 45, Variation of density with sand content - FNB
6.3.2.2 Water absorption Results of the changes in water absorption for the immersed specimens are presented in tables 30 to 32. Figure 46 shows the variation of water absorption with sodium hydroxide content. At 4% sodium hydroxide, water absorption is 10.92%, this slightly decrease to 10.59% when sodium hydroxide content is increased to 6%, from which it increases slightly to 10.63% when sodium hydroxide is increased to 8%, and finally increases to 10.87% at 10% sodium hydroxide.
Table 30, Variation of water absorption with NaOH content - FNB Series No. FNB7 FNB6 FNB2 FNB5
Ndofor Akongnui Fai
Average weight (g) W2 W3 45.23 50.17 45.33 50.13 45.83 50.70 46.27 51.30
Water absorption (%)
NaOH %
10.92 10.59 10.63 10.87
4.00 6.00 8.00 10.00
PHYLARES 2006
69 Variation of water absorption with NaOH content- FNB
water absorption (%)
11,0 10,9 10,8 10,7 10,6 10,5 10,4 4
6
8
10
% NaOH
Figure 46, Variation of water absorption with NaOH - content
From figure 47, water absorption by the immersed specimens increases from 10.27% at 20% water content to 10.63% at 22% water content It then falls to 9.86% at 24% water content after which it starts increasing again to 11.50% at 26% water. Table 31, Variation of water absorption with water content - FNB Series No. FNB3 FNB2 FNB4 FNB1
Average weight (g) W2 W3 44.77 49.37 45.83 50.70 44.63 49.03 44.87 50.03
Water absorption (%)
Water %
10.27 10.63 9.86 11.50
20.00 22.00 24.00 26.00
Variation of water absorption with water content - FNB
water absorption (%)
12,0 11,5 11,0 10,5 10,0 9,5 9,0 20
22
24
26
water content (%)
Figure 47, Variation of water absorption with water content - FNB
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PHYLARES 2006
70 From table 32 and figure 48, we observe that water absorption is higher for the samples with 150% sand than for those with 200% sand. FNB8 has water absorption of 11.04% while FNB2 has water absorption of 10.63%. Table 32, Variation of water absorption with sand content - FNB Series No. FNB8 FNB2
Average weight (g) W2 W3 44.1 48.97 45.83 50.7
Water absorption (%)
Sand %
11.04 10.63
150.00 200.00
Variation of water absorption with sand content - FNB
water absorption (%)
11,1 11,0 10,9 10,8 10,7 10,6 10,5 10,4 150
200 sand %
Figure 48, Variation of water absorption with sand content – FNB
6.3.3
Compressive strength and stability
The results of change of compressive strength under different conditions are shown in tables 33 to 35. Figure 49 represents the variation of compressive strength with sodium hydroxide content. For the dried specimens, compressive strength increases with an increase in sodium hydroxide content from 1.75MPa at 4% sodium hydroxide to a maximum of 5.53MPa at 8% sodium hydroxide. After 8% sodium hydroxide, we notice a slight decrease in the strength of the dried specimens and a slight increase for immersed and cycled specimens. The immersed and cycled specimens have more or less the same strengths and are about half those of dried specimens. The loss in strength due to immersion and cycling is quite reasonable, with average values of about 65% in both cases.
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PHYLARES 2006
71 Table 33, Variation of compressive strength with NaOH content - FNB Series No.
NaOH %
FNB7 FNB6 FNB2 FNB5
4.00 6.00 8.00 10.00
Compressive strength (MPa) S1 1.75 2.40 5.53 5.13
S2 0.53 0.68 1.83 2.27
Loss of strength (%)
S3 0.49 0.77 1.97 2.10
L1 69.71 71.67 66.91 55.75
L2 72.00 67.92 64.38 59.06
compressive strength (MPa)
Variation of compressive strength with % NaOH - FNB 6 5 4
S1, dried specimens S2, immersed specimens S3, cycled specimens
3 2 1 0 4
6
8
10
% NaOH
Figure 49, Variation of compressive strength with NaOH content – FNB
From figure 50, we observe that at 20% water content, compressive strength of dried specimens is 4.27MPa. It increases to 5.53MPa at 22% water, after which it starts falling. For the immersed and cycled specimens, compressive strength decreases with increase in water content, with maximum values at 20% water and minimum at 26% water. This tells us there should be some components which absorb water and maybe swell leaving a lot of pore spaces in the material. Table 34, Variation of compressive strength with water content - FNB Series No.
water %
FNB3 FNB2 FNB4 FNB1
20.00 22.00 24.00 26.00
Ndofor Akongnui Fai
Compressive strength (MPa) S1 4.27 5.53 4.3 3.20
S2 2.53 1.83 1.6 0.90
S3 2.43 1.97 1.7 1.00
Loss of strength (%) L1 40.75 66.91 62.79 71.88
L2 43.09 64.38 60.47 68.75
PHYLARES 2006
72 Variation of compressive strength with water content - FNB
compressive strength (MPa)
6 5 4
S1, dried specimens S2, immersed specimens S3, cycled specimens
3 2 1 0 20
22
24
26
water content (%)
Figure 50, Variation of compressive strength with water content – FNB
From table 35 and figure 51, the compressive strengths under all conditions for the samples with 200% sand are more than double those for specimens with 150% sand.
