Metakaolin-based Geopolymer Mortars Research Articles

Towards Sustainable Material: Optimizing Geopolymer Mortar Formulations for 3D Printing: A Life Cycle Assessment Approach

Geopolymer-based concretes have been elaborated among others for their potential to lower the environmental impact of the construction sector. The rheology and workability of fresh geopolymers make them suitable for new applications such as 3D printing. In this paper, we aim to develop a potassium silicate- and metakaolin-based geopolymer mortar with sand and local earth additions suited for 3D printing and an environmental assessment framework for this material. The methodology aims at the optimization of both the granular skeleton and the geopolymer matrix for the development of a low-environmental-impact material suited for 3D printing. Using this approach, various metakaolin/earth geopolymer mortars are explored from a mechanical and environmental point of view. The environmental assessment of the lab-scale process shows an improvement for the climate change category but a degradation of other indicators, compared to Portland-cement-based concrete. Several promising options exist to further optimize the process and decrease its environmental impacts. This constitutes the main research perspective of this work.

Performance of Metakaolin-Based Geopolymer Incorporating Recycled Plastic Aggregate

Recently, research has been devoted to producing a more sustainable and environmentally friendly composite for substituting conventional cement concrete. This supports the global effort toward limiting the environmental impact of cement production. Geopolymer composites or alkali-activated materials have gained more attention within the research community due to the wide availability of waste (e.g., fly ash, slag) or natural (metakaolin, pozzolans) source materials suitable for geopolymer production. The present study investigates the potential of producing metakaolin-based geopolymer mortars with partial substitution of natural sand by recycled plastic fine aggregate (RPFA) to enhance composite sustainability. The primary variables of the experimental program include the percentage replacement of fine natural aggregate by RPFA (0, 10, 20, and 30% by volume). Tests comprising flowability, compressive strength, Flexural strength and unit weight of the various mixes were evaluated. The results indicated that replacing 10%, 20%, and 30% of sand with RPFA caused a reduction in the compressive strength by 10.6%, 21.8%, and 33.9% relative to the control mix. The flexural strength also decreased by 17.5%, 22.4%, and 30.4% compared to the control mix. Although substituting natural aggregate with RPFA reduced the mechanical properties, it improved the mix flowability by up to 20% relative to the control mix. Additionally, a reduction in the unit weight by up to 16.2% relative to the control mix was obtained, which offer a viable mean of producing lightweight mortar.

Influence of partial substitution of metakaolin by palm oil fuel ash and alumina waste ash on compressive strength and microstructure in metakaolin-based geopolymer mortar

Geopolymer is recognized as an alternate binder that compounds silica-rich and alumina-rich materials as raw materials and is produced by alkaline activation. In general, biomass ashes in particular for palm oil fuel ash (POFA) is an ideal starting material on the grounds of its high silica concentration, while industrial by-products, especially alumina waste (AW) is also employed as starting material due to its high alumina content. The objective of this research is to address the effects on the compressive strength and also the microstructure of metakaolin-based geopolymer mortar studied through the adaptability of the substitution of metakaolin (MK) by POFA and AW. In order to investigate the effects of POFA and AW substitution on the polymerization reaction and its outcomes, metakaolin-based geopolymers were produced. The most recent data suggests that POFA and AW probably serve as feedstocks for geopolymers with a little strength reduction. The partial substitution of MK by POFA reduces the polymerization reaction rate while maintaining the same water/binder ratio. However, because of the long-lasting polymerization reaction, it is still obtainable to reach a significant degree of polymerization reaction and also provides a comparable 28-day curing age compressive strength for 20 % replacement of MK by POFA. Considering 10 % substitution of POFA by AW, it results in 22.08 % improvement in the compressive strength after 28 curing days. On top of that, the compressive strength development of the geopolymer sample was investigated using scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). It was discovered that the density and the compressive strength were induced by the particle morphologies, the surface area of POFA and AW, and the chemical composition as a result of the geopolymerization.

