DURABILITY OF STRUCTURE REPORT of GEOPOLYMER CONCRETE GREEN CONCRETE Tu T. Nguyen December 2009
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I. Introduction This subject points out a view of material behaviour, particularly behaviour of concrete. As well as fresh concrete technology has advanced at a pace similar to many other aspects of concrete technology over the past three decades, and indeed many these advances have been innerdependent. For example, the availability of super-plasticizer has enabled workable concrete to be produced at lower water/binder ratio thus increasing the strength.
In this paper, one report will be concerned with objective, principle and durability of structure with its potential in application. II. Specification With the increasing concern of the natural resources and environment, new technologies have been developed or are under developing in construct materials, particularly, in concrete.
This paper requires submitting a research report to give an overview on these technologies. An example of any one particular technology should be provided to find out advantage and disadvantage of objective, principles, what is the effect on durability and sustainability of structure with potential in application. application.
There is no limit on t he topics. For example, it could be high performance concrete for particular application, application, self compacting concrete, or the concrete used to abate CO2, etc.
III. Overview on application of advanced concrete technology Concrete is the world’s most important construction material. However, an abundance of raw material such as rock, gravel, sand and water in the concrete reaches approximately 75-90% produced annually in North European countries (Concrete for the environment, 2003). Therefore, the quality of concrete does not reach a necessary compressive strength. It is a reason for new technologies which should be discovered. discovered. At the same time, the world is tackling global warning and resources problem. New concrete technologies are an environmentally friendly material and are – when correctly produced and used very durable as a consequence. Structures at the ends of their lives can be demolished and recycled as aggregate in new concrete or for road construction. Hence, there are some of these advanced concrete technologies technologies to examine in this paper.
- Development of a Sustainable Concrete Waste Recycling System - Application of Recycled Aggregate Concrete Produced by Aggregate Replacing Method (Yasuhiro Dosho) ( Journal of Advanced Concrete Technology, Volume 5.1 (2007 ): ): In this paper, the research showed the reuse of construction waste is highly essential from the viewpoint of Life Cycle Assessment (LCA) and effective recycling of construction resources. Therefore, a promotion of the reuse of 2
construction waste is necessary to achieve three basic concepts: (1) assurance of safety and quality, (2) decrease of environmental impact, and (3) increase of cost effectiveness of construction. This paper outlines the development of a recycling system, application of recycled aggregate concrete produced by the aggregate replacing method, which is effective in reducing both cost and environmental impact from the viewpoint of LCA for concrete waste generated by the demolition of large-scale buildings. Result of this study showed that the adoption of the developed recycling system was confirmed to recycle concrete waste produced from the demolition buildings in a highly effective manner reducing both recycling cost and environmental impact.
- Geopolymer concrete technology (Dr. Erez Allouche) (Sciencedaily, 2009): This research is led by an assistant professor of civil engineering at Louisiana Tech University and associate director of the Trenchless Technology Center. In this paper, the research outlines a comparison between old concrete (Portland cement concrete (PCC)) and new concrete based Inorganic polymer concrete (geopolymer) in pumping carbon dioxide (CO 2) into our atmosphere. The research showed the geopolymer will contribute lower CO 2 than the PCC do. In addition, geopolymer concrete (GPC) features greater corrosion resistance, substantially higher fire resistance (up to 2400° F), high compressive and tensile strengths, a rapid strength gain, and lower shrinkage in comparison to ordinary Portland cement.
- Danish Experiences with a Decade of Green Concrete ( Claus Vestergaard Nielsen and Mette Glavind) (Journal of Advanced Concrete Technology, Volume 5.1 (2007) ): This research points
out a comparison of the Danish cement and concrete industry over last ten years. A reduction of Portland clinker content, which means improved amount of CO2 in the concrete, was involved in this area. Absorption of CO2 from the atmosphere was described in this 3-year project. It is the result of several scientific investigations for instance determining the effect of concrete emissions on the air quality and the solution to hydrocarbon pollution in concrete slurry at the concrete plant. Finally the article contains examples of how to improve the sustainability of concrete production and how to produce green concrete. Green concrete is the term used in Denmark for environmentally friendly concrete production and structu res.
