Metakaolin-based Geopolymer Concrete Research Articles

Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method

Abstract Geopolymer in recent concrete (GP) has gained significant attention due to its sustainability and environmental friendliness. Local metakaolin-based geopolymer is weaker than geopolymers made from other materials due to its low Si/Al ratio. A consistent mixture design is also lacking because geopolymers are affected by many variables. This study presents a method to find the optimal geopolymer mixture based on locally modified metakaolin as a source of aluminates and silicates using the Taguchi method. Metakaolin was modified using different contents of materials rich in silica, such as silica fume (SF), or materials rich in calcium, such as calcium oxide (CaO) of 5, 10, and 15%. The inclusion of 5% SF, 10% CaO, and a combination of 5% SF and 5% CaO as substitutes for metakaolin increases the compressive strength by 16.8, 6.9, and 22.8%, respectively, compared to the reference mixture without any modifications. In other words, adding 5% SF and CaO increased the molar ratio of SiO2/Al2O3 (R) from 1.782 to 1.914, resulting in the highest compressive strength of 53.3 MPa after 7 days of sun curing. To obtain the optimal mixture that achieves the highest compressive strength, the impact of three main variables, including the concentration of sodium hydroxide (SH), alkali solution-to-binder (Al/B) ratio, and sodium silicate-to-sodium hydroxide (SS/SH) ratio, must be considered using Taguchi method. A total of nine mixtures were investigated. It was found that 13 M of SH, 0.65 Al/B, and 2.5 SS/SH give a high compressive strength of 58.6 MPa at 7 days. Also, it was found that the concentration of SH plays a more important role in increasing the compressive strength than the alkali-to-binder ratio and SS/SH ratio. The scanning electron microscopy images show that the 5% weight replacement of metakaolin by silica and CaO could source fewer and smaller pores and reduce the microcracks’ width.

Effects of Waste Plastic and Glass Aggregates on the Strength Properties of Ambient-Cured One-Part Metakaolin-Based Geopolymer Concrete

The production of Portland cement (PC) is associated with carbon emissions. One-part geopolymer “just add water” is a user- and environmentally-friendly binder that can potentially substitute PC. However, there is limited research on the setting time, fresh, and strength properties of one-part metakaolin (MK)-based geopolymer concrete (OMGPC) incorporating recycled aggregates. Hence, the study explored the fresh, mechanical (compressive, flexural, splitting tensile, and E-modulus) and microstructural properties of ambient cured (7-, 28-, and 90-day) OMGPC containing recycled waste plastics (RESIN8) and recycled fine waste glass aggregate (FWG) at 5% and 10% by volume of the sand. The study result shows that 2% trisodium phosphate by wt. of the binder retard the initial and final setting times of OMGPC. At the same time, the incorporation of RESIN8 and FWG aggregates improved the workability of geopolymer concrete. The lightweight properties of RESIN8 aggregate reduce the hardened density of OMGPC, while the FWG specimens show a similar density to the control. The compressive strength of RESIN8 and FWG OMGPC range from 19.8 to 24.6 MPa and 26.9 to 30 MPa, respectively, compared to the control (26 to 28.9 MPa) at all curing ages. The flexural and splitting tensile strength of the OMGPC range from 2.2 to 4.5 MPa and 1.7 to 2.8 MPa, respectively. OMGPC is a viable alternative to Portland cement, and FWG can substitute sand in structural concrete by up to 10% and RESIN8 aggregate at 5% by volume of the natural sand.

The use of machine learning techniques to investigate the properties of metakaolin-based geopolymer concrete