Table 35, Variation of compressive strength with sand content - FNB Series No.
Sand %
FNB8 FNB2
150 200
Compressive strength (MPa) S1 1.53 5.53
S2 0.6 1.83
S3 0.53 1.97
Loss of strength (%) L1 60.78 66.91
L2 65.36 64.38
Variation of compressive strength with sand content - FNB
compressive strength (MPa)
6 5 4 150% sand
3
200% sand
2 1 0 S1
S2
S3
Figure 51, Variation of compressive strength with sand content – FNB
Ndofor Akongnui Fai
PHYLARES 2006
73 The compressive strengths obtained from FNB5 under dried, immersed and cycled conditions were 5.13MPa, 2.27MPa and 2.1MPa respectively, while for FNB2 we had 5.53MPa, 1.83Mpa, and 1.97MPa respectively. Average loss in strengths due to immersion and cycling for FNB5 was about 57% and for FNB2 about 65%. These two series thus gave the best results in terms of compressive strengths with FNB5 slightly better than FNB2. The densities of the 2 series of specimens were not very much different. FNB2 had water absorption after immersion of 10.63% while FNB5 had 10.87%. Putting all these properties together and looking at cost of production, a sample with 8% sodium hydroxide will be better of than that with 10% sodium hydroxide. At 10% sodium hydroxide, there is a possibility of excess un-reacted sodium hydroxide stay in the material which causes degradation with time.
6.3.4
Efflorescence
All specimens that were half immersed in water showed little efflorescence, usually after about 1 week. The material deposited at the upper surfaces was rust like. Leaching was quite prominent during the first three days of immersion. The water usually became reddish brown in color, which indicated the disintegration of the material. After changing the water and washing the some samples twice usually after one week, leaching stopped. The specimen as a whole usually shows some sort of degradation after about 3 weeks. pH of the water after 4 hours was usually about 12, but decreased to about 7 after two months generally for all the series.
6.4 Nkolbison sample, (FNK) Eleven series of specimens with different compositions were prepared. We started by verifying the required composition by weight of water with respect to that of the soil. Using a sodium hydroxide content of 8%, the first three specimens gave very low compressive strengths. We decided to raise the sodium hydroxide content to 12% in series FNK4 and this resulted in encouraging results. With 12% sodium hydroxide content, the water content was then optimized before we checked the sand content. Table 36 shows the composition by weight and the percentage by weight of the various components for each series of specimens.
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PHYLARES 2006
74 Table 36, Composition for each series of specimens - FNK Series No. FNK1 FNK2 FNK3 FNK4 FNK5 FNK6 FNK7 FNK8 FNK9 FNK10 FNK11
6.4.1
Clay (g) 153.0 154.0 153.6 151.1 150.2 149.3 151.1 152.0 149.3 176.7 214.6
Composition by Weight for Filler (sand) NaOH (g) (g) 306.0 12.2 309.0 12.3 307.2 12.3 302.1 18.1 300.4 18.0 298.5 17.9 302.1 15.1 304.0 12.2 298.5 20.9 265.0 21.2 214.6 25.8
Water (g) 29.0 24.7 26.9 28.7 31.5 34.3 31.7 31.9 31.3 37.1 45.1
Total Weight (g) 500 500 500 500 500 500 500 500 500 500 500
Percentage by Weight of Clay Filler NaOH (%) (%) (%) 100 200 8 100 200 8 100 200 8 100 200 12 100 200 12 100 200 12 100 200 10 100 200 8 100 200 14 100 150 12 100 100 12
water (%) 19 16 17.5 19 21 23 21 21 21 21 21
Fabrication of Specimens
After the first three series of specimens were prepared and tested for compressive strength, we almost abandoned the sample because of the very low compressive strengths obtained. The sodium hydroxide content was then raised to 12% in the fourth series, from which the results were encouraging. The first series FNK1 had a water content of 19% which is slightly below the plastic limit. The workability was not quite good. We decided to reduce the water content in series FNK2 to 16%, but it was dry and compaction not good. However after increasing the sodium hydroxide content to 12%, we realized that with 19% water the mixture was dry and not easily compacted. Raising water content to 21% gave good workability and compaction. At 23% water, workability was poor as the material could not be well mixed and sticking to the walls of the mixer and on the mixing arm. At optimum water contents, if we increase the sand content, this resulted in good workability, while reducing sand content resulted in poor workability like in the case of FNK11 whereby the sand content is same as soil content. It was observed that the best means of adding the sodium hydroxide solution and water was bit by bit while the mixer is mixing the soil/sand mixture at speed 1. This was implemented from FNK3 to FNK11.
