GEOPOLYMER CONCRETE REPORT:
1.0 ABSTRACT Cement is the world's most adaptable, strong and solid development material. By water, cement is the most utilized material, which required expansive amounts of Portland cement. Conventional Portland cement generation is the second just to the vehicles as the significant generator of carbon di oxide, which dirtied the air. Notwithstanding that huge sum vitality was likewise devoured for the bond creation. Subsequently, it is unavoidable to locate an option material to the current most costly, most asset expending Portland cement. The consumption of Ordinary Portland Cement (OPC) caused pollution to the environment due to the emission of CO2. As such, alternative material had been introduced to replace OPC in the concrete. Geopolymer cement is a creative development material which might be delivered by the compound activity of inorganic particles. Fly Ash, a by-result of coal got from the warm power plant is bounty accessible around the world. Fly ash is rich in silica and alumina responded with soluble arrangement delivered aluminosilicate gel that gone about as the coupling material for the solid. The compressive strength increases with the increasing of fly ash fineness and thus the reduction in porosity can be obtained. Fly ash based geopolymer also provided better resistance against aggressive environment and elevated temperature compared to normal concrete. As a conclusion, the properties of fly ash-based geopolymer are enhanced with few factors that influence its performance. This paper tends to explain constituents of Geo-polymer concrete, its quality and potential applications.
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2.0 INTRODUCTION The major problem that the world is facing today is the environmental pollution. In the construction industry mainly the production of ordinary Portland cement (OPC) will cause the emission of pollutants which results in environmental pollution. Cement production is growing by 2.5% annually, and is expected to rise from 2.55 billion tons in 2006 to 3.7-4.4 billion tons by 2050.The emission of carbon dioxide during the production of ordinary Portland cement is tremendous because the production of one ton of Portland cement emits approximately one ton of CO2 into the atmosphere. On the other hand, the climate change due to global warming, one of the greatest environmental issues has become a major concern during the last decade. The global warming is caused by the emission of greenhouse gases, such as CO2, to the atmosphere by human activities.
Although the use of Portland cement is still unavoidable until the foreseeable future, many efforts are being made in order to reduce the use of Portland cement in concrete. These efforts include the utilisation of supplementary cementing materials such as fly ash, silica fume, granulated blast furnace slag, rice-husk ash and finding alternative binders to Portland cement.In this aspect, the geopolymer technology proposed by Davidovits (1988a; 1988b) shows considerable promise for application in concrete industry as an alternative binder to the Portland cement. The role of binder in geopolymer concrete is replaced by fly ash which also possess pozzolanic properties as OPC and rich with alumina and silicate. Fly ash is residue from the combustion of coal which is widely available worldwide and lead to waste management proposal. Hence, fly ash-based geopolymer concrete is a good alternative to overcome the abundant of fly ash.
In fly ash-based geopolymer concrete, the silica and the alumina present in the source materials are first induced by alkaline activators to form a gel known as aluminosilicate. This gel binds the loose aggregates and other unreacted materials in the mixture to form the geopolymer concrete (Wallah, 2009). Besides that, the reaction also depends on a few parameters such as size of aggregates, chemical composition of fly ash, amount of vitreous phase in fly ash, nature, concentration and pH of activators. The curing process of geopolymer concrete play shows a great influence on the development of microstructure, and subsequently on the mechanical characteristics of geopolymer.
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3.0 LITERATURE REVIEW 1) L. Krishnan et al (2014). The objective of this research work was to produce a carbon dioxide emission free cementious material. In this research main limitations of fly ash based geopolymer concrete i.e. i. slow setting of concrete at ambient temperature, ii. the necessity of heat curing are eliminated by addition of Ground Granulated Blast Furnace Slag (GGBS) powder. The Alkaline liquids used in this study for the polymerization process are the solutions of sodium hydroxide (NaoH) and sodium silicate (Na2Sio3). The cube compressive strength was calculated for 12M solution for different mix Id i.e. F90G10, F80G20, F70G30, and F60G40 (Where F and G are, respectively, Fly Ash and GGBS and the numerical value indicates the percentage of replacement of cement by fly ash and GGBS).The cube specimens are taken of size 150 mm x 150 mm x 150 mm. Ambient curing of concrete at room temperature was adopted. In total 36 cubes were casted for different mix Id and the cube specimens are tested for their compressive strength at age of 1 day, 7 days and 28 days respectively. It was observed that the mix Id F60G40 gave maximum compressive strength of 80.50 N/mm2 at 28days.
