Ash Based Geopolymer Concrete Research Articles

Circular production of recycled binder from fly ash-based geopolymer concrete

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder.

Effect of Glass Fibre on Slag-Fly Ash based Geopolymer Concrete

Geopolymer concrete is a high strength environment friendly construction material. However, less ductility and high brittleness are the major challenges of the geopolymer concrete. The addition of fibres in concrete impedes the fracture propagation and improves the overall mechanical properties of the concrete. This study investigates the fresh and the hardened properties of ambient cured plain and glass fibre reinforced slag-fly ash based geopolymer concrete (SFGC). All the mixes were prepared using an alkaline solution, composed of 14 molar sodium hydroxide (NaOH) solution, and liquid sodium silicate (Na2SiO3) with a modulus (SiO2/Na2O) ratio of 2.5. Alkali resistant glass fibres at the dosage of 1.5% by volume of the concrete were added to the mix to evaluate the workability, density, compressive strength and flexural strength of glass fibre reinforced slag-fly ash based geopolymer concrete (GF-SFGC). The experimental results indicated that the addition of glass fibres in SFGC mix reduced the workability and density of concrete. The average compressive strength of SFGC determined at 7, 28 and 56 days was decreased by approximately 2-4% by adding the glass fibres into the mix. However, the average 28-day flexural strength of GF-SFGC was about 24% higher than the plain SFGC mix. Overall, GF-SFGC specimens remained intact even after the failure as compared to SFGC specimens.

Evaluation of strength and durability properties of fly ash-based geopolymer concrete containing GGBS and dolomite

Evaluation of strength and durability properties of fly ash-based geopolymer concrete containing GGBS and dolomite

Hyper-tuning gene expression programming to develop interpretable prediction models for the strength of corncob ash-modified geopolymer concrete

Geopolymer concrete has been offered as an alternative to traditional concrete due to the environmental consequences of cement manufacture. It is also unable to make adjustments if the concrete's strength after casting does not meet the required strength. Because of this, it is highly beneficial to make strength predictions before pouring concrete. This study proposes applying the gene expression programming (GEP) method to forecast the mechanical strength of slag and corncob ash-based geopolymer concrete (SCA-GPC). The SHapley Additive exPlanations (SHAP) approach was used to identify the significance of parameters used for modeling. Best-fitted simulations and exceptional prediction performance were produced by the GEP (R2 = 0.96, MAE = 1.876 MPa, MAPE = 6.00%, RMSE = 2.417 MPa, and NSE = 0.954), (R2 = 0.94, MAE = 0.178 MPa, MAPE = 3.50%, RMSE = 0.236 MPa, and NSE = 0.942), and (R2 = 0.94, MAE = 0.126 MPa, MAPE = 3.60%, RMSE = 0.154 MPa, and NSE = 0.935) for compressive, flexural, and split tensile strengths models of SCA-GPC, respectively. Error and efficiency-based statistical checks confirmed the accuracy of the created models. The SHAP research also found that the mechanical strength of SCA-GPC was mostly controlled by slag quantity, curing age, water quantity, and fine aggregate quantity in the mix proportion. This research showed that the mechanical strength of SCA-GPC could be effectively predicted using the GEP method. The implementation of such methods will significantly improve the process of ensuring the quality of geopolymer concrete.

Behavior and Correlations between different Mechanical Properties of Fly Ash-based Geopolymer Concrete

Behavior and Correlations between different Mechanical Properties of Fly Ash-based Geopolymer Concrete

Effect on properties of geopolymer concrete by inclusion of recycled aggregate and methods to enhance the packing density of aggregate

Purpose This study aims to practically determine the optimum proportion of aggregates to attain the desired strength of geopolymer concrete (GPC) and then compare the results using established analytical particle packing methods. The investigation further aims to assess the influence of various amounts of recycled aggregate (RA) on properties of low-calcium fly ash-based GPC of grade M25. Design/methodology/approach Fine and coarse aggregates were blended in various proportions and the proportion yielding maximum packing density was selected as the optimum proportion and they were compared with analytical models, such as Modified Toufar Model (MTM) and J. D. Dewar Model. RAs for this study were produced in laboratory and they were used in various amounts, namely, 0%, 50% and 100%. 12M NaOH solution was mixed with Na2SiO3 in the ratio of 1:2. The curing of concrete was done at the temperatures of 60° and 90 °C for 24, 48 and 72h. Findings The experimentally obtained optimum proportion of coarse to fine aggregate was 60:40 for all amounts of RA. Meanwhile, MTM and Dewar Model resulted in coarse aggregate to fine aggregates as 40:60, 45:55, 55:45 and 55:45, 35:65, 60:40, respectively, for 0% 100% and 50% RAs. The compressive strength of GPC elevated with the increase in curing regime. In addition, the ultrasonic pulse velocity also displayed a similar trend as that of strength. Originality/value The GPC with 50% RAs may be considered for use, as it exhibited superior properties compared to GPC with 100% RAs and was comparable to GPC with natural aggregates. Furthermore, compressive strength is correlated with split tensile strength and ultrasonic pulse velocity.