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PHYLARES 2006
75 6.4.2
Physical Characteristics of Specimens
6.4.2.1 Density The highest densities were observed after moulding. They decreased from about 6.68% in FNK2 to 13.58% in FNK11 after the specimens were cured. After post curing, the densities of the dry samples kept at 40°C also changed slightly from those obtained after curing, ranging from -0.22% in FNK1 to 1.74% in FNK5. Results presented in tables 37 to 39 show that changing the proportion of various components resulted in a change of density. The variation of density with percentage sodium hydroxide for specimens having same water and sand content is shown in figure 52. The general trend shows an increase in density when amount sodium hydroxide is increased though we have a slight decrease at 12% sodium hydroxide. The least densities are thus observed at 8% sodium hydroxide for all three groups of specimens and the highest at 14% sodium hydroxide. Table 37, Variation of density with NaOH content - FNK Series No. d1 2.054 2.114 2.081 2.123
FNK8 FNK7 FNK5 FNK9
Average density (g/cm3) d2 1.894 1.923 1.902 1.935
Change in density (%) d1 d2 8.45 0.37 9.93 0.57 9.41 1.74 9.72 7.86
d3 1.901 1.934 1.935 2.087
Percentage by weight NaOH (%) 8.00 10.00 12.00 14.00
Variation of density with % NaOH - FNK 2,15
density (g/cm3)
2,1 2,05
af ter moulding
2
af ter curing
1,95
dried specimens af ter post curing
1,9 1,85 1,8 1,75 8
10
12
14
% NaOH
Figure 52, Variation of density with NaOH content – FNK
Ndofor Akongnui Fai
PHYLARES 2006
76 From figure 53, density varies when water content is varied. Density after moulding increases from 2.01g/cm3 at 19% water to 2.098g/cm3 at 23% water. Looking at figure 52, the cycled specimens optimum density is 1.935g/cm3 which is obtained at 21% water. We then decided to choose 21% water as optimum for this sample, coupled with the fact that workability at 21% was also better than at 23% and water absorption not too different.
Table 38, Variation of density with water content - FNK Series No. FNK4 FNK5 FNK6
Average density (g/cm3) d1 d2 d3 2.01 1.859 1.884 2.081 1.902 1.935 2.098 1.916 1.929
Change in density (%) d1 d2 8.12 1.34 9.41 1.74 9.50 0.68
Percentage by weight water (%) 19.00 21.00 23.00
Variation of density with water content at 12% NaOH - FNK 2,15
density (g/cm3)
2,1 2,05
af ter moulding
2
af ter curing
1,95 1,9
dried specimens af ter post curing
1,85 1,8 1,75 1,7 19
21
23
water content (%)
Figure 53, Variation of density with water content – FNK
We observe from figure 54 that density varies with sand content. At a sand content of 100%, we have the highest densities after moulding, curing and post curing. The densities decrease with increase in sand content. A sand content having same weight as the soil content is therefore the best for this sample.
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PHYLARES 2006
77
Table 39, Variation of density with sand content - FNK Series N°.
Average density (g/cm3) d1 d2 d3 2.266 1.995 2.021 2.207 1.996 2.027 2.081 1.902 1.935
FNK11 FNK10 FNK5
Percentage by weight sand (%) 100 150 200
Change in density (%) d1 d2 13.58 1.30 10.57 1.55 9.41 1.74
Variation of density with sand content - FNK 2.3 2.2 2.1
after moulding
2
after curing dried specimens after postcuring
1.9 1.8 1.7 100
150
200
sand content (%)
Figure 54, Variation of density with sand content - FNK
6.4.2.2 Water absorption Results of the changes in water absorption for the immersed specimens are presented in tables 40 to 42. Figure 55 shows the variation of water absorption with sodium hydroxide content. At 8% sodium hydroxide, water absorption is 12.44%, this decrease to 11.42% when sodium hydroxide content is increased to 10%, from which it increases slightly to 11.82% when sodium hydroxide is increased to 12%, and finally increases to 14.78% at 14% sodium hydroxide. Ideal sodium hydroxide contents should thus range from 10 to 12% in order, to minimize water absorption.
Table 40, Variation of water absorption with NaOH content - FNK Series No. FNK8 FNK7 FNK5 FNK9
Ndofor Akongnui Fai
Average weight (g) W2 W3 46.4 52.17 46.67 52.00 45.43 50.80 42.43 48.70
Water absorption (%)
NaOH %
12.44 11.42 11.82 14.78
8.00 10.00 12.00 14.00
PHYLARES 2006
78
Variation of water absorption with NaOH content - FNK
water absorption (%)
16 14 12 10 8 6 4 2 0 8
10
12
14
% NaOH
Figure 55, Variation of water absorption with NaOH content - FNK
From figure 56, water absorbed by immersed specimens decreases with an increase in water content from 12.08% at 19% water content to 11.25% at 23% water content. With an understanding that the optimum water content is somewhere between 21 and 23%, after 23%, we will expect an increase in water absorption. Table 41, Variation of water absorption with water content - FNK Series No. FNK4 FNK5 FNK6
Average weight (g) W2 W3 46.60 52.23 45.43 50.80 46.47 51.70
Water absorption (%)
Water %
12.08 11.82 11.25
19.00 21.00 23.00
variation of water absorption with water content - FNK
water absorption (%)
12,2 12,0 11,8 11,6 11,4 11,2 11,0 10,8 19
21
23
water content (%)
Figure 56, Variation of water absorption with water content - FNK
Ndofor Akongnui Fai
PHYLARES 2006
79 Figure 57 shows the relationship between sand content and water absorption. At a sand content of 150%, we have the least water absorption after immersion which is 9.77%. This relates very well with the density results obtained. At a sand content of 200%, we have the highest water absorption which is 11.82%.
