Metakaolin Geopolymer Research Articles

Strength and Microstructure Characteristics of Metakaolin-Based Geopolymer Mortars with High Water-to-Binder Ratios

Geopolymers and other alkali-activated materials were investigated in detail as alternatives to ordinary Portland cement because of their reduced CO2 emissions, high (radionuclide) binding capacities, and low permeabilities. The last two properties make them potential materials for the immobilization of several types of chemical waste. In this context, the direct immobilization of liquid waste streams would be a useful application. This study aimed to develop geopolymers with high water-to-binder ratios, but with good mechanical strengths, while elucidating the parameters that dictate the strengths. Three potential metakaolin geopolymer recipes were cast and cured for 28 days, after which their strengths, mineralogy, and microstructures were determined. The results show that it is possible to attain acceptable mechanical strengths at water-to-binder ratios that vary from 0.75 to 0.95, which is a significant increase from the ratio of 0.55 that is commonly used in the literature. It was found that the most important parameter that governs the mechanical strength is the dilution of the activating solution, which is represented by the H2O/Na2O ratio, while the microstructure was found to benefit from a high SiO2/Al2O3 ratio.

Use of a Piezoelectric Bender Element for the Determination of Initial and Final Setting Times of Metakaolin Geopolymer Pastes, with Applications to Laterite Soils.

This study proposes the use of a non-destructive testing technique, based on piezoelectric bender element tests, to determine the initial and final setting times of metakaolin geopolymer pastes. (1) Background: Metakaolin geopolymer is a new eco-friendly building material that develops strength rapidly and is high in compressive strength. (2) Methods: The initial and the final setting times were investigated via bender element and Vicat needle tests. Metakaolin powder was prepared by treating kaolin at 0, 200, 800, 1000, and 1200 °C. All metakaolin powder samples were then mixed with geopolymer solution at different mixing ratios of 0.8:1.0, 1.0:1.0, 1.2:1.0, and 1.5:1.0. The geopolymer solution was prepared by adding 10 normal concentrations of sodium hydroxide (10 N NaOH) to sodium silicate (Na2SiO3) at various solution ratios of 1.0:1.0, 1.0:1.2, 1.0:1.5, 1.0:2.0, 1.2:1.0, 1.5:1.0 and 2.0:1.0. (3) Results: The optimum temperature for treating metakaolin is established at 1000 °C, with a mixing ratio between the metakaolin powder and the geopolymer solution of 1.0:1.0, as well as a solution ratio between NaOH and Na2SiO3 of 2.0:1.0. (4) Conclusions: The use of piezoelectric bender elements to determine the initial and final setting times of metakaolin geopolymer pastes is a useful method by which to detect geopolymerization by shear wave velocity in a real-time manner. Moreover, the penetration of the Vicat apparatus can confirm the setting times at specific intervals. The relationships between the shear wave velocity and the Vicat penetration appear to be linear, with an initial setting time of 168 m/s and a final setting time of 187 m/s. Finally, the optimum metakaolin geopolymer pastes are applied to improve laterite soils, as measured by CBR tests.

Comparison of bacteria-based self-healing methods in metakaolin geopolymer mortars

This study aims to compare the bacteria-based self-healing methods in metakaolin-based geopolymer mortars. In addition, the effects of Microbially-Induced Calcium Carbonate Precipitation (MICP) on the mechanical properties of metakaolin-based geopolymer mortars were determined in this study. For this purpose, the submersion, spray, and injection methods were utilized for bacteria-based self-healing. The bacterial and bacteria-free medium solutions were used in these methods. In addition, the samples without Sporosarcina pasteurii (S.pasteurii) cells (H), the samples with S.pasteurii cells (M), and the samples with both S.pasteurii cells and the nutrient medium (Z) were prepared according to the microbiological content. Metakaolin-based geopolymer cubes and prisms samples using these contents were produced and cured at room temperature (20 ± 2 °C) for 28 days. Then, cracks were formed in the samples. These cracks on samples were healed using different self-healing methods. Lastly, the mechanical properties of samples were determined. This study showed that the injection method was the most effective method for completely closing cracks. Also, this study found that the M series healed with the injection method had the highest recovery percentage for flexural strength, and it was about 29.69%.