2) Raijiwala D.B. & Patil H. S.(2011).This paper presents the progress of the research on making Geopolymer concrete using the Thermal Power Plant fly ash, (Ukai) Gujarat, India. The project aims at making and studying the different properties of Geopolymer concrete using this fly ash and the other ingredients locally available in Gujarat. Potassium Hydroxide and sodium Hydroxide solution were used as alkali activators in different mix proportions. They compared M25 mix OPC concrete with different proportions of geoploymer concrete with varying molarity of the activators by conducting different laboratory experiments. The results show that Compressive strength of GPC increases over conventional concrete by 1.5 times, Split Tensile Strength of GPC increases over conventional concrete by 1.45 times. Flexural Strength of GPC increases over conventional concrete by 1.6 times.
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4.0 GEO-POLYMER CONCRETE The term ‘geopolymer’ was first introduced by Davidovits in 1978 to describe a family of mineral binders with chemical composition similar to zeolites but with an amorphous microstructure. Geopolymerization involves the chemical reaction of alumino-silicate oxides (Si2O5,Al2O2) with alkali polysilicates yielding polymeric Si – O – Al bonds.
Fig.1.1 Chemical structure of polysialates
Unlike ordinary Portland/pozzolanic cements, geopolymers do not form calcium silicate-hydrates (CSHs) for matrix formation and strength, but utilise the polycondensation of silica and alumina precursors and a high alkali content to attain structural strength.
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Fig.1.2 Polycondensation by alkali into polysialates.
Therefore, geopolymers are sometimes referred to as alkali activated alumino silicate binders. However, Davidovits (1999; 2005) stated that using the term ‘alkali-activated’ could create significant confusion and generate false granted ideas about geopolymer concrete. For example, the use of the term ‘alkali-activated cement’ or ‘alkali-activated fly ash’ can be confused with the term ‘Alkali-aggregate reaction (AAR)’ , a harmful property well known in concrete.
4.1 SOURCE MATERIALS AND ALKALINE LIQUIDS There are two main constituents of geopolymers, namely the source materials and the alkaline liquids. The source materials for geopolymers based on alumino-silicate should be rich in silicon (Si) and aluminium (Al). These could be natural minerals such as kaolinite, clays, micas, andalousite, spinel, etc whose empirical formula contains Si, Al, and oxygen (O). Alternatively, by-product materials such as fly ash, silica fume, slag, rice-husk ash, red mud, etc could be used as source materials. The choice of the source materials for making geopolymers depends on factors such as availability, cost, and type of application and specific demand of the end users. The alkaline liquids are from soluble alkali metals that are usually Sodium or Potassium based. Low-calcium (ASTM Class F) fly ash is preferred as a source material than high-calcium (ASTM Class C) fly ash. The presence of calcium in high amounts may interfere with the polymerization process and alter the microstructure.
4.2 CONSTITUENTS OF GEO-POLYMER CONCRETE The materials used for making fly ash-based geopolymer concrete specimens are low-calcium dry fly ash as the source material, aggregates, alkaline liquids, water, and admixtures. 4.2.1 Fly ash Geo-polymer concrete can be manufactured by using the low-calcium (ASTM Class F) fly ash obtained from coal-burning power stations. Most of the fly ash available globally is low-calcium fly ash formed as a by-product of burning anthracite or bituminous coal. Although coal burning power plants are considered to be environmentally unfriendly, the extent of power generated by these plants is on the increase due to the huge reserves of good quality coal available worldwide and the low cost of power produced from these sources. 5
Low-calcium fly ash has been successfully used to manufacture geo-polymer concrete when the silicon and aluminum oxides constituted about 80% by mass, with the Si-to-Al ratio of about 2. The content of the iron oxide usually ranged from 10 to 20% by mass, whereas the calcium oxide content is less than 5% by mass. The carbon content of the fly ash, as indicated by the loss on ignition by mass, is as low as less than 2%.