Table 42, Variation of water absorption with sand content - FNK Series No. FNK11 FNK10 FNK5
Average weight (g) W2 W3 44.38 48.87 45.67 50.13 45.43 50.80
Water absorption (%)
Sand %
10.12 9.77 11.82
100.00 150.00 200.00
Variation of water absorption with sand content - FNK
water absorption (%)
14 12 10 8 6 4 2 0 100
150
200
sand %
Figure 57, Variation of water absorption with sand content – FNK
6.4.3
Compressive strength and stability
The results of change of compressive strength under different conditions are shown in tables 43 to 45. Figure 58 represents the variation of compressive strength with sodium hydroxide content for samples having a sand content of 200%. For the dried specimens, compressive strength increases with an increase in sodium hydroxide content from 5.7MPa at 8% sodium hydroxide to a maximum of 13.4MPa at 12% sodium hydroxide. After 12% sodium hydroxide, we notice a decrease in compressive strength for all groups of specimens. The decrease in strength is quite remarkable when we increase sodium hydroxide content from 12 to 14%. This tells us that after 12% sodium hydroxide, the excess un- reacted sodium hydroxide in the material has a negative Ndofor Akongnui Fai
PHYLARES 2006
80 effect in the materials strength, with a high amount of degradation experienced. The immersed and cycled specimens have more or less the same strengths and are about half that of dried specimens. The loss in strength due to immersion and cycling is quite reasonable, with average values of about 58%. Table 43, Variation of compressive strength with NaOH content - FNK Series No.
NaOH %
FNK8 FNK7 FNK5 FNK9
8.00 10.00 12.00 14.00
Compressive strength (Mpa) S1 5.7 8.43 13.4 6.87
S2 2.33 3.4 5.93 3.13
S3 2.57 3.5 5.33 2.87
Loss of strength (%) L1 59.12 59.67 55.75 54.44
L2 54.91 58.48 60.22 58.22
compressive strength (MPa)
Variation of compressive strength with % NaOH - FNK 16 14 12 10
S1 dried specimens
8 6
S2 immersed specimens
4
S3 cycled specimens
2 0 8
10
12
14
% NaOH
Figure 58, Variation of compressive strength with NaOH content – FNK
From figure 59, we observe that 19% water content, compressive strength of dried specimens is 6.43MPa and increases to 13.63MPa at 23% water. For the immersed and cycled specimens, compressive strength also increases with increase in water content, with maximum values at 21% water, after which they start falling, this being one of the reasons why we think 21% is the optimum water content.
Ndofor Akongnui Fai
PHYLARES 2006
81 Table 44, Variation of compressive strength with water content - FNK Series No.
water %
FNK4 FNK5 FNK6
19.00 21.00 23.00
Compressive strength (Mpa) S1 6.43 13.4 13.63
S2 2.5 5.93 5.17
Loss of strength (%)
S3 2.8 5.33 4.83
L1 61.12 55.75 62.07
L2 56.45 60.22 64.56
Variation of compressive strength with water content - FNK
compressive strength (MPa)
16 14 12 10
S1 dried specimens
8
S2 immersed specimens S3 cycled specimens
6 4 2 0 19
21
23
water content (%)
Figure 59, Variation of compressive strength with water content - FNK
Changes in sand content bring about very remarkable changes in the compressive strength of this sample. From figure 60, we observe that at a soil/sand ratio of 1:1, the compressive strengths are 21.03MPa, 9.03MPa and 8.50MPa for the dried, immersed and cycled specimens respectively. At a sand soil ratio of 2:1, we have the least strengths under all conditions. At a sand/soil ratio of 3/2:1, we have the highest compressive strengths which are 24.97MPa, 9.80MPa and 9.37MPa under dried, immersed and cycled conditions respectively. A sand content of 150% thus results in the best packing and density surely. Table 45, Variation of compressive strength with sand content - FNK Series No.