An Investigation of the Strength Properties of Fly Ash and Metakaolin-Based Geopolymer Mortars Containing Multi-Wall Carbon Nanotube, Nano Silica, and Nano Zinc

In this study, the mechanical properties of geopolymer mortar composites containing different nanomaterials were investigated. Metakaolin (MK) and fly ash (FA) were used as binders in geopolymer mortar samples. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution (12 M) were used as alkali activators. Multi-walled carbon nanotube (MW-CNT), nano-SiO2 (NS), and nano-ZnO (NZ) were used in the study. Geopolymer mortar samples without nanomaterials were determined as control samples, and geopolymer mortar samples containing 0.5% by weight of MW-CNT, NS, and NZ were prepared. All prepared samples were cured at 20±2 °C laboratory conditions for 7 days and 28 days. The curing geopolymer mortar samples were carried out with compressive strength and flexural strength tests. As a result of this study, the mechanical strength of all geopolymer mortar samples containing nanomaterials increased compared to the control samples. The highest compressive strength and flexural strength were obtained from geopolymer mortar samples containing MW-CNT. These samples were followed by geopolymer mortar samples containing NS and NZ, respectively.

Impact of Sulfate in the Sand on the Compressive Strength of Metakaolin-Based Geopolymer Mortar

The advancement of cement alternatives in the construction materials industry is fundamental to sustainable development. Geopolymer is the optimal substitute for ordinary Portland cement, which produces 80% less CO2 emissions than ordinary Portland cement. Metakaolin was used as one of the raw materials in the geopolymerization process. This research examines the influence of three different percentages of sulfate (0.00038, 1.532, and 16.24) % in sand per molarity of NaOH on the compressive strength of metakaolin-based geopolymer mortar (MK-GPM). Samples were prepared with two different molarities (8M and 12M) and cured at room temperature. The best compressive strength value (56.98MPa) was recorded with 12M with lower sulfate content (0.00038%) at 28 days. Also, an inverse relationship is recorded between the increasing sulfate percentages in the sand and the compressive strength values of (MK-GPM). A higher reduction in the compressive strength results at 28 days (60.88% per 8M/NaOH) and (62.23% per 12M/NaOH) was associated with a higher percentage of SO3 in the sand (16.24%).

Effect of ground concrete waste as green binder on the micro-macro properties of eco-friendly metakaolin-based geopolymer mortar

Upcycling of ground concrete waste powder as green binder is an effective and high-value approach to reducing concrete waste. This study utilized ground concrete waste powder including recycled paste powder and recycled concrete powder for sustainable metakaolin-based geopolymer mortar. Concrete waste powder with irregular particle shape mainly contains hydration products, quartz and calcite. Substituting concrete waste powder for metakaolin reduces the number of alkali-activated cementitious products in blended geopolymer paste, but the nucleation and filling effects of concrete waste powder can improve paste micro-structure. Incorporating concrete waste powder raises the drying shrinkage of geopolymer mortar; recycled paste powder blended geopolymer mortar has higher drying shrinkage than recycled concrete powder blended geopolymer mortar, and the maximum drying shrinkage of geopolymer mortar with 75% recycled paste powder is 178.7% higher than that of geopolymer mortar with 75% recycled concrete powder. The compressive strength first rises and then declines with the rise of concrete waste powder content. Recycled paste powder blended geopolymer mortar has better compressive strength than recycled concrete powder blended geopolymer mortar, and the 28-d compressive strength of geopolymer mortar with 75% recycled paste powder is 34.4% larger than that of geopolymer mortar with 75% recycled concrete powder. Substituting concrete waste powder for metakaolin up to 75% declines the water and chloride ingress in blended geopolymer mortar, and recycled paste powder blended geopolymer mortar has lower water absorption and chloride migration than recycled concrete powder blended geopolymer mortar. Optimizing concrete waste powder type and content can prepare sustainable metakaolin-based geopolymer mortar having superior strength and low transport property.