The construction industry significantly contributes to global greenhouse gas emissions, highlighting the imperative for developing environmentally friendly construction materials. Geopolymers, particularly those utilizing metakaolin (MK), have emerged as a promising green alternative to conventional concrete. However, the acquisition of MK-based geopolymer concrete with optimal mechanical properties poses challenges due to numerous influential factors, disagreement over various findings, and the lack of a reliable predictive model. This study aimed to address this gap by employing a wide range of machine learning methods, namely gradient boosting machine, random forest, decision tree, artificial neural network, and support vector machine. Different optimization and regularization techniques were used to comprehensively understand the factors affecting the compressive strength of MK-based geopolymer concrete, including mixture design, chemical characteristics of the initial binder and activators, and different curing regimes. The results demonstrated the exceptional performance of the gradient boosting machine in predicting the compressive strength of MK-based geopolymer concrete, achieving a coefficient of determination of 0.983 and a mean absolute error of 1.615 MPa. Additionally, the study employed partial dependence plots, feature importance analysis, and SHapley Additive exPlanations (SHAP) to elucidate the proposed models. The coarse-to-fine aggregate ratio, H2O/Na2O molar ratio, extra water content, and sodium hydroxide concentration were identified as the most critical parameters affecting the compressive strength of MK-based geopolymer concrete. This research contributes to advancing the development of sustainable construction materials, streamlining experimental tasks, minimizing the need for labor and materials, improving time efficiency, and providing valuable insights for optimizing the design of MK-based geopolymer concrete.

Effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete

Carbonation curing can absorb CO2 and fix it as a carbonate mineral in cementitious materials. Carbonation curing in Portland cement-based materials has been widely discussed in the literature, unlike carbonation curing in geopolymers. Therefore, the objective of this article was to evaluate the effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete. Changes in pH value, carbonation depth, CO2 absorption, compressive strength, and microstructure formation were determined before and after carbonation curing. The results showed that the carbonation depth of Portland cement concrete is similar to the carbonation depth of geopolymer concrete. Furthermore, compressive strength after post-conditioning was not affected by carbonation curing, remaining statistically equal to reference concrete. Also, the formation of carbonates (Na2CO3 and CaCO3) refined the pore structure and increased closed pores, reducing the void ratio and the water absorption (permeability properties). A hybrid system containing N-A-S-(H) gel and carbonate crystals was identified.

Influence of reclaimed asphalt pavement aggregate on the performance of metakaolin-based geopolymer concrete at ambient and elevated temperatures

Considering the environmental concerns surrounding conventional cement concrete production and the increasing demand for more sustainable and green materials, recent research considered utilization of recycled waste materials (e.g., aggregates from concrete construction and demolition, and reclaimed asphalt pavement) as full or partial substitutes for natural aggregates. Another direction of the research considered the production of more sustainable binders as an alternative to conventional cement (e.g., geopolymer or alkali-activated materials).To serve the objective of utilizing waste materials and reducing negative environmental impact associated with the use of cement concrete, the present study investigated the potential of producing metakaolin-based geopolymer concrete incorporating reclaimed asphalt pavement (RAP) aggregate. This research comprised experimental testing of five concrete mixes with 0%, 25%, 50% and 100% coarse RAP aggregate replacing the natural aggregate. Tests included compressive stress–strain behavior at ambient conditions (i.e., compressive strength, elastic modulus, strain at peak strength and toughness), and flexural strength. The performance after heat exposure to elevated temperatures of 300 °C and 600 °C was also tested. Proposed models for predicting the elastic modulus, strain at peak strength, flexural strength, and compressive stress–strain relationship matched the experimental results well. Results indicated that natural aggregate replacement by 25 % RAP aggregate caused a reduction in the compressive and flexural strengths by 42.8% and 26.2%, respectively. The increase in the RAP aggregate content enhanced the strain at peak strength e.g., the strain at peak strength was 42.9% higher than the control mix when 100% RAP aggregate was utilized.

Sustainable Alternatives to Cement: Synthesizing Metakaolin-Based Geopolymer Concrete Using Nano-Silica

The emission of carbon dioxide gas from the cement manufacturing industry has raised concerns about global warming. Geopolymer concrete (GC) is gaining attention as a sustainable and environmentally friendly alternative to traditional cement concrete. The current study focused on using local clay to synthesize and characterize metakaolin-based GC with varying percentages of nanosilica (NS) (1.5%, 3.0%, 4.5%, 6.0%, and 7.5% by weight of MK content) using NaOH/sodium silicate. The geopolymer specimens were cured at room temperature for 28 days, and their workability, compressive, tensile, and flexural strengths were measured to evaluate the influence of NS on the concrete’s mechanical properties. The study found that the compressive, tensile, and flexural strengths of the GC increased gradually up to 6.0% NS, but any further increase in its ratio resulted in a reduction in mechanical characteristics. The study concludes that the addition of 6.0% NS in metakaolin (MK)-based GC produces the highest mechanical properties, improving the compressive strength of the GC mix by 34.3% compared to the control GC mix and improving the flexural and split tensile strengths by 39% and 37%, respectively, compared to control GC strengths. Furthermore, the statistical analysis confirms nano-silica’s significant impact on geopolymer concrete’s mechanical properties, emphasizing its role in improving performance and sustainability as an alternative to cement-based materials.