Fig.1.3 Low calcium fly ash
Fig.1.4 Blast furnace slag
4.2.2 Aggregates Local aggregates, comprising of 20 mm nominal size coarse aggregates and fine aggregates, in saturated surface dry condition, should be used. The coarse aggregates were crushed granite-type aggregates which is to be free from impurities and Sand as fine aggregate should be free from silt content. Both aggregates should be conforming to IS standards 383-1970. 4.2.3 Alkaline Liquid The alkaline liquid should be a combination of sodium silicate solution and sodium hydroxide solution. It is recommended that the alkaline liquid is prepared by mixing both the solutions together at least 24 hours prior to use. The sodium hydroxide with 97-98% purity, in flake or pellet form, is commercially available. In order to improve the workability, a high range water reducer super plasticizer and extra water may be added to the mixture
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4.3 MIXTURE PROPORTIONS OF GEOPOLYMER CONCRETE The primary difference between geopolymer concrete and Portland cement concrete is the binder. The silicon and aluminum oxides in the low-calcium fly ash reacts with the alkaline liquid to form the geopolymer paste that binds the loose coarse aggregates, fine aggregates, and other un-reacted materials together to form the geopolymer concrete. As in the case of Portland cement concrete, the coarse and fine aggregates occupy about 75 to 80% of the mass of geopolymer concrete. This component of geopolymer concrete mixtures can be designed using the tools currently available for Portland cement concrete. The compressive strength and the workability of geopolymer concrete are influenced by the proportions and properties of the constituent materials that make the geopolymer paste. The parameters on the compressive strength and the workability of geopolymer concrete is complex. In order to assist the design of low-calcium fly ash-based geopolymer concrete mixtures, a single parameter called 'water-to-geopolymer solids ratio' by mass was devised. In this parameter, the total mass of water is the sum of the mass of water contained in the sodium silicate solution, the mass of water in the sodium hydroxide solution, and the mass of extra water, if any, added to the mixture. The mass of geopolymer solids is the sum of the mass of fly ash, the mass of sodium hydroxide solids, and the mass of solids in the sodium silicate solution (i.e. the mass of Na2O and SiO2).
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4.4 MIXING OF GPC Geopolymer concrete can be manufactured by adopting the conventional techniques used in the manufacture of Portland cement concrete. Mixing can be done manually or by Machine mixing. Below machine mixing of the ingredients is shown. The fly ash and the aggregates are first mixed together dry in 80-litre capacity pan mixer (see figure below) for about three minutes.
Fig.1.5 M/c Mixing of GPC
Fig.1.6 Hand mixing of GPC The fresh concrete could be handled up to 120 minutes without any sign of setting and without any degradation in the compressive strength. 8
The fresh concrete can cast and compacted by the usual methods used in the case of Portland cement concrete.