Effect of calcium carbide residue on the sulphate resistance of metakaolin-based geopolymer mortars

Sulphate resistance is an essential indicator for assessing the durability of geopolymer mortars. This study investigates the effects of calcium carbide residue (CCR) addition on the sulphate resistance of metakaolin-based geopolymer mortar via strength tests. The influence of NaOH concentration and NaOH/Na2SiO3 mass ratios on the compressive strengths was investigated. The prepared geopolymer mortars, with and without CCR, were cured at room temperature, and their durability was evaluated in a 5 % magnesium sulphate solution. The durability of the optimum geopolymer mix was compared with Ordinary Portland Cement mortar. The results indicated that the optimum 7-day compressive strength for geopolymers with and without CCR was achieved at 10 M NaOH with a NaOH/Na2SiO3 mass ratio of 1:2. The addition of CCR resulted in an increase in compressive strength by 26.12 % compared to the geopolymer without CCR. The sulphate resistance of geopolymer material with CCR was lower than those without CCR but higher than OPC-based mortar, which recorded a reduction in strength of about 3.2 % after sulphate exposure. The findings indicate that CCR addition to metakaolin-based geopolymer can produce high compressive strength with enhanced sulphate resistance compared to the OPC.

Impact of Sulfate in the Sand on the Absorption and Density of Metakaolin-Based Geopolymer Mortar

Impact of Sulfate in the Sand on the Absorption and Density of Metakaolin-Based Geopolymer Mortar

Effects of Different Kinds of Defoamer on Properties of Geopolymer Mortar

As a new type of green inorganic material, geopolymers have excellent mechanical properties, durability, and less environmental pollution. It is considered a new building material that can replace cement, but it also has some disadvantages such as high viscosity, poor fluidity, and more apparent pores after hardening. In this study, the uniaxial compressive strength test of geopolymer mortar was carried out, and the effects of alkali equivalent, alkali activator modulus, bone glue ratio, and silica fume content on the mechanical properties of geopolymer mortar were analyzed. The test results show that when the alkali equivalent is 13%, the alkali activator modulus is 1.4, the bone glue ratio is 2.0, the silicon powder content is 8%, and the metakaolin-based geopolymer mortar has higher uniaxial compressive strength. Through the comparative test of adding different kinds of defoamers and dosage, the effect of defoamers on the compressive strength, fluidity, density, and water-absorption of geopolymer mortar was further studied. The fluidity, density, and water-absorption were improved, and the uniaxial compressive strength was reduced. The formation of cementitious material in the mortar was confirmed by scanning electron microscope (SEM) observation. It was found that the pore structure and pore distribution changed with the content of different defoaming agents, and the microstructure of mortar after defoaming agent material treatment was shown. The proportion and distribution of Na, Al, and Si atoms were analyzed by energy dispersive spectroscopy (EDS). This experimental study shows that the defoamer can be an effective additive for geopolymer mortar.

Influence of rice husk ash substitution on some physical, mechanical and durability properties of the metakaolin-based geopolymer mortar

In this study, it is aimed to investigate the influence of rice husk ash, which is a waste by-product of industrial production, on ultrasonic pulse velocity, compressive strength, flexural strength and high temperature endurance of the metakaolin-based geopolymer mortar. For this, the sand was substituted by rice husk ash (RHA) at the rate of 25%, 50% and 75% by wt. in the production of geopolymer mortar. A total of 4 series of metakaolin-based geopolymer mortars (reference series and three series with RHA substitution) were produced. In this study, the geopolymer, in other words, the binder of the mortar was produced by metakaolin and ground granulated blast furnace slag reacting with the mixture of sodium hydroxide (12M NaOH) and sodium silicate (Na2SiO3) solutions. The ratio of metakaolin and reactant mixture (12M NaOH + Na2SiO3) was determined for each series following the preliminary experiments. On the specimens produced as 50 mm cube and 40 x 40 x 160 mm prism, the intended experiments were carried out after specimens underwent curing in a dry oven at 60oC during 72 h and gained strength. The results showed that RHA could be used as a filling material in metakaolin-based geopolymer mortars, and metakaolin-based geopolymer mortars with 50% RHA substitution can be an alternative to the pure metakaolin-based mortar.