Effect of anisotropy on permeability index and water absorption of 3D printed metakaolin-based geopolymer concrete

3D-printed geopolymer concrete (3DPGPC) is being showcased as a potential alternative to ordinary Portland cement concrete in digital construction. However, the widespread application is limited due to the unknown long-term durability properties of the material, which could also be influenced by the anisotropic behaviour of the prints. The durability index (DI) of metakaolin (MK) based 3DPGPC and mould-cast specimens from mixes modified with 0% and 5% slag and reinforced with 0.5% polypropylene fibre by volume are investigated using the oxygen permeability index (OPI) and water absorption test. 70 mm diameter by 30 mm thick specimens were cored perpendicular (D3-horizontal and D2-vertical) to the printing direction. OPI specimens were cured for 28 and 90 days, respectively, in the climate-controlled room at 23 (±2°C) and 65 (±5%) relative humidity. 7 days before curing elapsed, specimens were placed in the oven and maintained at 50 ℃. Specimens were removed from the oven and cooled to 23 (±2°C) in the desiccator for 2 h before placing them in the permeameter cell for testing at 28 and 90 days of curing following SANS-3001-CO3-3 (2015). The OPI test comprised the supply of oxygen at the pressure of 120 kPa to the permeameter cell and testing terminated when the pressure dropped to 50 kPa. Also, the water absorption of mould cast and 3DPGPC specimens were determined following ASTM D570. The water absorption and permeability coefficients of 3DPGPC are compared with mould-cast to contextualise the durability of 3DPGPC. Slag inclusion reduced the permeability index of mould-cast and 3DPGPC at 28-and 90-day curing ages. However, mould-cast specimens had better OPI performance than 3DPGPC. D3 specimens are less permeable than D2. Also, mould-cast specimens exhibited lower water absorption characteristics than printed specimens. The OPI and water absorption tests indicate different migration characteristics under one-dimensional ingress in 3DPGPC in orthogonal directions.

Effect of curing conditions on physico-mechanical properties of metakaolin-based geopolymer concrete containing calcium carbide residue

Effect of curing conditions on physico-mechanical properties of metakaolin-based geopolymer concrete containing calcium carbide residue

Characterization study of geopolymer concretes fabricated with clinker aggregates

Geopolymers are a new generation of building material that has recently been popular in reducing carbon emissions. As a result of its amorphous alumina-silicate-based reaction product, it has many superior properties. This study investigated the mechanical and physical properties and high-temperature resistance of ground-granulated blast furnace slag and metakaolin-based geopolymer concrete fabricated with clinker aggregates produced in a short curing time (8 h). In alkali activators, the sodium silicate to sodium hydroxide (SS/SH) mass ratios were 2, 2.25, 2.5 and 2.75. Two curing methods were used, namely ambient (25 °C) and oven curing (80 °C). The observed unit weights vary between 2275–2392 kg/m3 for the samples of the geopolymeric composites. Porosity and water absorption vary between 4.92 and 8.84% and 3.58–7.26%, respectively. The heat curing application decreased the mixtures' water absorption, unit weight, and porosity values. The compressive strength of the samples subject to ambient curing varied between 39.2 and 59.8 MPa. Withal, the samples cured at 80 °C for 8 h were between 66.9 and 112.4 MPa. The increased SS/SH ratio also increased the observed strength values. Capillary water absorption of all samples is below 0.6 kg/m2. Heat-cured geopolymers decreased capillary water absorption to 0.1 kg/m2. The weight loss after high temperature decreased as the SS/SH ratio increased. The N-A-S-H gel in the zeolitic structure was observed in SEM analysis. The FT-IR analysis visualized the carbonation in the heat-cured mixtures. As a result, over 100 MPa compressive strength values were observed with the clinker aggregates at 80 °C after 8 h of curing time. Withal, a high-temperature refractory composite was developed with the clinker aggregates. Moreover, the nuclear radiation shielding abilities of geopolymer concretes were investigated experimentally. The gamma shielding parameters of the samples were evaluated by transmission measurements in the range of 0.081–0.661 keV. Also, neutron dose measurements were performed, and the samples produced as neutron attenuator capacity was evaluated. The radiation shielding capabilities were improved slightly with increasing sodium silicate solution content.