- High strength concrete (Bill Price) (Newman (Newman J. and Choo B.S, B.S, 2003): The water/cement ratio is main cause for the strength of the paste. However, the paste’s strength depends on the porosity, because of the fragment size distribution of the crystalline phases and in-homogeneities within the hydrated paste.
Therefore, this technology outlines a new method will manufacture a newly mixture of concrete with higher strength by a reduction in water/cement ratio as a consequence of less capillary 3
porosity in the paste. A reduction of capillary porosity also supports the structure of fine-textured hydration products which have a higher strength than the previous concrete. In addition, the capillary porosity can be decreased by evaluating the particle size distribution of the cenemetitious cenemetitious materials in order to increase the potential packing density.
IV. Choice of research report Concrete and its constituent parts are available and used globally. It has been, is, and will continue to be the major construction material for mankind. As a consequence, we have a responsibility for concrete's effective design, construction and efficient use. Future resources, energy consumption, performance, durability, environmental and social impacts as well as economies are all importance ons which concrete’s sustainability will be evaluated - and this has a global significance. Increasingly, both political and practical levels, construction has to address and implement sustainability and towards this goal. However, Portland cement production, which is popular use in the global, is a major contributor to carbon dioxide (CO 2) emissions. It has pumped into the atmosphere about five to eight percent of all humangenerated atmospheric CO 2 worldwide. Production of Portland cement is currently toping 2.6 billion tons per year worldwide and growing at 5 percent annually (Erez Allouche, 2009).
In comparison to ordinary Portland cement (OPC), geo-polymer concrete (GPC) features greater corrosion resistance, substantially higher fire resistance (up to 2400° F), high compressive and tensile strengths, a rapid strength gain, and lower shrinkage. Perhaps Geopolymer concrete's greatest appeal is its life cycle greenhouse gas reduction potential; as much as 90% when compared with OPC (Erez Allouche, 2009).
In addition, as a considerable concern of the world when the world runs out resource and deals with global-warming, using concrete as a construction material actually helps us protect natural resources and offers consumers benefits that are not available with other building products such as steel or wood. In an area of increased attention to the environmental impact of construction and sustainable development, development, concrete has much to offer. Therefore, in this paper, geo-polymer concrete or “Green concrete” as an advanced concrete technology is reported to estimate positive and negative effect of this technology on environment and resources. The new technology is being concerned by human-being in the future, with objective and principle to provide the effects on durability and sustainability sustainability of structure with its potential in application.
Geo-polymer concrete has additionally the potential for basically reducing CO2 emissions, producing a more durable infrastructure capable of design life. It has a long life circle in comparison with Portland cement concrete about hundreds of years instead of tens (Erez
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Allouche, 2009). Particularly, it can self-protect aquifers and surface bodies of fresh water via the elimination of fly ash disposal sites.
V. Characteristic of Geoplymer concrete V.1 Principle The term “geopolymer” was invented by Davidovits in 1978. This inorganic aluminosilicate polymer is synthesized from predominantly silicon and aluminium material of geological origin or by-product materials such as fly ash, chemicial composition of geopolymer materials are similar to Zeolite. (R.Malathy (n.d.)).
Environmentally driven geopolymer applications are based on the implementation of (K,Ca)Poly(sialate-siloxo) / (K,Ca)-Poly(sialate-disiloxo) cements. In industrialized countries (Western countries) emphasis is put on toxic waste (heavy metals) and radioactive waste safe containment. On the opposite, in emerging countries, the applications relate to sustainable development, essentially geopolymeric cements with very low CO 2 emission. Both fields of application are strongly dependent on politically driven decisions.
