Academic literature on the topic 'Geopolymer concrete'

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, May, 2020<br>Cataloged from the official PDF of thesis.<br>Includes bibliographical references (page 36).<br>Geopolymers are inorganic polymers based on aluminosilicates that are produced from synthesizing pozzolanic compounds or aluminosilicate source materials with highly alkaline solutions. Geopolymer concrete is a stronger, more durable and more environmentally friendly alternative to ordinary Portland cement (OPC) concrete. Based on Joseph Davidovits' recipe for geopolymer concrete, we varied the ratios of the materials in an attempt to produce the ideal formula for the concrete that withstands maximum compressive strength. Through our iterations, we found the optimum texture was produced when the amount of sodium carbonate and lime are proportionally increased relative to the rest of the materials.<br>by Xin Yin Lo.<br>M. Eng.<br>M.Eng. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Coal powered power plants account for more than 40 percent of the electricity production of the United States. The combustion of coal results in a large number of solid waste materials, or coal combustion byproducts (CCBs). These waste materials are stored in landfill or ponds. The construction industry is heavily reliant on concrete which is used to make the building blocks for any type of structures, bricks. Concrete is a composite material made of a binder and coarse and fine aggregate. The most widely used binder in concrete production is Ordinary Portland Cement (OPC). Since cement manufacture is costly and environmentally damaging, research has increased in recent years to find a more readily available binder. This study aims at investigating the properties of Illinois fly ash as a binder in the production of geopolymer concrete. Geopolymer concrete is an innovative material made by using Alumina and Silica rich materials of geological origins as a binder as well as an alkali activated solution. Sodium Silicate and Sodium Hydroxide were used to make the activator solution of two different ratios. Geopolymer Concrete with a ratio of 1:1 of Sodium Silicate to Sodium Hydroxide reached a compressive strength above 6000 psi while samples made with a ratio of 1:2 reached a compressive strength above 4000 psi. This environmentally-friendly, green concrete was also found to have a cost comparable to conventional concrete.

The use of Portland cement in concrete construction is under critical review due to high amount of carbon dioxide gas released to the atmosphere during the production of cement. In recent years, attempts to increase the utilization of fly ash to partially replace the use of Portland cement in concrete are gathering momentum. Most of this by-product material is currently dumped in landfills, creating a threat to the environment. Geopolymer concrete is a ‘new’ material that does not need the presence of Portland cement as a binder. Instead, the source of materials such as fly ash, that are rich in Silicon (Si) and Aluminium (Al), are activated by alkaline liquids to produce the binder. Hence concrete with no Portland cement. This thesis reports the details of development of the process of making fly ash-based geopolymer concrete. Due to the lack of knowledge and know-how of making of fly ashbased geopolymer concrete in the published literature, this study adopted a rigorous trial and error process to develop the technology of making, and to identify the salient parameters affecting the properties of fresh and hardened concrete. As far as possible, the technology that is currently in use to manufacture and testing of ordinary Portland cement concrete were used. Fly ash was chosen as the basic material to be activated by the geopolimerization process to be the concrete binder, to totally replace the use of Portland cement. The binder is the only difference to the ordinary Portland cement concrete. To activate the Silicon and Aluminium content in fly ash, a combination of sodium hydroxide solution and sodium silicate solution was used. Manufacturing process comprising material preparation, mixing, placing, compaction and curing is reported in the thesis.Napthalene-based superplasticiser was found to be ii useful to improve the workability of fresh fly ash-based geopolymer concrete, as well as the addition of extra water. The main parameters affecting the compressive strength of hardened fly ash-based geopolymer concrete are the curing temperature and curing time, the molar H2O-to-Na2O ratio, and mixing time. Fresh fly ash-based geopolymer concrete has been able to remain workable up to at least 120 minutes without any sign of setting and without any degradation in the compressive strength. Providing a rest period for fresh concrete after casting before the start of curing up to five days increased the compressive strength of hardened concrete. The elastic properties of hardened fly ash-based geopolymer concrete, i,e. the modulus of elasticity, the Poisson’s ratio, and the indirect tensile strength, are similar to those of ordinary Portland cement concrete. The stress-strain relations of fly ash-based geopolymer concrete fit well with the expression developed for ordinary Portland cement concrete.