Preparation and validation of sustainable metakaolin based geopolymer concrete for structural application

Geopolymer is one of the trending research areas in composite materials; there are many areas in geopolymer that unexplored still need to be explored. In this paper, an attempt is made to explore such an area and develop high-performance concrete. The optimal percentage of slag and activators, such as potassium and calcium hydroxide ratio, were investigated in metakaolin-based geopolymer. At ambient conditions, alkaline to binder (A/B) ratios of 0.25, 0.35, and 0.45 were used to cast the different proportions of geopolymer concrete at ambient conditions when tested at 7, 28, and 90 days. The fresh, mechanical properties, probability, matrix andsmoothening plot for modulus of elasticity of geopolymer were investigated. Ishikawa diagram,which signifies cause-and-effect factors of geopolymer concrete is discussed. Geopolymer was observed to have medium workability and mechanical properties and showed excellent results compared with traditional concrete at 30 % slag usage at a 0.35 ratio of A/B. At 30 % of GGBS, geopolymer concrete optimum mix maximum strength was observed.trix Matrix, and smoothening analysis show that linear relationships vary among the parameters used for analyses.

Experimental investigation on the durability of metakaolin-based geopolymer concrete in aggressive environments

The properties and performance of geopolymer concrete have been evaluated in numerous studies in recent decades. One of the fields of study is the evaluation of the durability of geopolymer concrete in aggressive environments. In this study, the influence of four experimental factors, including curing temperature (T), the weight ratio of sand to metakaolin (S/M), aggressive environment type (AE), and aggressive environment exposure time (Et) were investigated on the durability and mechanical properties of metakaolin-based geopolymer concrete (MGPC). Moreover, 5% sulfuric acid solution, 5% sodium chloride solution, and Persian Gulf seawater were used as aggressive environments. Response surface methodology (RSM) was implemented to statistically design and analyze the experiments. Mathematical models were derived for the prediction of residual compressive strength (RFc), weight changes (∆W), and compressive strength changes (∆Fc) of MGPC. The analysis of variance showed that all four factors had a significant effect on the responses, while only AE-S/M and AE-ET factors had an interaction. Design-Expert software (DX7) was employed for the optimization of design factors. Results revealed that the use of the optimum weight ratios of S/M (2.52, 2.07, and 1.29) at a curing temperature of 46 °C and an exposure time of 56 days led to RFc values of 34.12, 43.60, and 44.15 for sulfuric acid, sodium chloride, and Persian Gulf seawater aggressive environments, respectively. These results, which are higher than the minimum required compressive strength of concrete, along with the ∆Fc and ∆W values, confirm the acceptable durability of MGPC.

Long-term mechanical characteristics of fibre reinforced metakaolin-based geopolymer concrete: A review

The colossal appeal of eco-friendly and sustainable concrete has made researchers find a substitute for Portland cement concrete. Therefore, geopolymer is an innovativeand environmentally beneficial binder material that was developed to reduce Portland cement's harmful environmental consequences. Also, it is seen that certain properties are shared by both Portland cement concrete and geopolymer concrete including brittleness. Hence, fibres are added to surpass the matrix’s brittleness and improve the tensile, and flexural strength as well as stiffness of concrete. Based on previous research, the primary focus of this study is on the impact of different fibre types on the long-term mechanical performance of geopolymer composites. It also examines the usage of potent pozzolanic metakaolin, which is often added to concrete to increase its mechanical qualities or serve as an alternative for cement. In addition, this study investigated the literature on the effects of fibre characteristics with variable volume proportions on the mechanical strength of metakaolin-based geopolymer concrete. It is seen that geopolymers improved characteristics after fibre addition has opened the door to more research into the material's potential use in various applications.