4.5 CURING OF GPC Heat-curing of low-calcium fly ash-based geopolymer concrete is generally recommended. Heatcuring substantially assists the chemical reaction that occurs in the geopolymer paste. Both curing time and curing temperature influence the compressive strength of geopolymer concrete. Longer curing time improved the polymerization process resulting in higher compressive strength. The rate of increase in strength is rapid up to 24 hours of curing time; beyond 24 hours, the gain in strength is only moderate. Therefore, heat-curing time need not be more than 24 hours in practical applications. Heat-curing can be achieved by either steam-curing or dry-curing. Test data show that the compressive strength of dry-cured geopolymer concrete is approximately 15% larger than that of steam-cured geopolymer concrete .The temperature required for heat-curing can be as low as 30°C. A two-stage steam-curing regime was also used in the manufacture of prototype reinforced geopolymer concrete box culverts. It was found that steam curing at 80°C for a period of 4 hours provided enough strength for de-moulding of the culverts; this was then followed by steam curing further for another 20 hours at 80°C to attain the required design compressive strength. Also, the start of heat-curing of geopolymer concrete can be delayed for several days. Tests have shown that a delay in the start of heat-curing up to five days did not produce any degradation in the compressive strength. Infact, such a delay in the start of heat-curing substantially increased the compressive strength of geopolymer concrete. This may be due to the geopolymerisation that occurs prior to the start of heat-curing.
Fig.1.7 Oven curing
Fig.1.8 Steam curing
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4.6 PROPERTIES OF GEOPLOYMER CONCRETE Geopolymers possess high early strength, low shrinkage, sulfate resistance, corrosion resistance, acid resistance, fire resistance, and no dangerous alkali-aggregate reaction. Based on laboratory tests, Davidovits (1988b) reported that geopolymer cement can harden rapidly at room temperature and gain the compressive strength in the range of 20 MPa after only 4 hours at 20oC and about 70100 MPa after 28 days. Comrie et. al., (1988) conducted tests on geopolymer mortars and reported that most of the 28- day strength was gained during the first 2 days of curing. Geopolymeric cement was superior to Portland cement in terms of heat and fire resistance, as the Portland cement experienced a rapid deterioration in compressive strength at 300oC, whereas the geopolymeric cements were stable up to 600Oc (Davidovits, 1988b; 1994b). It has also been shown that compared to Portland cement, geopolymeric cement has extremely low shrinkage. The presence of alkalis in the normal Portland cement or concrete could generate dangerous AlkaliAggregate-Reaction. However the geopolymeric system is safe from that phenomenon even with higher alkali content. As demonstrated by Davidovits (1994a; 1994b), based on ASTM C227 bar expansion test, geopolymer cements with much higher alkali content compared to Portland cement did not generate any dangerous alkali-aggregate reaction where the Portland cement did. Geopolymer cement is also acid-resistant, because unlike the Portland cement, geopolymer cements do not rely on lime and are not dissolved by acidic solutions. As shown by the tests of exposing the specimens in 5% of sulfuric acid and chloric acid, geopolymer cements were relatively stable with the weight lose in the range of 5-8% while the Portland based cements were destroyed and the calcium alumina cement lost weight about 30-60% (Davidovits, 1994b). Geopolymers or geopolymer concrete is superior to Portland cement concrete in terms of acid resistance as the weight loss is much lower.
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4.7 ADVANTAGES AND DIS-ADVANTAGES OF GPC 4.7.1 ADVANTAGES: 1. High Strength – It has a high compressive strength that showed higher compressive strength than that of ordinary concrete. It also has rapid strength gain and cures very quickly, making it an excellent option for quick builds. Geopolymer concrete has high tensile strength. It is less brittle than Portland concrete and can withstand more movement. It is not completely earthquake proof, but does withstand the earth moving better than traditional concrete. 2. Very Low Creep and Shrinkage – shrinkage can cause severe and even dangerous cracks in the concrete from the drying and heating of the concrete or even the evaporation of water from the concrete. Geopolymer concrete does not hydrate; it is not as permeable and will not experience significant shrinkage. The creep of geopolymer concrete is very low. When speaking of creep in concrete terms it means the tendency of the concrete to become permanently deformed due to the constant forces being applied against it. 3. Resistant to Heat and Cold – It has the ability to stay stable even at temperatures of more than 2200 degrees Fahrenheit. Excessive heat can reduce the stability of concrete causing it to spall or have layers break off. Geopolymer concrete does not experience spalling unless it reaches over 2200 degrees Fahrenheit. As for cold temperatures, it is resistant to freezing. The pores are very small but water can still enter cured concrete. When temperatures dip to below freezing that water freezes and then expands this will cause cracks to form. Geopolymer concrete will not freeze. 4. Chemical Resistance – it has a very strong chemical resistance. Acids, toxic waste and salt water will not have more effect on geopolymer concrete. 5. Environmental Benefits- The use of geopolymer concrete reduces the need of OPC, which helps to reduce the environmental pollution that caused by the emission of CO2 during the production of OPC.