Geopolymer concrete with metakaolin for sustainability: a comprehensive review on raw material's properties, synthesis, performance, and potential application.

In the last three decades, the gigantic demand for sustainable and environmentally friendly concrete with reduced environmental footprints has resulted in the development of low carbon concretes such as geopolymer concrete. Metakaolin which is commonly used as an admixture or partial replacement of cement owing to its most effective pozzolanic properties, which improve the microstructure and strengthen the mechanical and durability properties of cement concrete, has been investigated as a precursor in geopolymer concrete. Several studies have been conducted to comprehend the effect of metakaolin as an additive in geopolymer mortar and concrete prepared with various aluminosilicate sources as precursors such as fly ash and rice husk ash to enhance geopolymerization, densify microstructure, and elevate durability. The present paper recapitulates these investigations primarily concentrating on the various properties of metakaolin-based concrete. The effect of various factors such as alkali content, solids/liquids ratio, alkali reactant ratio, molar ratio, water content, and curing regime has been compiled. Most of them revealed that metakaolin is used as a precursor and yields better geopolymer products. XRD studies reported the peaks demonstrating the development of enhancement in hydration products in comparison to other precursors. Examination of SEM graphs reveals that the addition of a smaller quantity of silica-rich materials densifies the microstructure of geopolymers and produces higher mechanical strength. Durability studies reveal that metakaolin geopolymers possess better water resistance, thermal resistance, and anti-corrosion properties. The possible applications of metakaolin-based geopolymeric materials are also pointed out. The comprehensive knowledge presented here is expected to support the prospective researchers to decide their future course of the research area. Graphical abstract.

Sulfate Resistance and Microstructure of Metakaolin Geopolymer Reinforced by Cellulose Nanofiber and Wollastonite

Sulfate Resistance and Microstructure of Metakaolin Geopolymer Reinforced by Cellulose Nanofiber and Wollastonite

Compressive strength and sulfate resistance of metakaolin-based geopolymer mortar with different ratio of alkaline activator

Geopolymer mortar has been extensively investigated for its application in the construction field.In this paper, the kaolin sourced from Toraget Village, North Sulawesi Province in Indonesia was selected to form a metakaolin-based geopolymer mortar. This was experimentally investigated based on its compressive strength and durability performance, including sulfate resistance.Three variations of the alkaline activator ratio i.e. Na2SiO3/NaOH = 1.5, 2 and 2.5 and the molarity of 10 M NaOH were prepared for testing 7 and 28 days after temperature curing at 60 °C for 4 and 6 h.The method of compressive strength test was conducted based on the American Standard of Testing Materials (ASTM) C109M-21.The results show that the metakaolin geopolymer mortar with an alkaline activator ratio of 2 cured at a temperature of 60 °C for 6 h reached the highest compressive strength with a value of around 30 MPa. In terms of sulfate resistance, metakaolin-based geopolymer mortar with a higher alkaline activator ratio exhibited a higher resistance to compression after immersing the samples in the prepared solutions.Based on the overall results, the alkaline activator ratio of Na2SiO3/NaOH = 2 is recommended for optimizing the metakaolin mortar geopolymer characteristics for further application.