Properties of modified metakaolin-based geopolymer concrete with crumbed rubber waste from damaged car tires

Waste rubber tires are materials that have a negative impact on the environment. Therefore, it is essential to use waste rubber recycled from damaged tires (CRWA) in geopolymer concrete (GPC) by different partial volumetric replacements to natural coarse aggregate (0, 10, 20, 25%) after preparation to a gradation similar to that for natural coarse aggregate. Calcium oxide and silica fume were substituted in metakaolin (MK) at 5 wt%. The GPC mix consisted of MK after modification, coarse aggregate, fine aggregate sodium hydroxide solution, sodium silicate solution, superplasticizer, and extra water, with quantities of 372, 911, 83, 192, 4, and 52 kg/m3, respectively. It is clear from the experimental results that the mechanical properties of geopolymer concrete decreased with the increase in the content of the crumbed rubber waste aggregate. The compressive, splitting tensile, and flexural strengths decreased by approximately 38.6, 44.6, and 52.6%; 10.6, 15.2 and 21.2%; and 6.25, 12.75, and 16.5% when the crumbed rubber aggregate was 10, 20 and 25%, respectively. In addition to recycling the rubber waste from damaged tires, desirable properties can be obtained, starting from not using water in curing GPC and rapid strength development at early ages. There is a clear improvement in the thermal properties and weight of GPC containing CRWA by reducing the thermal conductivity and dry density by including 10, 20, and 25% CRWA compared with the reference GPC without this waste material.

Investigating the Properties of Foamed Fly Ash and Metakaolin-based Geopolymer Concrete

A study has been carried out to produce environmentally friendly lightweight concrete by total replacement of cement with fly ash and metakaolin as binder material by adopting the pre-formed foam method. In this research, a geopolymer paste was produced by mixing fly ash or metakaolin with an alkali solution of sodium silicate and sodium hydroxide. Five mixes were produced at a density of 1000 kg/m³ as four foamed geopolymer concrete and one conventional foamed concrete made with cement paste as a binding medium. During the laboratory work, many trials were carried out to solve the segregation of the cellular structure from the mortar. From the results, it was noticed that the pore merging is more evident in foamed concrete mixes rather than in foamed geopolymer concrete mixes. In addition, the pore structure of fly ash-based geopolymer concrete is finer than that of metakaolin-based concrete geopolymer. The greater degree of pore merging resulted in forming of larger irregular voids and wider distribution of pore sizes and finally reducing strength. In general, the permeation, mechanical and thermal properties of foamed mixes made with geopolymer pastes are better than those of foamed mix made with cement paste. For a geopolymer paste, using metakaolin and fly ash C in combination helped in achieving the best properties i.e. reduction in water absorption by 34%, increasing strength by 78% and decreasing thermal conductivity by 44%.

Evaluation of structural performances of metakaolin based geopolymer concrete

Last few decades, there has been a substantial advancement of geopolymer (GP) as a Portland cement substitute. It is vital to investigate potential building uses for geopolymer concrete (GPC). Six different mixes were cast for an alkaline to binder (A/B) ratio of 0.25–0.50 with an interval of 0.05. Metakaolin-based geopolymer were cured at ambient temperature and tested for 7, 14, 28, and 90 days. Metakaolin-Marble (MM00) mix was observed to have a maximum slump. For an A/B ratio of 0.35, maximum compressive, split tensile, flexural strength and modulus of elasticity was achieved. For elevated temperature resistance, geopolymer concrete cubes were exposed to temperatures (T) of 200, 400, to 600 C. As the temperature increased, compressive strength (CS) reduced. As the increase of the alkaline to binder (A/B) ratio, the strength of geopolymer concrete increases up to a specific limit beyond the limit strength decline. An empirical formula for split tensile (STS) value prediction using compressive strength values is proposed, valid for determining split tensile strength value. The correlation between compressive strength, split tensile strength, flexural strength, and bulk density varies linearly for a quadratic polynomial.