sand %
FNK11 FNK10 FNK5
100.00 150.00 200.00
Ndofor Akongnui Fai
Compressive strength (MPa) S1 21.03 24.97 13.4
S2 9.03 9.80 5.93
S3 8.50 9.37 5.33
Loss of strength (%) L1 L2 57.06 59.58 60.75 62.47 55.75 60.22
PHYLARES 2006
82
compressive strength (MPa)
Variation of compressive strength with sand content - FNK 30 25 20
S1 dried specimens
15
S2 immersed specimens S3 cycled specimens
10 5 0 100
150
200
sand %
Figure 60, Variation of compressive strength with sand content – FNK
The sodium hydroxide content which gave us the best compressive strengths, optimum densities and the least water absorption was 12% as shown by the properties of series FNK5 and FNK6. At 8% sodium hydroxide, as stated before we almost forgot about this sample. At 10% sodium hydroxide, the results were not better than what we had at 12% and finally at 14% sodium hydroxide, we instead had compressive strengths about 50% less than those obtained at 12% sodium hydroxide. At 14% sodium hydroxide, which is series FNK9, water absorption was 14.78% being the highest obtained. This water absorption can be linked to excess un-reacted sodium hydroxide in the material. Excess sodium hydroxide reacts with carbondioxide to produce sodium carbonate which is hygroscopic and so absorbs more water and also increases fissures and voids in the material. This is probably what resulted in the low strengths of these specimens. Normally water weakens a material, the more water we have in a material the lower its strength since this water serves as a lubricant making it easy for grains to be sliding against each other. Variation of sand content gave rise to remarkable results. At a sand/soil ratio of 3/2:1 with same water and sodium hydroxide contents, the compressive strengths were almost double what we had at a sand soil ratio of 2:1.
6.4.4
Efflorescence
The half immersed specimens of series FNK1 to FNK8 showed little efflorescence, usually after about 10 days. For series FNK9 to FNK11, efflorescence was quite prominent. The material deposited at the upper surfaces looked rust-like. Leaching was quite prominent during the first
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83 three days of immersion. The water usually became yellowish-brown in color, which indicated disintegration of the material especially for series FNK1 to FNK3, FNK7 and FNK8. The specimens showed some sort of degradation after about 4 weeks. The degradation of series FNK9 started less than 2 weeks after immersion. pH of the water after 4 hours was usually about 11 to 12.5, but decreased to 7 to 7.5 after two months.
6.5 Changing the maximum grain size of soil samples Unlike samples of the other series which had a maximum grain size of 425µm , those of series FBM10 and FBM11 had as maximum grain size 106µm and 212µm respectively. This variation in grain size resulted in changes in the physical and mechanical properties of the materials. 6.5.1
Physical Characteristics of Specimens
6.5.1.1 Density From table 46 and figure 61, we observe some changes in density with an increase in grain size. From 106µm to 212µm, we observe a decrease in density of about 0.3%. From 212µm to 425µm, we observe an increase of 0.5%. The densities at 425µm are the highest obtained under all conditions. The fall in density after curing for maximum grain sizes 425µm is 10.98% which is the smallest. Change in density after post curing for the dried specimens is least at 212µm. The general observation from figure 60 is that there are no significant changes in density under all conditions when grain size was varied. Table 46, Variation of density with grain size - FBM Series No. FBM10 FBM11 FBM4
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Average density (g/cm3) d1 d2 d3 2.107 1.897 1.891 2.101 1.889 1.89 2.112 1.903 1.913
Change in density (%) d1 d2 11.07 -0.32 11.22 0.05 10.98 0.53
Maximum grain size µm 106.00 212.00 425.00
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84 Variation of density with grain size 2,15
density (g/cm3)
2,1 2,05 2
after moulding
1,95
after curing
1,9
dried specimens after post curing
1,85 1,8 1,75 106
212
425
max grain size (um)
Figure 61, Variation of density with grain size – FBM
6.5.1.2 Water absorption From table 47 and figure 62, there was an increase in water absorption of about 8.4% when maximum grain size was increased from 106µm to 212µm. From 212µm to 425µm, water absorption decreased by about 13%. This maybe attributed to the fact that there are some swelling clays in the sample which absorb more water. These clays are finer than kaolinite and will thus dominate the fine grain portion of the soil sample.
Table 47, Variation of water absorption with grain size - FBM Series No. FBM10 FBM11 FBM4
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Average weight (g) W2 W3 44.75 50.4 43.5 49.5 45.6 51.07
Water absorption (%) 12.63 13.79 12.00
Maximum grain size µm 106.00 212.00 425.00
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85 Variation of water absorption with grain size
water absorption (%)
14,0 13,5 13,0 12,5 12,0 11,5 11,0 106
212
425
max griansize (um)
Figure 62, Variation of water absorption with grain size – FBM
6.5.2
Compressive strength and Stability
From table 48 and figure 63, we observe a general trend which is a decrease in compressive strength with an increase in maximum grain size. However we observe a slight anomaly at for the immersed and cycled specimens at maximum grain size 212µm. Loss in strength due to immersion and cycling is least at a maximum grain size of 425µm and highest at 212µm this relates very well with the water absorption. The more the water absorbed the more the loss in strength. Table 48, Variation of compressive strength with grain size - FBM Series No.