V.2 The chemical composition The first chemical element in the geo-polymer geo-polymer founded in 1970 is the aluminosilicate kaolinite reacts with NaOH at 100°C-150°C and polycondenses into hydrated sodalite (a tecto-aluminosilicate), or hydro-sodalite hydro-sodalite (Davidovits, 2002): Si2O5,Al2(OH)4 Si2O5,Al2(OH)4 + NaOH ⇒ Na(-Si-O-Al-O)n kaolinite
hydrosodalite
The polymerisation process involves a substantially fast chemical reaction under alkaline condition on Si-Al minerals, those results in a three dimensional polymeric chain and ring structure consisting of -Si-O-Al-O- bonds, as follows: Mn [-(SiO2) z –AlO2] n.wH2O Since n is the degree of poly-condensation, M is predominantly a monovalent cation (K+, Na+), althought Ca2+ may replace two monovalent cations in the structure (Davidovits J., 1999). In the same result, Davidovits pointed out that although the SiO 2/Al2O3 ratio given by z is 1, 2 or 3 for the sialate-siloxo and sialate-disloxo-chains, even z can be higher than 3 (up to 32). This can be exaplained by cross linking of poly-silicate chains with a silicate link (-Si-O-Al-O-) bonds (Figure 2). Therefore, the geo-polymer material diagram can be shown as described by equations below (Edward G. Nawy, 2008):
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Figure 1 – Geo-polymer backbone and geo-polymer precursor Edward shows the formation of geo-polymer materials is shown in the first equation in figure 1, it is not clear since setting and hardening of geo-polymer precursor. Therefore, in terms of the second equation (geo-polymer backbone) shown in figure 1, water is released during the chemical bonds. The water removed from the geo-polymer matrix during the curvature. This is completely different from Portland cement concrete mixture during the hydration process. Hence, there are 2 main constituents of geo-polymer which are the source materials and the alkaline liquids. The most common alkaline liquid used in geo-polymerisation is a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate or potassium silicate.
Figure 2 Geo-polymer molecular networks V.3 Material Materials includes fly-ash (FA), sand Aggregates (SA), alkaline liquid (AL), water (W), superplasticizer (SP). In the batches of fly ash, the molar Si-to-Al ratio was about 1-3. A combination of sodium silicate solution and sodium hydroxide solution was chosen as the alkaline liquid. The sodium hydroxide (NaOH) solution was prepared by dissolving either the flakes or the pellets in water. The mass of NaOH solids in a solution varied depending on the concentration of the solution expressed in terms of molar, M. sand is small Aggregates in geo-polymer mortar. To improve the workability of the fresh geo-polymer mortar, super-plasticizer was used in most of the mixtures (Nguyen and Bui and Dang, 2008). 6
Figure 3: The beginning of the geo-polymers geo-polymers phase development on the surface of the fly ash particle V.4 Setting time of geo-polymer mortar Types of fly ash, composition of alkaline liquid and ratio of alkaline liquid to fly ash by mass are the factor during setting time of geo-polymer mortar. However the most important factor is the curing temperature. The figure below shows curing temperature has a significant effect on a similarity of setting time between initial setting-time and final setting-time.
Figure 4 Effect of curing temperature on setting time (Nguyen and Bui and Dang, Recent Research Geo-polymer Concrete, Concrete , 2008)
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Figure 5: Room temperature setting for concrete made of geo-polymer cements and Portland cements. (Geo-polyme (Geo-polymer: r: Inorganic Polymeric New Materials, Journal of Thermal Analysis, Vol 37, Davidovits, 1991) V.5. Compressive strength
As a highly above, GEO-polymer concrete has a major difference from Portland cement concrete is the binder (Edward G. Nawy, 2008). The silicon and aluminium oxides in the lowcalcium fly ash react with the alkaline liquid to form the geo-polymer paste that binds the loose coarse aggregates, fine aggregates and other did not react materials together to form the geopolymer concrete. As in case of Portland cement concrete, the coarse and fine aggregates occupy about 75% to 80% of the mass of geo-polymer geo-polymer concrete.
Figure 6: Fly ash before reacting with alkaline liquid
Figure 7: Fly ash after reacting with alkaline liquid
Therefore, the compressive strength and workability of geo-polymer concrete are influenced by the proportions and properties of the constituents that make the geo-polymer paste. Experiment results (Hardjito and Rangan, 2005)
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In terms of molar molar a higher concentration concentration of the sodium hydroxide sodium results results in the higher compressive strength of geo-polymer geo-polymer concrete.
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The higher higher ratio of of sodium sodium silicate silicate solution solution to sodium sodium hydroxide hydroxide solution by mass results in the higher compressive strength of geo-polymer concrete.
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The addition addition of naphthalene-su naphthalene-sulfonate-based lfonate-based super-plasticizers, super-plasticizers, up to 4% of fly ash by mass, improves the workability of fresh geo-polymer concrete. However, there is a slight degradation in the higher compressive strength of geo-polymer concrete of harden concrete when the super-plasticizers dosage is greater than 2%.