Optimization of constituent proportions for compressive strength of sustainable geopolymer concrete: A statistical approach

Geopolymer concrete (GPC) is an environmentally friendly and sustainable concrete produced through the geopolymerization process, involving the combination of alumino silicate materials with alkaline solutions. It has unique advantage of being carbon-negative which helps reduce carbon dioxide levels in the atmosphere. One challenge with making GPC is the significant variation in compressive strength that arises from differences in constituent proportions, specimen ages, andcuring conditions. There is a need to optimize the GPC constituents to achieve the desired compressive strength. To address this issue, a comprehensive dataset comprising 1242 data points from existing literature on fly ash-based GPC (FA-based GPC) was compiled for the purpose of optimizing the constituent proportions of GPC using statistical analysis. Nine independent variables were selected to develop the predictive models for compressive strength using linear (LRA), multilinear (MRA), and non-linear (NRA) regression analyses. The models were assessed using scatter plots between experimental and predicted responses and adopting the performance criteria such as the statistical significance of the model unknowns, R2 values, root mean square error (RMSE), mean absolute error (MAE), and scatter index (SI). LRA revealed that the compressive strength of GPC is not dependent on any single independent variable. Therefore regression analysis with multiple independent variables was conducted. From MRA, ±15 % error for training dataset and (15–20) % error for validating dataset was estimated. The R2, RMSE, MAE, and SI values were found to be 0.8086, 6.11, 5.35, and 0.21. NRA predicted the compressive strength more efficiently because it provides the error ±10 % for both training and validating datasets with R2, RMSE, MAE, SI values of 0.8321, 5.46, 4.77, and 0.19. Further, curing temperature, specimen age, Na2SiO3/NaOH ratio, I/b ratio, and aggregate content were found as the most significant independent variables. The time and cost-effective design mix for FA based GPC can be prepared using the regression models presented in the current work.

Influence of chemical constituents of binder and activator in predicting compressive strength of fly ash-based geopolymer concrete using firefly-optimized hybrid ensemble machine learning model

This study focuses on investigating the impact of chemical constituents in binders and activators on the prediction of strength, particularly proposing a novel hybrid ensemble model that synergizes the strengths of three base models optimized using the Firefly Algorithm. The primary objective is to enhance the accuracy of predicting the compressive strength (CS) of fly ash-based (FA) geopolymer concrete (GPC). The dataset employed encompasses comprehensive material and chemical information, facilitating a predictive approach linking factors to strength. Rigorous preprocessing techniques are employed to eliminate outliers and ensure data integrity. Multivariate analyses are executed to visually represent the dataset's structure. The development of the hybrid ensemble model is realized through a stacking strategy, integrating the predictive capabilities of individual models. Thorough evaluation using diverse statistical metrics validates the superiority of the hybrid model compared to standalone base models, underscoring its enhanced precision in CS prediction for FA-based GPC. Sobol and FAST global sensitivity analysis was also employed to find the influence of input parameters on strength. Extra water content and curing temperature with Sobol indices of 67.2% and 42.5%, and FAST indices of 65.2% and 45% were found to be the most sensitive parameters of the studied database. Among the chemical constituents of binders and activators, the SiO2 content and CaO content of FA exhibited greater sensitivity, impacting the CS. On the other hand, the Na2O, Al2O3, and Fe2O3 content of fly ash and the SiO2 and Na2O percentage of sodium silicate were found to have a relatively lower impact.