Maximum grain size (µm)
FBM10 FBM11 FBM4
106.00 212.00 425.00
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Compressive strength (Mpa) S1 13.65 12.5 10.93
S2 7.4 6.3 6.37
S3 7.7 6.1 6.53
Loss of strength (%) L1 L2 45.79 43.59 49.60 51.20 41.72 40.26
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86 Variation of compressive strength with grain size - FBM
compressive strength (MPa)
16 14 12 10
S1 dried
8
S2 immersed
6
S3 cycled
4 2 0 106
212
425
max grain size (um)
Figure 63, Variation of compressive strength with grain size – FBM
Changing maximum grain size of the FBM sample did not result in very remarkable changes in the density of the specimens under all conditions. However we noticed that a change in maximum grain size from 106µm to 425µm resulted in a 19.9% increase in the compressive strength of the dry specimens. We also observed a similar increase in the immersed and cycled specimens. The loss in strength instead increases when we decrease grain size. The increase in strength can be attributed to the increase surface area for reactions which give rise to more stable materials to occur when we have finer grains. So in order to have better results in terms of compressive strength, it is preferable to crush the materials to very fine grains.
6.6 Influence of curing temperature Specimens FBM13-1, FBM13-2 and FBM13-3 were cured at 60°C, FBM13-4, FBM13-5 and FBM13-6 at 105°C while FBM13-7 to FBM13-10 was cured at 130°C. These specimens were all kept in an oven set at 40°C after curing or ten days after which then were tested for compressive strength. The results obtained including those of the dried specimens of series FBM4 were compared to determine the effects of curing temperature on the physical and mechanical properties. 6.6.1
Influence of curing temperature on density
We realize from table 49 and figure 64 that there is only a slight variation in density as a result of change in curing temperature. Looking carefully at the results, we observe that the highest
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87 densities are obtained at 80°C. None of the specimens was immersed so we can not talk about water absorption. Table 49, Variation of density with curing temperature - FBM Temperature (°C) 60 80 105 130
after moulding 2.084 2.103 2.089 2.099
Density (g/cm3) after after post curing curing 1.897 1.902 1.906 1.910 1.878 1.889 1.887 1.898
Variation of density with curing temperature 2,15
densty(g/cm3)
2,1 2,05 2
after moulding after curing
1,95
after post curing
1,9 1,85 1,8 1,75 60°C
80°C
105°C
130°C
temperature (°C)
Figure 64, Variation of density with curing temperature - FBM
6.6.2
Compressive strength and stability
Compressive strength is also affected by curing temperature as shown in table 50 and figure 65. From a temperature of 60°C to 80°C, we observe a slight increase in compressive strength of about 3%. Looking at the strengths at 80°C and 130°C, the difference is not too much. This means at a curing temperature range from 60°C to 130°C, we will have almost the same strengths. In order to economize energy and limit environmental degradation, we have to work at a temperature of about 80°C. Table 50, Variation of compressive strength with curing temperature - FBM Temperature (°C) 60°C 80°C 105°C 130°C
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Compressive Strength (MPa) 13.3 13.7 12.2 11.6
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88
compressive strength (MPa)
Variation of compressive strength with curing temperature 14 13,5 13 12,5 12 11,5 11 10,5 60°C
80°C
105°C
130°C
curing temperature (°C)
Figure 65, Variation of compressive strength with curing temperature – FBM
Different specimens of series FBM13 cured under different temperatures and all kept in an oven for 10 days before testing for compressive strength had almost the same densities. Curing temperature therefore had no big influence in the densities of the specimens. What was influenced by curing temperature was compressive strength. A general decrease in compressive strength was observed with an increase in temperature. At 60°C, we had a compressive strength of 13.3MPa and at 130°C we had a compressive strength of 11.6MPa corresponding to a decrease in compressive strength of 12.8%. In terms of stability, those cured at 80°C gave the best stability. Ideal curing temperatures should therefore lie between 75°C and 85°C. Increasing curing temperatures will instead result in materials with a low strength and low stability
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Chapter-7
Conclusions and Recommendations
7.1 Specifications for the use of soils in construction The compressive strength of construction materials is perhaps their most important property. It is the wet compressive strength value that is used for the structural design of buildings. Soil-based building materials should have wet compressive strengths ranging from 1.0MPa minimum for dry arid regions to 2.8MPa minimum for wet regions (ILO, 1987). For soil blocks, the U.S. Department for Housing and Urban development (USDHUD, 1955) [38] proposes average dry compressive strengths of 2.1MPa with 1.8MPa as absolute minimum. The British Standard requirements (BS 2028) specifies that dry compressive strengths under load bearing conditions for bricks in private or rural dwellings should be at least 5.2MPa. Spence and Cook (1983) [39], talk of an average range of 3.0-3.5MPa for load bearing requirements of normal two-story buildings. Due to the high compressive pressures (15MPa) used to make the samples; all of them seem to give strengths which meet up with all sited specifications. Under normal working conditions, blocks for walls for example will be produced at far lesser compressive pressures, so not all these samples meet up with the specifications. The influence of moisture on the durability of these materials makes water absorption a very important characteristic for soil-based construction materials. The recommended maximum water absorption value is 15% (ILO, 1987). Houben et al (1996) proposed maximum water absorption of 20%. In the next sections, we are going to compare the results obtained from the samples and these specifications to see if the samples can be used as precursors for construction materials. After producing different series of materials specimens from the soil samples, we looked at their physical and mechanical properties to help us achieve our objectives. The collection of the four samples was done based on not too exact data from MIPROMALO, which obviously lead to too many assumptions and so probable errors. Due to the limitations we had in the identification and sampling processes, the results we obtained should only help as a guide for future detailed work in this light. Interpretation of results obtained has not been quite easy as we did not carry out
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90 mineralogical and chemical analysis of these samples. If we knew the exact composition of each sample, then we could say with a lot of certainty how the physical and chemical properties they have come about. With these limitations, we will try to assess the various characteristics showed by these samples and conclude if they can be used as precursors for construction materials.