The use of Portland cement in concrete construction is under critical review due to high amount of carbon dioxide gas released to the atmosphere during the production of cement. In recent years, attempts to increase the utilization of fly ash to partially replace the use of Portland cement in concrete are gathering momentum. Most of this by-product material is currently dumped in landfills, creating a threat to the environment. Geopolymer concrete is a ‘new’ material that does not need the presence of Portland cement as a binder. Instead, the source of materials such as fly ash, that are rich in Silicon (Si) and Aluminium (Al), are activated by alkaline liquids to produce the binder. Hence concrete with no Portland cement. This thesis reports the details of development of the process of making fly ash-based geopolymer concrete. Due to the lack of knowledge and know-how of making of fly ashbased geopolymer concrete in the published literature, this study adopted a rigorous trial and error process to develop the technology of making, and to identify the salient parameters affecting the properties of fresh and hardened concrete. As far as possible, the technology that is currently in use to manufacture and testing of ordinary Portland cement concrete were used. Fly ash was chosen as the basic material to be activated by the geopolimerization process to be the concrete binder, to totally replace the use of Portland cement. The binder is the only difference to the ordinary Portland cement concrete. To activate the Silicon and Aluminium content in fly ash, a combination of sodium hydroxide solution and sodium silicate solution was used. Manufacturing process comprising material preparation, mixing, placing, compaction and curing is reported in the thesis.<br>Napthalene-based superplasticiser was found to be ii useful to improve the workability of fresh fly ash-based geopolymer concrete, as well as the addition of extra water. The main parameters affecting the compressive strength of hardened fly ash-based geopolymer concrete are the curing temperature and curing time, the molar H2O-to-Na2O ratio, and mixing time. Fresh fly ash-based geopolymer concrete has been able to remain workable up to at least 120 minutes without any sign of setting and without any degradation in the compressive strength. Providing a rest period for fresh concrete after casting before the start of curing up to five days increased the compressive strength of hardened concrete. The elastic properties of hardened fly ash-based geopolymer concrete, i,e. the modulus of elasticity, the Poisson’s ratio, and the indirect tensile strength, are similar to those of ordinary Portland cement concrete. The stress-strain relations of fly ash-based geopolymer concrete fit well with the expression developed for ordinary Portland cement concrete.

Inclusion of ground granulated blast furnace slag (GGBFS) together with fly-ash can have significant effects on the development of mechanical and durability properties of geopolymer concrete when cured at normal temperature. The slag blended geopolymer concretes showed durability properties comparable to those of the control OPC concrete. In general, the results show that it is possible to design fly ash and slag blended geopolymer concrete suitable for ambient curing with similar or better durability properties of conventional OPC concrete.

Production of ordinary Portland cement (OPC) is a carbon-intensive process that generates significant amounts of carbon dioxide (CO2) gas from the combustion of fossil fuels and thermal decomposition of limestone. Overall, cement industries are responsible for around 7% of global CO2 emissions which poses a considerable threat to global climate change because of its greenhouse effects. Geopolymer is an inorganic polymer material having similar binding properties to OPC which can be produced from aluminosilicate compounds, such as fly ash when activated by alkaline solution. The recent advent of geopolymer technology shows great potential to reduce carbon footprints by utilising industrial by-products, such as fly ash and ground granulated blast furnace slag (GGBS), and convert into effective binding material. The setting and hardening process of geopolymer binder is different from hydration of OPC, called “geopolymerisation” which is the condensation process of aluminate and silicate monomers to form a polymer chain. Generally, fly ash-based geopolymer concrete attains relatively lower early-age strength at ambient temperature due to the slow rate of reaction. However, geopolymer concrete based on GGBS or a combination of fly ash and GGBS can set and harden in ambient temperature with comparable early age strength to OPC concrete of same grade. In the recent past, several studies were carried out to investigate mechanical, serviceability, durability and microstructural properties of geopolymer concrete using different aluminosilicate materials. However, limited research has been carried out on applications of geopolymer binder in structural concrete, such as reinforced concrete beam, column and prestressed concrete beam. Prestressed concrete is a construction technique in which flexural tensile stress generated in the concrete member due to imposed load is counteracted by applying an initial prestressing compressive force. The use of prestressed concrete structures has been increasing in modern construction practices because they can withstand significantly higher flexural load with minimal deflection and cracks than conventional reinforced concrete (RC) members of similar cross-section. Generally, tensile strength of concrete is ignored in the design of conventional RC structures. However, tensile or flexural strengths of concrete are significant in the design of prestressed concrete structures where tensile strength of concrete limits the maximum permissible prestressing load according to ACI 318. Application of higher prestressing load can increase the load-carrying capacity of prestressed concrete structures and minimize their deflection under service load. Previous results showed that geopolymer concrete possesses higher indirect-tensile and flexural strength than OPC concrete for the same compressive strength. In addition, time-dependent losses of prestressing stress are the major serviceability problems of prestressed concrete structure which reduce the load-carrying capacity of structures and increase the deflection under service loads. The time-dependent losses of prestressing stress are directly proportional to the amount of shrinkage and creep strains of concrete. Having smaller drying shrinkage and creep strains, geopolymer concrete can result in better serviceability than OPC concrete in prestressed concrete structures. Thus, this study investigates the application of geopolymer concrete in the prestressed concrete beam which may be a worthwhile utilization of geopolymer concrete in concrete structures. Despite having higher mechanical strengths and durability properties than conventional OPC concrete, geopolymer concrete has not been widely used in structural grade concrete, so far. The safety hazards in mixing and handling of concrete due to the use of liquid sodium hydroxide in geopolymer binder is one of the barriers to the adaptation of geopolymer in concrete industry. In this study, the mechanical and serviceability properties of grade 50 MPa geopolymer concrete from sodium hydroxide-free one-part geopolymer binder are investigated under ambient temperature curing and compared against same grade OPC concrete. Development of strengths at an early age under accelerated curing is investigated to study the suitability of geopolymer concrete in precast prestressed concrete structures. Finite element models of prestressed concrete beams of three different lengths and sizes are analysed to investigate their load-deflection behaviours under imposed load for short-term and long-term durations using the Abaqus program. The effects of tensile strength of concrete in load-deflection behaviours of prestressed concrete beams are studied by comparing the results between identical geopolymer and OPC prestressed concrete beams. This study finds that geopolymer concrete has around 27% higher indirect-tensile and flexural strengths than OPC concrete of same strength grade which contributes to geopolymer prestressed concrete beams to withstand around 20% higher first-crack load than OPC concrete beams of same span. In addition, geopolymer prestressed concrete beams show a relatively smaller loss in prestressing stress which results in a smaller loss in flexural capacity of beams over the service life of the structure.