Enhancing the properties of geopolymer concrete using nano-silica and microstructure assessment: a sustainable approach

Nowadays low calcium fly ash-based geopolymer concrete can be replaced with cement-based concrete to avoid the adverse effect of manufacturing cement on the environment. Utilization of geopolymer concrete instead of traditional concrete using low calcium fly ash and nano silica reduces a significant amount of CO­2 emission towards the atmosphere. However, the performance of geopolymer concrete is less than that of Portland cement concrete. To improve the performance of geopolymer concrete nano silica was used in the present study. In this work, geopolymer concrete was made utilizing fly ash, ground granular blast furnace slag (GGBS), and sugarcane bagasse ash. In the first instance, binary combinations i.e. fly ash and GGBS were employed as cementitious materials for the production of geopolymer concrete. In the second instance, a ternary mixture of pozzolanic material was prepared by taking 25% GGBS, 65% Fly ash, and 10% bagasse ash. In the third instance, varying percentages of nanoparticles were used for the above ternary mixture. The mechanical and durability properties of the geopolymer composite that was made earlier were tested. The compressive strength and split tensile strength of geopolymer composites were assessed for mechanical properties and a rapid chloride permeability test, water absorption test, and acid attack test were done to know about the porosity of concrete. Results showed that, with a dose of 4% nanoparticles, the durability and strength properties of the concrete had improved the most. The GCBA-N4 mixture had the highest split tensile and compressive strength was measured to be 2.91 MPa and 41.33 MPa and the rapid chloride permeability test, water absorption rate, and percentage of mass loss due to sulfate attack were found as a minimum for GCBA-N4 specimen.

Effect of Micro Lime on The Ambient Cured Sugarcane Bagasse Ash-Based Geopolymer Concrete

Geopolymer concrete has been the ideal replacement for Ordinary Portland cement concrete in producing green concrete. The binder in geopolymer concrete is a cementitious paste made from amorphous Aluminosilicate and activated by an Alkaline solution. The geopolymerization process is initiated at elevated temperatures. Thus, the curing requires elevated temperatures. This curing method limits the application of geopolymer concrete in the construction industry. In a geopolymer mix, the presence of Calcium ions allows the formation of Calcium Aluminate Silicate and Calcium Silicate Hydrate gels, allowing ambient temperature curing. Therefore, this study investigates the effect of micro lime on the Sugarcane Bagasse Ash-based geopolymer concrete. The micro lime was added to the geopolymer concrete in 1, 3, 5 and 7% by the Sugarcane Bagasse Ash weight. A mix design was based on a Densified Mix Design Algorithm. The tests carried out included compressive strength and water absorption. Ambient curing of the SCBA-based geopolymer concrete was achieved with 1% of the micro lime. The compressive strength increased with the increase of the micro lime, 10N/mm2 at 1%, to 18.25N/mm2 at 7% micro lime. The ambient temperature-cured geopolymer concrete at 3% micro lime had the lowest water absorption rate.

A Proposed New Mix Proportioning Method for Fly Ash-Based Geopolymer Concrete

A Proposed New Mix Proportioning Method for Fly Ash-Based Geopolymer Concrete

Prediction of Compressive Strength of Fly Ash-Based Geopolymer Concrete Using Supervised Machine Learning Methods

Prediction of Compressive Strength of Fly Ash-Based Geopolymer Concrete Using Supervised Machine Learning Methods

Effect of graphene nanoplatelets on engineering properties of fly ash-based geopolymer concrete containing crumb rubber and its optimization using response surface methodology

The research aims to investigate the effect of graphene nanoplatelets (GNPs) on mechanical properties, workability as well as microstructure of fly ash-based geopolymer concrete containing crumb rubber (CR) through experiments and response surface methodology (RSM). A total of 20 mix designs were utilized, with 10–30% volume replacement of fine aggregate with CR and addition of 0.1–0.4% GNPs by weight of binder. All mix designs were studied for attributes including slump flow, compressive strength, stress-strain behavior, modulus of elasticity, tensile strength, flexural strength, toughness, impact resistance, water absorption, and porosity. Morphological changes due to crack formation, microstructure, and interfacial interaction between aggregate and mortar were evaluated using field emission scanning electron microscopy (FESEM). Vickers microhardness tests were carried out from the surface of aggregate towards the matrix to evaluate the interfacial transition zone. Results indicated that CR replacement reduced the mechanical properties of geopolymer concrete, while GNPs inclusion mitigated the negative effects of CR and significantly enhanced the properties of the geopolymer concrete. Results also revealed that 0.3% addition of GNPs increased the compressive strength, elastic modulus, tensile strength, and flexural toughness of the concrete containing the CR. Moreover, addition of 0.3% GNPs in specimens having 30% CR enhanced the average microhardness by 34%, which demonstrates that GNPs addition improved the matrix compactness and interfacial transition zone between CR and matrix. Multi-objective optimization with RSM was accomplished for the combined use of CR and GNPs in fly ash-based geopolymer concrete. RSM results showed that combination of 10% CR and 0.2% GNPs is the best combination for achieving the highest strength properties with the lowest percentage of GNPs.