7.2 Mvog Betsi sample, (FET) With a constant compaction pressure of 15MPa, we observed an increase in both dry and wet compressive strength for sample FET up to a maximum of 8% sodium hydroxide. At 4% sodium hydroxide content we had dry and wet compressive strengths of 3MPa and 0.5MPa respectively, while at 8% sodium hydroxide we had 7MPa and 3MPa respectively. This represents an increase of about 56% for the dry strengths and 83% for the wet strengths. We have water absorptions ranging from 10 to 12% for all the series in FET. Even though the compressive strengths are well above the recommended minimum while the water absorptions are below the maximum recommended, this sample cannot be recommended for use as a precursor for construction materials when stabilized by adding sodium hydroxide. This is because the strengths obtained are not quite reasonable when we take into consideration the high compaction pressures which are never attained in practice. The low compressive strengths obtained for this sample maybe because of the presence of other types of clays or colloidal material based on its high plasticity, high content of materials finer than kaolinite and high loss on ignition below 500°C.
7.3 Bambili sample, (FBM) The dry compressive strength increased from 5MPa to 12MPa by increasing the sodium hydroxide content from 4% to 8% representing a 58% increase, while the wet compressive strength increased from 2MPa to 7MPa representing a 71% increase. The loss of strength due to cycling and immersion decreased from an average of about 58% to 41%, representing an average decrease of 31% when sodium hydroxide was increased from 4% to 8%. Water absorption decreased due to the increase in sodium hydroxide content and varied from 12 to 16%. The compressive strength values are well above the minimum recommended while the water absorption is below the maximum recommended. These results can be acceptable despite the high compaction pressures for they fall around the limits. We can recommend it for use as a precursor to construction materials when stabilized by adding sodium hydroxide. The only Ndofor Akongnui Fai
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91 problem we have is because the strengths given by the cycled specimens are not quite satisfactory which has to be taken seriously. We need to do a more detailed study of mineralogy and chemical composition of soils from this area and we will be sure to get samples that will give us very satisfactory results using the mineral polymerization technique. FBM4 gives us the best results amongst all the series of samples. Its optimized ratio of soil/sand/NaOH/water which is 100:200:8:28 can be adopted for this sample for future works.
7.4 Simbock sample, (FNB) The optimized ratio for sand/soil/NaOH/water for this sample which gave the best results is 100:200:8:22. At 4% sodium hydroxide content we obtained dry and wet compressive strengths of 2MPa and 0.5MPa respectively. While at 8% sodium hydroxide content, we obtained 5MPa and 2MPa respectively representing an average increase of about 60% for the dry specimens and 75% for wet specimens. Loss of compressive strength due to cycling and immersion experienced about a 7% reduction due to the increase in sodium hydroxide content from 4 to 8%. Water absorption decreased due to the increase in sodium hydroxide content varying from 10 to 12%. These water absorptions meet up with specifications. The compressive strengths are above those recommended but still low for the sample to be considered as a precursor for construction materials when stabilized with the mineral polymerization technique considering the high compaction pressures that were used in making the samples. This soil is not a good precursor for construction materials using the mineral polymerization technique. This might be attributed to the presence of a high amount of organic matter and/or other kinds of clays or colloidal materials which react with sodium hydroxide but the reaction does not result in materials that give high strengths like kaolinite does. Results of granulometric analysis and loss on ignition confirm this. The high plasticity limit for this soil does not match with that of standard kaolinite, also suggesting the presence of undesired components in the soil.