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The slump slump value value of the fresh geo-polymer geo-polymer concrete increases when the water water content content of the mixture increases.
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The H2O/Na2O molar ratio increases, the compressive compressive strength of geo-polymer concrete concrete decreases.
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The effect of the Na2O/Si2O molar ratio on the compressive strength of geo-polymer concrete is insignificant. insignificant.
Figure 8: Effect of water-to-polymer solids ratio by mass on compressive of geo-polymer geo-polymer concrete. (Hardjito, D. and Rangan, B. V. Development and Properties of Low-Calcium Fly Ash-based Geopolymer Concrete , Research Report GC1, Faculty of Engineering, Engineering, Curtin University of Technology, Perth, 2005) As can be seen from the above, compressive strength depends on curing time and curing temperature. As the curing time and curing temperature increase, the compressive strength increases. Curing temperature in (600C- 900C), curing time in (24h-72h), compressive strength 400-500 kG/cm2 as shown in figures below.
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Figure 9 - Extra water effects
Figure 10 - Effect of curing temperature
Figure 11 - Curing time effect
Figure 12 Effects of saturated water specimens
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V.6 Corrosion resistance The corrosion resistance of geo-polymer concrete is similar to this property of geo-polymer cement. Geo-polymer concreted has been excellent properties within both acid and salt environments environments since limestone has not used as a material in concrete. It is especially suitable for tough environmental conditions. The geo-polymer concrete can be become bend when it is in sea water environment. This can be useful in marine environments and on islands short of fresh water; in contrast Portland cement concrete is impossible in sea water.
Two grades of AAFG concretes were prepared for this investigation. G54 represents a Geopolymer concrete synthesised at high temperature (12 hours at 70°C) whereas G71 was achieved at ambient. They were used in resistance of corrosion in Fly Ash based Geo-polymer concrete research by X. J. Song, M. Marosszeky, M. Brungs, R. Munn.
As can be seen in Figure 11, the binder in the normal PC55 concrete shows significant degradation the aggregate becoming exposed after only 4 weeks in 10% sulphuric acid. By contrast, Geo-polymer concrete cubes, G71 and G54, remained structurally intact in the same acidic environments after 56 days, though some very fine localised cracks were observed (X. J. Song, 2005)
Figure 13: Appearance of concrete specimens exposed in 10% sulphuric acid (Left: PC55 f or 28 days, right: AAFG for 56 days) (X. J. Song, M. Marosszeky, M. Brungs, R. Munn, 2005) The samples are indicated that AAFG concrete is durable in 10% sulphuric acid up to 56 days by Song. In case of Portland concrete, the hydration compounds were naturalised by sulphuric acid and dramatically the binder disintegrated.
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Figure 14 Mass change in 10% sulphuric acid (X. J. Song, M. Marosszeky, M. Brungs, R. Munn, 2005) The samples have a low mass loss (figure 12) of Geo-polymer concretes in this research. This view is similar to Davidovit (1990) and Rostami and Brendley (2003). The compressive strength was used in this research to evaluate the impact of acid attack on mechanical performance. Although the strength reduction (Figure 13) was significant within the first week of immersion, this trend then became stable with residual strength up to 33 ~ 42 MPa after 56 days acid exposure (X. J. Song, M. Marosszeky, M. Brungs, R. Munn, 2005).
Figure 15 Compressive strength change of AAFG concretes in 10% sulphuric acid In addition, there is very interesting to compare the acid resistance between G54 and G71. a significant difference has shown in the 28 days strength development in the research. As expected, G54 has higher compressive strength than G71 due to the effect of higher temperature curing. However, both of them have a very similar trend in resisting sulphuric acid attack, in terms of mass change (Figure 12), compressive strength reduction (Figure. 13).