Role of H3po4 Concentration on the Dissolution and Reaction Kinetics of Phosphate Acid Based Metakaolin Geopolymer

Role of H3po4 Concentration on the Dissolution and Reaction Kinetics of Phosphate Acid Based Metakaolin Geopolymer

Effects of Alkaline Activators on Pore Structure and Mechanical Properties of Ultrafine Metakaolin Geopolymers Cured at Room Temperature

Effects of Alkaline Activators on Pore Structure and Mechanical Properties of Ultrafine Metakaolin Geopolymers Cured at Room Temperature

Self-sensing performance of metakaolin geopolymer with carbon nanotubes subjected to repeated compressive loading

Alkaline activated binders showing enhanced piezoresistive properties have recently attracted increased interest in research of their application in smart self-sensing components. This study is focused on metakaolin geopolymer mortar doped with 0.05 and 0.10% carbon nanotubes, a conductive filler that effectively increases electrical conductivity without considerable deterioration of mechanical properties. Self-sensing performance of composites incorporated with electrodes and attached strain gauge was tested during different regimes of compressive loading cycles with continuous monitoring of strain and resistivity. Although the differences in sensitivity and repeatability were observed, all samples including the reference material have shown good response to applied loading.

Assessing the suitability of alkali-activated metakaolin geopolymer for thermochemical heat storage

This study investigates the suitability and potentials of using alkali-activated metakaolin geopolymers as sustainable low-cost thermochemical heat storage materials via water sorption and/or hydration reactions. Four different alkali-activated metakaolin geopolymer formulations were assessed. The cyclic water sorption capacity and moisture diffusion coefficients were assessed via two continuous water vapor sorption/desorption cycles using the dynamic water vapor sorption (DVS), proving the regeneration ability of geopolymers for sorption thermal energy storage. The thermochemical properties of geopolymers, including the dehydration enthalpy and activation energy, were determined. For the amorphous sodium aluminosilicate hydrate gel (N-A-S-H) with bulk Si/Al ratio of 1.5, the mass and volumetric energy storage capacity of 827.9 J/ghydrate sample and 350 kW h/m3 were achieved, with a charging temperature of around 120 °C. The outcomes of this study suggest that alkali-activated metakaolin geopolymers have the potential to be used for both low-temperature water sorption thermal energy storage and medium temperature hydration/dehydration thermochemical energy storage. The energy storage performances of metakaolin geopolymers are closely related to their aluminosilicate framework structures and surface textural properties. The partial crystallisation of the amorphous N(K)-A-S-H gel, resulting in the formation of micropores, which does not seem to affect the maximal water uptake but increases the proportion of the chemically bound water. The presence of the amorphous mesoporous aluminosilicate gel N(K)-A-S-H gel in geopolymers leads to desorption hysteresis at relative humidity higher than 30 %. Further optimisation of the synthesis approach, aluminosilicate framework structures, micro and mesopore structures will be required to optimise their overall thermal energy storage performances.

Effect of anisotropic pores on the material properties of metakaolin geopolymer composites incorporated with corrugated fiberboard and rubber

This paper compares the compressive strength and thermal conductivity of metakaolin geopolymer (MKG) incorporated with anisotropic and isotropic pores. MKG was prepared by activation with sodium hydroxide and sodium silicate. Corrugated fiberboard and rubber were included to create anisotropy of pores, and they were added in 3, 5, and 7 layers. Hydrogen peroxide and surfactant were added to generate isotropic pores. For geopolymer with corrugated fiberboard (MKG-C) and rubber (MKG-R), compressive test and thermal conductivity measurement were performed in perpendicular and parallel direction to the flat surface of fiberboard and rubber. The result showed that MKG-C and MKG-R exhibited mechanical and insulation anisotropically. The highest compressive strength was achieved in the parallel loading direction while the lowest thermal conductivity was attained in the perpendicular direction. MKG-C possessed better compressive strength of 26.9 MPa loaded in the parallel direction. The compressive strength performance of MKG-C was greater than MKG-R because of the fibrous-like structure, which further contributes to the strength. The thermal conductivity was low (0.15–0.20 W/mK) for both MKG-C and MKG-R. The anisotropy of pores led to high strength retention and improvement of thermal insulating properties. These properties were contrary to geopolymer with isotropic pores (MKG-F), which have excellent thermal insulating properties but low compressive strength to be eligible for structural applications.