Concrete is by far the most widely used construction material worldwide in terms of volume, and so has a huge impact on the environment, with consequences for sustainable development. Portland cement is one of the most energy-intensive materials of construction, and is responsible for some emissions of carbon dioxide — the main greenhouse gas causing global warming. Efforts are being made in the construction industry to address these by utilising supplementary materials and developing alternative binders in concrete; the application of geopolymer technology is one such alternative. Indeed, geopolymers have emerged as novel engineering materials with considerable promise as binders in the manufacture of concrete. Apart from their known technical attributes, such as superior chemical and mechanical properties, geopolymers also have a smaller greenhouse footprint than Portland cement binders.Research on the development, manufacture, behaviour and applications of low calcium fly ash-based geopolymer concrete has been carried out at Curtin University of Technology since 2001. Past studies of the structural behaviour of reinforced fly ash-based geopolymer concrete members have covered the flexural behaviour of members. Further studies are needed to investigate other aspects of the structural behaviour of geopolymer concrete. Design for both shear and bond are important in reinforced concrete structures. Adequate shear resistance in reinforced concrete members is essential to prevent shear failures which are brittle in nature. The performance of reinforced concrete structures depends on sufficient bond between concrete and reinforcing steel. The present research therefore focuses on the shear and bond behaviour of reinforced low calcium fly ash-based geopolymer concrete beams.For the study of shear behaviour of geopolymer concrete beams, a total of nine beam specimens were cast. The beams were 200 mm x 300 mm in cross section with an effective length of 1680 mm. The longitudinal tensile reinforcement ratios were 1.74%, 2.32% and 3.14%. The behaviour of reinforced geopolymer concrete beams failing in shear, including the failure modes and crack patterns, were found to be similar to those observed in reinforced Portland cement concrete beams. Good correlation of test-to-prediction value was obtained using VecTor2 Program incorporating the Disturbed Stress Field Model proposed by Vecchio (2000). An average test-to-prediction ratio of 1.08 and a coefficient of variation of 8.3% were obtained using this model. It was also found that the methods of calculations, including code provisions, used in the case of reinforced Portland cement concrete beams are applicable for predicting the shear strength of reinforced geopolymer concrete beams.For the study of bond behaviour of geopolymer concrete beams, the experimental program included manufacturing and testing twelve tensile lap-spliced beam specimens. No transverse reinforcement was provided in the splice region. The beams were 200 mm wide, 300 mm deep and 2500 mm long. The effect of concrete cover, bar diameter, splice length and concrete compressive strength on bond strength were studied. The failure mode and crack patterns observed for reinforced geopolymer concrete beams were similar to those reported in the literature for reinforced Portland cement beams. The bond strength of geopolymer concrete was observed to be closely related to the tensile strength of geopolymer concrete. Good correlation of test bond strength with predictions from the analytical model proposed by Canbay and Frosch (2005) were obtained when using the actual tensile strength of geopolymer concrete. The average ratio of test bond strength to predicted bond strength was 1.0 with a coefficient of variation of 15.21%. It was found that the design provision and analytical models used for predicting bond strength of lapsplices in reinforced Portland cement concrete are applicable to reinforced geopolymer concrete beams.