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Therefore AAFG concretes are acid resistant regardless of curing conditions. It also seems that Geopolymer concretes have the potential to be used in the production of pre-cast sewer pipes (high temperature curing) as well as in the repair of corroded pipes. VI. Geo-polymer concretes and the Green-house Global-warming challenge According to the research of Davidovits in 1991, CO 2 emissions resulting from chemical reactions will continue to increase with industrial development. This is specifically the case for Portland cement manufacturing. Cement results from calcinations of limestone (calcium carbonate) and silico-alumnious silico-alumnious material according to the reaction: 5CaCO3 + 2SiO2 = (3CaO,SiO2)(2CaO,SiO2) + 5CO2
[1]
The production of 1 tons cement generates 0.55 tons of CO 2 and needs the burn of carbon-fuel into 0.42s of CO2. To simplify: 1T cement = 1T CO2. However, The production of 1 tone of Geopolymeric cement generates 0.180 tones of CO2, from combustion carbon-fuel, compared with 1.00 tones of CO2 for Portland cement. Geo-polymeric cement generates six times less CO2 during manufacture than Portland cement. This simply means that, in newly industrialising countries, six times more cement for infrastructure and building applications might be manufactured, for the same emission of green house gas CO2. (Davidovits J, 2002). Indeed, Geopolymeric cement only requires the calcinations at 800°C for two geological ingredients, Carbunculus and KANDOXI. High furnace slag is a by-product that no longer needs any subsequent treatment. In addition, it is the processing of the development carried out on inorganic alumino-silicate alumino-silicate polymers or geo-polymers (Davidovits, 1985), resulting from t he geopolymeric reaction: 2Si2O5.Al2O2 + K2(H3SiO4)2 + Ca(H3SiO4)2 = (K2O.CaO)(8SiO2.2Al2O3.nH2O
[2]
The equation [2] release less CO 2 emission than the first equation. Therefore, geo-polymer concrete is more “green” than Portland cement concrete.
VII. Advantages and disadvantages of Geopolymer concrete VII.1.Advantages Fristly, This is one of the primary advantages of geopolymers over traditional cements from an environmental perspective is largely associated with releasing much lower CO 2 emission than Portland cement. This is mainly due to the absence of the high-temperature calcinations step in geopolymer synthesis.
Secondly, Geo-polymer concrete offers several economic benefits over Portland cement concrete. The price of a ton of fly ash is only small fraction of the price of a ton of Portland cement; therefore, after allowing for the price of the alkaline liquids required making the geopolymer concrete, the price of fly-ash-based geo-polymer concrete is estimated to be about 10 to 30% of Portland cement cement concrete. Furthermore, Furthermore, the very little drying shrinkage, shrinkage, low creep, excellent resistance to sulphate attack, and good acid resistance offered by the heat-cured, low13
calcium, fly-ash-based geo-polymer concrete may yield additional economic benefits when it is used in infrastructure application.
The other factor is geopolymer concrete offers increase resource efficiency by producing concrete products with longer services lives.
Corrosion resistance and high strength of geo-polymer geo-polymer are other factors. Geo-polymer concrete still keeps high compressive strength after mass loss and resisting from acid attack.
VII.2 Disadvantages Disadvantages Regardless of all these positive attributes, geo-polymer concrete is finding it hard to enter the modern market today. A main reason is because large cement companies are basically scared that the profit margins go down and financial risk. Another reason, the cost of geo-polymer is major factor. It is more expensive than Portland cement about 60% per cubic meter. (Cement and Concrete Research, Pacheco, Torgal et al., p 93).
In the construction industries view, “green cement” has yet to establish itself as a viable, just recognised or proven technology (Cement and Concrete Reseach, vol 37, p1591, Duxson et al, 2007).
VIII. Conclusion Construction and concrete industry have been utilising a tremendous amount of resources and energy. Therefore, they have a responsibility responsibility to reduce environmental impacts in their activities. For the concrete industry to contribute to the sustainable development of mankind, it is necessary to promote technical development for further reduction of environmental impacts. To promote this, it will be necessary to introduce environmental design systems based on environmental environmental performance, develop environmental performance evaluation tools and construct systems for their actual application.
It is obvious that the concrete sector also has to consider the reduction of environmental impacts in their technologies towards the sustainable development of human beings. The new century of concrete technologies is beginning with geo-polymer concrete. It releases lower carbon dioxide than traditional concrete. Geo-polymer offers many advantages in durability of structure such as increase of corrosion resistance, high compressive strength. Geo-polymer also has a high economic effect in concrete market today. In future, national and global environmental laws in regards to C02 emissions should force the Portland cement and concreting companies to convert to use ‘green cement’.
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