Compressive strength and electrochemical impedance response of red mud-coal metakaolin geopolymer exposed to sulfuric acid

The performance of the geopolymer synthesized using red mud and coal metakaolin when exposed to sulfuric acid solutions was evaluated. The effects of different soaking times on mechanical properties, electrochemical properties, and microstructural changes to the materials were investigated. The degradation of the geopolymer was studied using corrosion depth and weight testing, uniaxial compression test, electrochemical impedance spectroscopy (EIS), nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), and scanning electron microscope-energy dispersive spectrometry (SEM-EDS). The EIS results indicate that the diameter of the impedance arc in the intermediate frequency region decreases with prolonged immersion. In addition, there was a significant correlation between the compressive strength and the impedance parameters (Rs and R1). Microstructural examination showed that the deterioration of the geopolymer observed was connected to depolymerization of the aluminosilicate polymers and destruction of microstructure in acidic media, which lead to loss of strength.

Conductive Metakaolin Geopolymer with Steel Microfibres​

Research of alkali-activated materials and geopolymers suggests their increased ability to transfer the electric charge thus indicating their suitability for self-sensing and other multifunctional composites. In this paper, the electrical properties of metakaolin geopolymer are enhanced by the incorporated steel microfibres that also improve the mechanical and fractural properties of the composite. Selected electrical properties of metakaolin geopolymer mortars with steel microfibres (up to 30 % of metakaolin wt.) were assessed via impedance spectroscopy analysis and followed by testing their compressive and flexural strength. Mercury intrusion porosimetry and SEM imaging enabled to characterize the binder microstructure and quality of fibre-matrix bonding.

The Effect of Red Mud Content on the Compressive Strength of Geopolymers under Different Curing Systems

To maximize the utilization of red mud in geopolymers, a red mud–metakaolin (RM-MK) geopolymer and red mud–fly ash (RM-FA) geopolymer were prepared, respectively. The effects of red mud content on the compressive strength and microstructure of the geopolymers were investigated under three different curing conditions. The results showed that the strength of the geopolymer decreased linearly with an increase in the red mud content, whether curing at room temperature or 80 °C. Surprisingly, curing in an autoclave, the appropriate amount of red mud had a favorable impact on the mechanical properties of the geopolymers. When the amount of red mud was 50%, the strength of the RM-MK geopolymer reached its highest compressive strength, 36.3 MPa, and the strength of the RM-FA geopolymer reached its highest at 31.7 MPa. Compared with curing at low temperature, curing the red mud-based geopolymers under a higher temperature and higher pressure can maximize the use of red mud. XRD analysis indicated that zeolite minerals formed. The SEM results showed that the geopolymers cured in an autoclave had a dense structure.

Thermal stability, pore structure and moisture adsorption property of phosphate acid-activated metakaolin geopolymer

Phosphate acid-activated metakaolin geopolymer (PMG) was successfully prepared using a two-step curing method and the thermal stability, pore structure and moisture adsorption property of the obtained PMG were studied by techniques of thermogravimetry (TG), mercury intrusion porosimetry (MIP) and dynamic vapor sorption meter (DVS). TG result shows that thermal decomposition of the PMG majorly occurs in the range of 220−550 ℃, much higher than that of the common binder of C-S-H, due to the removal of the chemically bonded water and the water content of the PMG is around 16%. MIP measurement indicates that the porosity of the PMG is 13.6% and the most probable pore size is about 100 nm. DVS results shows that the water adsorption amount of PMG powder is about 0.132 ml/g, which is in good agreement with the total porosity measured by MIP test.