Low-carbon enhancement of fly ash geopolymer concrete: Lateral deformation, microstructure evolution and environmental impact

To provide a more environmentally friendly alternative to conventional cement-based concrete, the use of fly ash based geopolymer concrete (FGC) has been explored. However, FGC typically requires high-temperature curing to achieve optimal material performance, which results in significant energy consumption and carbon emissions, leading to negative environmental impacts. To address this issue, a small amount of ordinary Portland cement (OPC) has been added to FGC, facilitating its setting and hardening at room temperature. At four different ages, a series of basic mechanical properties were tested, including Poisson's ratio. At 28 days, the resulting OPC-FGC has demonstrated comparable polymerization reactions and mechanical properties to heat-cured FGC, including lateral deformation ability and compressive behavior. Microscopic tests have shown that OPC-FGC has a denser matrix and a more reasonable pore structure distribution over time than heat-cured FGC. Furthermore, a life cycle assessment has indicated that OPC-FGC has a lower negative impact than heat-cured FGC. These findings suggest that OPC-FGC can be a viable substitute for conventional cement-based concrete, providing both mechanical properties and environmental benefits in engineering applications.

Influence of marine environment on durability and microstructural properties of fly ash-based geopolymer concrete

Influence of marine environment on durability and microstructural properties of fly ash-based geopolymer concrete

Evaluation of durability and microstructure evolution of chloride added fly ash and fly ash-GGBS based geopolymer concrete

The evaluation of corrosion behaviour of rebar and changes in microstructure evolution in geopolymer concrete (GPC) in the presence of chloride ions form an important aspect of durability investigation. For this purpose, an experimental investigation was undertaken to examine the corrosion of reinforcing steel and changes in microstructure development of fly ash based geopolymer concrete (FGC) and fly ash-GGBS based geopolymer concrete (FSGC) containing chloride ions. Corrosion behaviour was evaluated through corrosion potential (Ecor) and corrosion current density (Icor) and microstructural changes of GPC were examined at various ages and that at rebar level by XRD, EDS, FTIR, and FESEM analyses. Test results revealed that chloride ions had significant influence on consistency, strength, and microstructure of GPC. NaCl improved the consistency of GPC mixes. FSGC mixes showed 38.1% to 114.2% higher strength than FGC mixes at all ages irrespective of NaCl concentration. Further, GPC mixes exhibited lower strength with increase in NaCl concentration at all ages. Rebar embedded in FSGC specimens exhibited mostly less negative Ecor and lower Icor compared to FGC specimens. Results of chloride analysis revealed lack of chloride binding in GPC mixes. Higher peak intensity of aluminosilicate gels and presence of C-S-H gel in FSGC mixes as identified from XRD analysis and higher atomic Ca/Si ratio in FSGC mixes obtained from EDS analysis confirmed the improved performance of FSGC mixes in terms of higher strength, lower corrosion activity and lower chloride content over FGC mixes.

Hydration, Microstructure, and Properties of Fly Ash–Based Geopolymer: A Review

Abstract Geopolymers have gained attention as a potential eco-friendly alternative to Portland cement, primarily due to their reduced carbon dioxide emissions and the opportunity to repurpose industrial waste materials. Fly ash (FA), a byproduct of coal combustion, has been favored as a raw material for geopolymer concrete owing to its widespread availability and high concentrations of alumina and silica. The development and application of fly ash–based geopolymer concrete can contribute significantly to production of sustainable construction materials. An in-depth analysis of fly ash–based geopolymer concrete has been conducted to explore its potential as a substitute for traditional concrete. This review encompasses the underlying reaction mechanism, strength, long-term durability, and microstructural characteristics of geopolymer concrete. The present review paper shows that adding the optimal quantity of fly ash improves the performance of fly ash–based geopolymer when exposed to extreme durability conditions, as well as improving strength properties. The microstructural analysis shows that when fly ash is added, the microstructure of the concrete matrix would be dense and packed. However, challenges remain in adopting fly ash–based geopolymer concrete for large-scale construction projects, as the existing literature presents inconsistencies in the reported strength, durability, and test results. Further research is necessary to consolidate knowledge on the behavior and mechanism of fly ash–based geopolymer concrete and to ultimately provide comprehensive data to support its widespread implementation in the construction industry.