Metakaolin based geopolymer mortar as concrete repairs: Bond strength and degradation when subjected to aggressive environments

By harnessing the benefits of lowering cost and reducing CO2 emission, employing geopolymer as the repair materials have been gaining interest. This article investigated the bond strength and degradation of metakaolin-based geopolymer mortar subjected to rapid efflorescence exposure, acid attack, freeze-thaw cycles, wet-dry cycles, and heat-cool cycles. The slant shear strength tests evaluated the new-old mortar bond strength. FTIR, XRD, and TGA were conducted to monitor the deterioration of geopolymers. Visual observation and ICP-OES tests were performed to quantify the efflorescence risk. Results showed that acid exposure mainly reduces bond strength by degrading the geopolymer framework. In aggressive environments involving moisture and temperature changes, i.e., freeze-thaw, wet-dry and heat-cool cycles, geopolymers exhibit negligible deterioration. However, the shrinkage induced by water migration and the volume expansion caused by elevated temperatures significantly decrease (up to 90%) the bond strength of geopolymer repair mortar. The negative effect imposed by the efflorescence should not be neglected. A significant bond strength reduction (up to 20%) was observed for geopolymer repair mortar suffering from efflorescence. Samples with higher granulated blast furnace slag (GGBS) addition show lower strength loss, benefiting from their lower efflorescence extent. Stoichiometrically designing the geopolymer repair binder to avoid efflorescence is recommended.

Valorization of queen scallop shells in the preparation of metakaolin-based geopolymer mortars

This paper aims to assess the effect of the seashell waste (SW) incorporation on the performance of MK-based geopolymer mortar. The SW powder was introduced as partial replacement of MK with a substitution rate of 0, 10, 20 and 30%. Its effect on setting time, water porosity, mechanical strengths and both drying and autogenous shrinkage was investigated. A special attention was also devoted to the evaluation of the efflorescence stability. The obtained results show that partial replacement of MK by SW powder leads to limit considerably the water demand of the binder resulting in mortars with higher mechanical strengths and lower porosity and shrinkage. In addition, SW powder allows to accelerate the setting time of geopolymer mortars. The autogenous shrinkage was found to increase with increasing SW percentage. However, the total shrinkage was dominated by the drying shrinkage that represents around 85% of the total strain at 90 days regardless the SW replacement rate. In terms of efflorescence stability, the lowest efflorescence formation was attributed to the geopolymer mixture formulated with 30% of SW powder.

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.

Physical and mechanical properties of metakaolin-based geopolymer mortars containing various waste powders

In this paper, it was aimed to evaluate the effectiveness of four different types of filler materials with particle sizes below 63 μm in sustainable geopolymer mortars. For this purpose, 25%, 50%, and 75% limestone powder (LSP), basalt powder (BP), waste marble powder (WMP), and recycled aggregate powder (RAP) were substituted with river sand and 13 different mixtures including reference were obtained. Metakaolin was used as the main binder material, and sodium hydroxide/sodium silicate was used in a ratio of 1:2 as an activator. In addition, blast furnace slag was added to the mixture as a reaction accelerator at a rate of 13% of the amount of metakaolin. To determine the mechanical properties of the produced geopolymer mortars, compressive strength, flexural strength, splitting strength, porosity, ultrasonic pulse velocity (UPV), and abrasion tests were performed. Also, SEM and XRD analyses were performed to examine the microstructures of the specimens. The satisfactory results obtained proved that all four types of filler materials can be used in metakaolin-based geopolymer mortars. Optimum rates for limestone powder, basalt powder, waste marble powder, and recycled aggregate powder were obtained as 50%, 50%, 25%, and 25%, respectively.

Mechanical performance of metakaolin-based geopolymer mortar blended with multi-walled carbon nanotubes

In recent decades, the cement industry has been viewed as a major environmental problem mainly due to carbon dioxide CO2 emissions during the production of Portland Cement (PC). Among the solutions to this problem is to replace Portland cement-based materials with alkali-activated materials. Metakaolin-based geopolymer mortars are currently considered a serious alternative to ordinary Portland cement mortar due to its various advantages. The present experimental study aims to develop metakaolin-based geopolymer mortars reinforced with multi-walled carbon nanotubes (MWCNTs). The content of MWCNTs incorporated was 0.1; 0.2; 0.3, and 0.4 wt%, respectively, with respect to the mass of metakaolin. A mixture without the addition of carbon nanotubes was also prepared and used as a reference (control sample). The alkaline activation of metakaolin was carried out using aqueous sodium silicate solution having a molar ratio (SiO2/Na2O) equal to 1.77. Mechanical characterization of the hardened samples was performed after curing for 3, 7 and 28 days. The results indicate that the incorporation of multi-walled carbon nanotubes in the geopolymer matrices improves compressive strength. Microscopic analysis has shown that these carbon nanotubes contribute to the densification of the geopolymer matrix and give rise to crack bridging mechanisms. The highest value of the compressive strength was recorded using an alkali silicate content equal to 8 (expressed as a percentage of Na2O) combined with 0.2% of multi-walled carbon nanotubes in the geopolymer mortar. The integral absolute error (IAE) calculated on the compressive strength values at different curing ages are all within an acceptable range (0–10%).