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4.7.2 DIS-ADVANTAGES 1. Difficult To Create Geopolymer concrete requires special handling needs and is extremely difficult to create. It requires the use of chemicals, such as sodium hydroxide, that can be harmful to humans which causes irritation and permanently damages tissue which come in contact with. 2. Geopolymerization Process Is Sensitive This field of study has been proven inconclusive and extremely volatile. Uniformity is lacking. 3. Development of strengths and other keys properties of GPC are directly dependent on the purity of the resource materials. Maintaining homogeneity in the source materials such as fly ash etc and purity of alkaline materials obtained from different manufacturers for preparing activator solutions make the design of this concrete mix proportions difficult for its manufacture on a recipe. 4. High alkalinity environment possess health hazards to the workers. Higher alkalinity of the materials requires more processing resulting in more energy consumption and hence generation of greenhouse gases. 5. Production of GPC requires great care in contrast to portland cement concrete.
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4.8 APPLICATIONS OF GPC According to Davidovits (1988), geopolymeric materials have a wide range of applications in the field of industries such as in the automobile and aerospace, nonferrous foundries and metallurgy, civil engineering and plastic industries. The type of application of geopolymeric materials is determined by the chemical structure in terms of the atomic ratio Si:Al in the polysialate. Davidovits (1999) classified the type of application according to the Si:Al ratio as presented in Table below . A low ratio of Si:Al of 1, 2, or 3 initiates a 3DNetwork that is very rigid, while Si:Al ratio higher than 15 provides a polymeric character to the geopolymeric material. Table-1. Applications of GPC
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4.9 CONCLUSIONS Geopolymer concrete is well known for its promising mechanical properties, acid resistance and fire resistance and therefore is a potential alternative construction material with comparable properties to OPC concrete. The constituents of Geopolymer Concrete shall be capable of being mixed with a relatively low alkali activating solution and must be curable in a reasonable time under ambient conditions. Geopolymers emit approximately 80% less CO2 than OPC during production, making it a more environmental friendly building material. Like OPC concrete, geopolymer concrete has a brittle failure. Alternatively, fibres can be added to improve the ductility of concrete. The properties of geopolymer include high early strength, low shrinkage, freeze-thaw resistance, sulphate resistance and corrosion resistance. These high-alkali binders do not generate any alkali-aggregate reaction. The geopolymer binder is a low CO2 cementious material. It does not depend on the Calcination of limestone that generates CO2. This technology can save up to 80% of CO2 emissions caused by the cement and aggregate industries. Due to the high early strength, Geopolymer Concrete shall be effectively used in the precast industries, so that huge production is possible in short duration of time.
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5.0 REFERENCES 1.0 L.Krishnan, S.Karthikeyan, S.Nathiya and K. Suganya on “Geopolymer Concrete an Ecofriendly Construction Material” [International Journal of Research in Engineering and Technology (2014), pages-164-167]. 2.0 Raijiwala D.B. and Patil H. S. on “Geopolymer Concrete: A Concrete of Next Decade” [Journal of Engineering Research and Studies (2011), pages-19-25]. 3.0 Mohd Mustafa Al Bakri, H. Mohammed, H. Kamarudin, I. Khairul Niza and Y. Zarina on “Review on fly ash-based geopolymer concrete without Portland Cement”[ Journal of Engineering and Technology Research (2011) Vol. 3(1), pp. 1-4] 4.0 Wallah SE on “Drying Shrinkage of Heat-Cured Fly Ash-Based Geopolymer Concrete.” [Modern Appl. Sci., (2009) 3: 12.]
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