7.5 Nkolbison sample, (FNK) At a sand soil ratio of 2:1 and sodium hydroxide content of 8%, we had dry and wet compressive strengths of 6MPa and 3MPa respectively. At same sand/soil ratio and a sodium hydroxide content of 12%, we had dry and wet compressive strengths of 13MPa and 6MPa respectively, representing an increase of about 50% in both cases. At a sand/soil ratio of 3/2:1 and a sodium Ndofor Akongnui Fai
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92 hydroxide content of 12%, we obtained dry and wet compressive strengths of 25MPa and 10MPa respectively, representing an increase of about 48% and 40% respectively when compared to that with a sand/soil ratio of 2:1. The loss in compressive strength due to cycling and immersion in water are averagely 60%. Water absorption ranges from 10% in FNK10 to 15% in FNK9. The compressive strengths obtained are far above the minimum recommended while the water absorption is below the recommended maximum. The composition of FNK10 will thus be the one to be adopted for the FNK sample. The optimized ratio retained for this sample of soil/sand/NaOH/water is 100:150:12:21, which is that of FNK10. From the physical and mechanical properties obtained, we can say with certainty that this soil can be used as a precursor for construction materials when stabilized with the mineral polymerization technique.
7.6 Changing the maximum grain size of soil samples Soils with small maximum grain sizes, say <106µm result in materials with better compressive strengths and stability. Hence it is advisable to crush soils to very fine grains before stabilizing them using the mineral polymerization technique
7.7 Influence of curing temperature High curing temperatures result in lower or almost the same strengths and stability. Ideal curing temperatures should fall between 75°C and 85°C.
7.8 Sodium hydroxide as stabilizing argent Observing the changes in the physical and mechanical properties of the materials as we vary the amount of sodium hydroxide in them makes us conclude that sodium hydroxide can be used for stabilizing them. This is supported by the fact that specimens of series FBM12 which had no sodium hydroxide were not stable at all when immersed in water. They completely disintegrated when put in water after curing. With 4% sodium hydroxide, specimens were quite stable in water. Upon increasing sodium hydroxide, we had remarkable increases in compressive strength. At 0% sodium hydroxide we had averagely 0.5MPa as compressive strengths for the dried specimens while at 8% sodium hydroxide, an increase in compressive strength of about 95% was observed. We just need to look for the right specimens that are suitable for the mineral Ndofor Akongnui Fai
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93 polymerization technique; optimize the water, sand and sodium hydroxide content and this will result in good construction materials.
7.9 Recommendations 1. Sampling should be guided by mineralogical and chemical analysis. This will help us avoid wasting time and resources over samples that will end up giving poor results. 2. With a complete mineralogical and chemical analysis of samples, we can be able to determine how the quantity of kaolinite influences the properties of the materials. This can help us reduce cost.
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95 [13] Van Ranst, E., Soil mineralogy course notes, Laboratory of soil science, Ghent University, (1997) [14] Sherwood, P.T., Soil stabilization with cement and lime state-of-the-art review. Transport and research laboratory, Her majesty’s Office London, (1993). [15] Bell, F.G., Lime stabilization of clay minerals and soils. Engineering geology, vol 42,4,(1996) pp 223-237 [16] Al-Rawas, A.A., Hago, A.W. & Al-Sarmi, H., Effect of lime, cement and Sarooj (artificial pozzolan) on the swelling potential of an expansive soil from Oman. Construction and building materials vol 40, 5, (2005) pp681-687 [17] Temimi, M., Amor, K.B. & Camps, J.P., Making building products by extrusion and cement stabilization: limits of the process with montmorillonitic clay. Applied science, vol 13, 4, (1998) pp 245-253 [18] Osula, D.O.A., A comparative evaluation of cement and lime modification of laterite. Engineering geology, vol 42, 1, (1996) pp 71-81 [19] Bruce, D.W. Bruce and D. O’Hare (Editors), Inorganic Materials; Wiley: New York 1992 [20] Boulet, P., Greenwell, H.C., Stackhouse, S. and Coveney, P.V., Recent advances in understanding the structure and reactivity of clays using electronic structure calculations. Molecular structure: THEOCHEM (2006), Issues 1- 3, pages 33-48 [21] Terence H. Coopers and Regents, 2000, Soil science 702/802: Chemistry of soils syllabus (revised Jan 1998) [22] Gualtieri, A. and Belloto, M., Modeling the structure of the metastable phases in the reaction sequence kaolinite – mullite by x-ray scattering experiments. Physics and chemistry of minerals (1998), Volume 25 – 6, page 442 – 452 [23] Stevenson, M. and Sagoe-Crentsil, K., Relationships between composition, structure and strength of inorganic polymers: Part 1; Metakaolin-derived inorganic polymers. Materials science volume 40,number 8 (2005) page 2023-2036 [24] Ronald D. Archer, Inorganic and organometallic polymers. John Wiley and sons (2001), 264 pages. [25] Van Jaarsveld, J.G.S., Van Deventer, J.S.J. and Lorenzen, L., Met. Mater. Trans. B29B (1998), 283
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97 [38] USDHUD (U.S. Department of Housing and Urban development), (1955), Earth and Homes. Ideas and Methods Exchange N°22, Office of International Affairs, USDHUD [39] Spence, R.J.S. and Cook, D.J., (1983). Building materials in developing countries. John Wiley and Sons, Chichester, England.
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