Eco-friendly geopolymer concrete based on metakaolin and ceramics sanitaryware wastes

The sanitary ceramics industry generates huge quantities of wastes notwithstanding all the efforts made to improve the manufacturing process. The aim of the present work is to investigate the potential reuse of sanitary ceramics wastes as an aggregate to manufacture metakaolin based geopolymer concrete. The effect of granulometry and added quantity of SCW on the properties of metakaolin based geopolymer matrix was assessed via physical, mechanical and microstructural properties. the results indicate that the developed concretes exhibit higher mechanical performance compared to conventional concretes and to reference geopolymer. It was also shown that the increase in aggregate particle size had a significant influence on the compressive strength as well as the density and porosity. The microstructure in the interfacial transition zone (ITZ) between the recycled ceramic aggregate and the paste was observed to be more compact.

The radiation shielding and microstructure properties of quartzic and metakaolin based geopolymer concrete

Today, binders with low CO2 emissions are preferred in building design. Geopolymers have lower CO2 emissions than conventional concrete and Portland cement. This study investigated the efficiency of geopolymers produced with short curing time and low curing temperature against gamma and neutron radiation. Ground blast furnace slag (GBFS), metakaolin and quartz powder were used as binders to produce geopolymers. In addition, 200, 400 and 800 kg/m3 quartz sand (with high SiO2 content) was used instead of river aggregate in the mixtures. Geopolymers were cured at 40, 60 and 80 °C for 6, 8 and 10 h. The hardened unit weights of geopolymers vary between 2160–2346 kg/m3. As the quartz sand content increased, the hardened unit weight of the mixtures increased. As the curing temperature increased, the unit weight of the mixtures decreased as the evaporation increased. The compressive strength of geopolymers varies between 40.3 and 153.9 MPa, and the flexural strength varies between 3.3 and 8.8 MPa. As the curing temperature and time increase, the mechanical properties of the mixtures improve as the geopolymerization increases. In addition, if quartz sand is used instead of river sand, the compressive strength can increase up to 40%. With the increase of quartz sand content, the capillarity coefficients of geopolymers decrease. Capillarity coefficients of geopolymer mixtures are below 0.10 kg/m2.min0.5. Besides, fast neutron/photon radiation-shielding features of the geopolymers were examined, experimentally. The M3 sample is more accomplished at absorbing gamma photons due to its higher GBFS content. The M1 sample with the highest concentration of quartz sand is the most effective sample at attenuating fast neutrons and has a better ƩR value to some commonly used neutron attenuators. As a result, it has been shown that geopolymers with a compressive strength of about 160 MPa can be produced after 10 h. This study also revealed that M1 and M3 samples can be put to good use for protection from fast neutron and gamma-ray radiations, respectively, and new geopolymer materials can be designed as shielding materials.

Influence of Coarse Aggregate Size on the Bonding between CFRP Sheets and Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Influence of Coarse Aggregate Size on the Bonding between CFRP Sheets and Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Effect of Waste Clay Brick on the Modulus of Elasticity, Drying Shrinkage and Microstructure of Metakaolin-Based Geopolymer Concrete

Effect of Waste Clay Brick on the Modulus of Elasticity, Drying Shrinkage and Microstructure of Metakaolin-Based Geopolymer Concrete

Investigation of the Effects of Nano Silica Particles and Zeolite on the Mechanical Strengths of Metakaolin-Based Geopolymer Concrete

Due to its unique qualities, concrete is the most extensively utilized substance in the construction sector after water. However, because one ton of Portland cement produces about one ton of CO2, the Portland cement manufacturing process has considerable disadvantages. As a result, an alternative to Portland cement appears to be required. Geopolymer is a new and environmentally friendly cementitious material that can be used in place of Portland cement. Chemically and mechanically, geopolymer concrete outperforms traditional concrete. The weight ratio of water to dry matter used in polymerization, as well as the weight ratio of sodium silicate to NaOH solution, have an impact on the compressive strength of geopolymer concrete. As a result, additional research into these variables appeared to be necessary. This paper specifically looked at how nanosilica and zeolite affected the mechanical strength of metakaolin-based geopolymer concrete. Nanosilica was added to metakaolin-based geopolymer concrete to improve mechanical characteristics. Furthermore, using zeolite in a metakaolin-based aluminosilicate source lowers the mechanical strength of geopolymer concrete while also lowering the cost. The optimal weight ratios for polymerization water to dry matter and sodium silicate solution to NaOH solution were 0.4741 and 1.5, respectively, resulting in maximum compressive pressures of 3, 7, and 28 days.