Review on Mechanical Properties of Metakaolin Geopolymer Concrete by Inclusion of Steel Fibers

Review on Mechanical Properties of Metakaolin Geopolymer Concrete by Inclusion of Steel Fibers

Effect of Elevated Temperatures on The Performance of Metakaolin Geopolymer Pastes Incorporated by Cement Kiln Dust

Effect of Elevated Temperatures on The Performance of Metakaolin Geopolymer Pastes Incorporated by Cement Kiln Dust

Early age volume changes in metakaolin geopolymers: Insights from molecular simulations and experiments

The early age volume changes occurring during the geopolymerisation reaction are not sufficiently understood yet, due to shortage of experimental data and theoretical models. This work presents new results on chemical and autogenous deformation of sodium-activated geopolymers from metakaolin, focussing on the first 72 h of reaction. The results show that the geopolymers undergo early-age chemical expansion, not shrinkage. A model is proposed to explain the experimental result, leveraging recent advances from molecular simulations. The model predicts how the extent of chemical expansion is controlled by confined water in the molecular structure of the geopolymer. However, despite this underlying chemical expansion, geopolymer samples undergo autogenous shrinkage at the macroscale, which excludes self-desiccation as the origin of autogenous deformation. A better insight is gained by monitoring the kinetics of geopolymerisation using isothermal and differential calorimetry. Two kinetic regimes are identified, with apparent activation energies of approximately 90 kJ/mol and 70 kJ/mol. This suggests that two microscopic mechanisms concur to determine the early-age volume changes of geopolymer pastes.

Properties and reaction mechanism of phosphoric acid activated metakaolin geopolymer at varied curing temperatures

Reaction mechanism of phosphoric activated metakaolin is studied by techniques of calorimetry, ICP-OES, FTIR and NMR taking curing temperature and [H3PO4] as variables. A two-stage curing method including pre-curing at 40 °C for 24 h and second curing at 60/80 °C for another 24 h effectively mitigates thermal-cracking of the obtained silico-aluminate phosphate (SAP) samples, whose maximum compressive strength reaches 120 MPa. Dealumination of metakaolin in H3PO4 solution produces low aluminate-containing silicate units and subsequently condensation of silicate tetrahedrons occurs. Higher temperature and H3PO4 concentration accelerate the two processes. After complete reaction, AVI structure from metakaolin disappears and the dissolved Al preferably forms AlVI-O-P units. During reaction, metastable P-O-P intermediate appears in SAPs with higher P/Al ratio and finally transforms into Al-O-P structure upon PO43− consumption. Phosphate units as P(OAl)x(H2O)4-x are connected with Si or Al structure units. Major structural units of the SAPs include Al-O-P, Si-O-P, Si-O-Si, and Si-O-Al.

Effect of Elevated Temperatures on The Performance of Metakaolin Geopolymer Pastes Incorporated by Cement kiln dust

The aim of the present work was to study the influence of elevated temperatures on the thermal behavior of geopolymer cements based on the incorporation of metakaolin with cement kiln dust. Geopolymer composites were synthesized by partially substituted metakaolin (MK) with 0, 20, 30 and 40 wt% of cement kiln dust (CKD). The mixture of liquid sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as alkaline activator solution with fixed ratio 2.5 and the concentration of sodium hydroxide was 10 Molar. The obtained geopolymer specimens were cured in water at ambient temperature (25°C) for 28 days and then subjected to various elevated temperatures 200°C, 400°C, 600°C and 800°C for 1hour. Geopolymer cements were characterized before and after temperature exposure via visual appearance, X-ray diffraction (XRD), Fourier Transform infrared spectrometry (FTIR) and the compressive strength test. Some selected samples were investigated by using thermo gravimetric analysis (TGA/DTG).The results show that, all geopolymer specimens loss their compressive strength from ambient temperature to 400°C, this is due to the escape of moisture and dehydroxylation of aluminosilicate gel from the geopolymer matrix. However, geopolymer samples gained strength upon heating to 600°C as a result of further polymerization of unreacted silicate species. At 800°C, the geopolymer mix with 20% CKD retained highest strength and thermal stability than other mixes due to viscous sintering process which induced crack healing thus enhanced the mechanical properties of geopolymer under high temperature. This suggests that geopolymer paste that contains 80%MK and 20% CKD can withstand high temperature as well as very suitable for refractory and fire resistance applications.