In order to adopt geopolymer concrete as a pavement repair material due to its better durability, splitting and slant shear tests are performed. Effect of curing time, degradation of the pavement concrete under different acid conditions on the bond strength of geopolymer with conventional concrete, and comparison of the metakaolin geopolymer with other pavement repair materials are analyzed. It was found curing time affects the interface bond strength greatly and the interface bond strength degrades quickly in an acid environment. Effect of molar ratio of SiO2/Na2O, calcium aluminate cement, and slag on early strength of the geopolymer have been studied. It was found molar ratio of SiO2/Na2O of 1.0 gave the highest early strength in 24 hours. Also, freeze-thaw durability of geopolymer concrete are investigated by exposing the specimens to rapid freeze-thaw cycles. Based on these research results, adopting metakaolin geopolymer in accelerated PCC pavement repairs is a feasible option.

AN ABSTRACT OF THE THESIS OF NAVIN PAIJA, for the Master of Science degree in CIVIL ENGINEERING, presented on 04/06/2017, at Southern Illinois University Carbondale. FEASIBILITY STUDY OF USING GROUND BOTTOM ASH IN GEOPOLYMER CONCRETE MAJOR PROFESSOR: Dr. Sanjeev Kumar Dr. Manoj K. Mohanty United States alone has about three quarters of the accessible worldwide reserve of coal. There are about 511 coal-powered electric plants and generates about 33% of the nation’s electricity. The combustion of coal results in a large number of solid waste materials known as coal combustion byproducts (CCBs) that are stored in landfill or ponds. These are easily accessible and with proper research it can be put into beneficial use. Today concrete is the second most consumed substance after water. Concrete, a composite material made of a binder in combination with coarse and fine aggregate, is used in foundations and structures of buildings, bridges, roads, dams. Cement is the most widely used binder for concrete, however, research has shown that a single cement industry produces approximately 5% of global CO2 emissions, and one ton of Portland cement emits approximately one ton of CO2. This emission of CO2 is one of the main reasons for global warming and has detrimental impacts on environment. The possibility of using fly ash and bottom ash as an alternative to cement as a binder to produce sustainable concrete is investigated in this study. The process of geopolymerization includes the reaction of ash and an alkali activated solution made of diluted sodium silicate and sodium hydroxide. The initial objective of this study was to produce fly ash geopolymer concrete which has a strength comparable to that of cement concrete. However, later the possibility of bottom ash as a binder material for geopolymer production was also studied. During this study, the strength of conventional mortar with 10%, 20%, and 30% cement replacement with fly ash and bottom ash was experimented and compared with strength of cement mortar. The test results showed that with increase in the fly ash and bottom ash replacement the strength of the mortars decreased, moreover, the mortars that was replaced by bottom ash produced better results than that of the fly ash replacement. Also, the effect of increase in the ratio of sodium silicate to sodium hydroxide ratio on the strength of geopolymer mortar is studied. Sodium silicate to sodium hydroxide ratio of 1.5, 2.5, and 3 is used in this ratio, and the test results showed that with the increase in this ratio the compressive strength of geopolymer mortar also increased. Similarly, different combinations of fly ash and bottom ash is used to produce geopolymer mortars. The results showed that geopolymer mortar with higher bottom ash content produced better results. The effect of ground fly ash and bottom ash on the compressive strength of geopolymer mortar is also studied. The test result showed that with increase in fineness of fly ash and bottom ash, there was slight improvement in the strength.

This thesis focuses on the behaviour of fly ash based geopolymer concrete columns under axial load and biaxial bending. Tests showed that failure load of columns increased with the increase of concrete compressive strength and longitudinal reinforcement ratio, and decreased with the increase of load eccentricity. Use of the Bresler’s reciprocal load formula with an iterative procedure for slender columns in uniaxial bending conservatively predicted the strength of the test columns.