Impact of Ca+ content and curing condition on durability performance of metakaolin-based geopolymer mortars

To overcome massive pollution and energy consumption resulting from cement production in addition to concrete’s durability problems, geopolymer concretes (GPC) and mortars (GPM) are recently gaining increasing interest. GPCs are manufactured based on different ingredients such as Fly Ash, GGBS, and other Alumina-Silicate rich materials and polymerized by using alkali activator. However, based on the major polymeric constituent material and curing condition, the properties of GPC are determined. In Egypt, metakaolin (MK) is available in several locations, which after calcination exhibits satisfactory pozzolanic activity. MK is a good replacement of cements in concrete and GPC as it consumes less fuel and produces much lower pollutants. In this research, the durability of MK mixes, that can be utilized in normal construction locations are investigated. Metakaolin based geopolymer mortars (MK-GPM) with up to 60% OPC are made to investigate the effect of OPC inclusion on durability related characteristics. The influence of curing conditions at ambient temperature (23 ± 2 °C) as well as at 60 °C heat curing is also investigated. Water transport properties are evaluated. Durability related characteristics in terms of change in weight and compressive strength with time after exposure for 10 weeks to chemical solution (10% MgSO4, H2SO4 (pH=3) and 10% NaCl). Furthermore, microstructure properties are investigated through X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) to identify the phase and chemical composition. The results reveal that, heat curing of MK-GPM reduces its sorptivity by 9 ± 2% and water absorption by 13 ± 3%. On the other hand, the inclusion of OPC in MK-GPM (by more than 5%) increases water absorption and sorptivity and consequently reduces durability. Although, MK-GPM shows better durability when exposed to aggressive environmental attacks, incorporating cement up to 20% demonstrates better durability performance than OPC mortar. The study of the microstructure of tested mixes explains and confirms the experimental results.

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%.

Relative Performance of Limestone, Marble, and Basalt Powders in Replacement of a Recycled Fine Aggregate from Red Mud and Metakaolin-Based Geopolymer Mortar

Relative Performance of Limestone, Marble, and Basalt Powders in Replacement of a Recycled Fine Aggregate from Red Mud and Metakaolin-Based Geopolymer Mortar

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.

Behavior of Metakaolin-Based geopolymer concrete at ambient and elevated temperatures

Geopolymer or alkali-activated binders are emerging as a potential green sustainable alternative for ordinary Portland cement (OPC). In addition to the environmental benefits of geopolymers, it possesses excellent mechanical properties, including good resistance to elevated temperatures. Although many studies were conducted on the thermal performance of metakaolin-based geopolymer mortar and pastes, the performance of metakaolin-based geopolymer concrete under elevated temperature has been rarely studied. Therefore, the present study investigates the behavior of MK-based geopolymer concrete under ambient and elevated temperatures of 200 °C, 400 °C, and 600 °C. The experimental program of this study comprised five mixes with different formulations to primarily investigate the influence of varying Na2O/Al2O3 and SiO2/Al2O3 molar ratios. The results are discussed in terms of the visual observations for the fresh and hardened specimens, compressive strength development, stress–strain behavior, splitting tensile strength, water absorption, and weight loss percentage due to exposure to elevated temperatures. The residual compressive strength varied from 56% to 63%, 38% to 51% and 28% to 34% after exposure to 200 °C, 400 °C, and 600 °C, respectively. The rate of degradation in the modulus of elasticity with the increase in the exposure temperature is much higher than the compressive strength. Models are proposed for predicting the residual compressive strength and modulus of elasticity of geopolymer concrete after exposure to elevated temperature, which show good correlations with experiments. The SEM-EDS analysis confirms the formation of dense homogeneous geopolymerization gel and corroborate the trends of strength degradation after exposure to elevated temperature.