Effect of curing conditions on the compressive strength of fly ash-based geopolymer concrete

The utilization of Ordinary Portland Cement (OPC) in concrete construction has led to significant environmental concerns, including the depletion of natural resources and the release of CO2 emissions during its production. To address these issues, the development of cement-less concrete known as geopolymer concrete (GPC) offers a promising solution. GPC can be produced by utilizing industrial waste materials, thereby promoting environmental sustainability. In this study, fly ash, an industrial waste, was used as a key component in the production of GPC.The research focused on investigating the effects of various variables on the workability and compressive strength of GPC. Specifically, the molarity of sodium hydroxide (NaOH) solutions (6 M, 9 M, 12 M, and 14 M), curing temperatures (30 °C, 60 °C, and 90 °C), and curing periods (7, 14, and 28 days) were examined. The performance of GPC was compared to that of OPC-based control concrete.The results obtained from the experiments exhibited promising outcomes, highlighting the potential of fly ash-based GPC as an alternative to OPC-based concrete. The study revealed that GPC achieved desirable workability and compressive strength when subjected to specific combinations of the examined variables.By utilizing fly ash as an industrial waste material, GPC not only addresses environmental concerns associated with OPC but also contributes to sustainable construction practices. The findings of this study provide valuable insights into the feasibility of utilizing fly ash-based GPC as a viable alternative to OPC-based concrete, emphasizing its potential for reducing environmental impact in the construction industry.

A novel multi-criteria comprehensive evaluation model of fly ash-based geopolymer concrete

Fly ash-based geopolymer concrete (FA-GPC), which has better early mechanical properties, durability and environmental impact, is recognized as a low-carbon concrete that has a high potential to replace ordinary Portland cement concrete. Although scholars have analyzed the mechanical properties, durability performance and environmental impact of FA-GPC independently, few studies have considered the above properties comprehensively to guide the material selection. In this study, choosing compressive strength, sulfate erosion resistance and environmental impact, including global warming potential (GWP), acidification potential (AP), primary energy depletion (PED), as evaluation indicators to be tested and analyzed with 9 different mixtures by Life Cycle Assessment (LCA) method. Based on the gray clustering analysis (GCA) method, we established a comprehensive evaluation model, then applied the commonly used Multi-criteria decision-making (MCDM) methods, namely TOPSIS and VIKOR, to observe the conclusions of the different evaluation methods. The results indicated that: (1) Experiments on compressive strength and sulfate erosion resistance and analysis of environmental impact show that FA-GPC has good sulfate erosion resistance, the alkaline activated solution is not only the most significant factor affecting the compressive strength, but also the biggest contributor to the environmental impact. (2) The evaluation models developed successfully selected the optimal mix ratio for a given function. Although the ordering of the three methods is not the same, because they have different optimization and ranking mechanisms of GCA, TOPSIS, and VIKOR, they come to the same conclusion indicating alternative A3 is optimal. The ranking of alternatives is influenced by the preferences of decision-makers, especially those at the intermediate level.

Durability performance of low calcium Flyash-Based geopolymer concrete

This investigation aims to systematically evaluate the durability performance of 30 MPa grade of low calcium fly ash-based geopolymer concrete. The geopolymer concrete with fly ash as binder is manufactured using an alkaline activator solution (of 14 Molar and Na2Sio3/NaOH ratio of 2.5). The results were also compared with the Portland cement concrete of similar grade. The concrete samples were subjected to water absorption, water permeability, sorptivity, acid resistance, sulphate resistance, and rapid chloride penetration tests. Water absorption study findings revealed less water absorption by low calcium fly ash-based geopolymer concrete than Portland cement concrete. Also, the water permeability tests on geopolymer concrete indicated lower water penetration depth compared to Portland cement concrete. Sorptivity test results depict lower sorptivity by geopolymer concrete over ordinary Portland cement concrete. Geopolymer concrete shows better acid resistance and sulphate resistance performance than Portland cement concrete in terms of residual compressive strength. Rapid chloride penetration test results indicated moderate chloride penetrability of geopolymer concrete and low chloride penetrability by Portland cement concrete. In general, low calcium fly ash based geopolymer concrete outperformed Portland cement concrete in most durability indices, which led to the conclusion that low calcium fly ash based geopolymer concrete durability performance was superior to that of concrete of a similar grade made of Portland cement concrete.