Alkali-activated Aluminosilicate Research Articles

Studies on the performance of alkali-activated aluminosilicate geopolymer mortar against exposure to acid, sulfate, and elevated temperature

An alkali-activated aluminosilicate is a group of materials that have the potential to reduce the carbon footprint of the construction industry. Several combinations of materials have been explored for producing alkali-activated aluminosilicate geopolymer mortars, emphasizing the need to understand their resistance to chemical attack and elevated temperatures to ensure long-term durability. The present study prepared fly ash-based alkali-activated aluminosilicate mortar using fly ash (FA) and ground granulated blast furnace slag (GGBS) without heat curing. Properties such as compressive strength and weight loss were evaluated after chemical attack and exposure to high temperatures (200° to 1000°), and compared with PC mortars. The result shows that fly ash and GGBS-based alkali-activated aluminosilicate mortar (AAAM) exhibit better resistance to chemical attack and high temperatures than conventional mortar. Specifically, after 180 days of acid exposure, PCM showed a mass loss of 5.06% and compressive strength loss of 85%, while AAAM had a mass loss of 2.88% and compressive strength loss of 71%. Sulfate exposure led to a mass gain of 55.77% for PCM and 27.35% for AAAM, with compressive strength losses of 55.77% for PCM and 27.35% for AAAM. Elevated temperatures (1000°) resulted in a compressive strength loss of 68% for PCM and 45% for AAAM. To substantiate these results, X-ray diffraction (XRD) and Fourier Transformation Infrared Spectroscopy (FTIR) were used to study the changes in the bonding behavior of C-A-S-H (Calcium-Aluminate-Silicate-Hydrate) and N-A-S-H (Sodium-Aluminate-Silicate-Hydrate) when exposed to chemical attack and elevated temperatures.

Molecular dynamics simulation of the initial stage induction of alkali-activated aluminosilicate minerals.

With the increasing global concern over carbon emissions, geopolymers have garnered significant attention due to their energy-saving, waste utilization, and eco-friendly advantages. Metakaolin and slag, as aluminum-containing mineral materials in geopolymer production, have been widely studied and applied. Previous research has mainly focused on performance design and theoretical development, while the underlying mechanisms at the microscopic level remain unclear. In this study, we employed molecular dynamics simulations to investigate the microscale reaction behavior of geopolymers, exploring the induction process and structural evolution during the initial stages, and revealing the similarities and differences under alkali activation for different materials. Our findings indicate that the alkali activation process can be divided into two stages: mineral crystal deconstruction and oligomer polymerization. The role of NaOH differs between low-calcium and high-calcium systems, where in the low-calcium system, Na+ substitutes Ca2+ due to Ca2+ deficiency, participating in the formation of the network framework. Moreover, the high-calcium system exhibits a faster formation of the gel phase during alkali activation compared to the low-calcium system. This study provides valuable insights into the research and application of geopolymers.

Physical properties of alkali activated aluminosilicates based on low-reactivity ceramics in room temperature conditions

Alkali activated aluminosilicates (AAA), or geopolymers, are widely studied materials because they are supposed to become a more sustainable alternative to materials based on Portland cement, such is especially concrete. AAA materials are generally produced by activation of an aluminosilicate precursor by an alkaline solution – usually solution of sodium silicate and sodium hydroxide. The capability of the prepared material to be used as construction material is commonly evaluated by means of its compressive strength. The present paper aims to broaden the AAA materials characterization to other physical properties such are porosity and thermal conductivity, since these measures are closely related to the engineering performance of the material. The waste ceramic dust was used as precursor while the solution of potassium silicate was an activator. The relationships between the above listed physical properties and obviously on the material composition were searched.

Deterioration of basalt-based reinforcement in corrosive environments: experimental monitoring and mathematical models

The basalt-based reinforcing elements are considered as alternative to conventional steel-based reinforcing elements (rebars, wires). The motivation to use basalt-based elements (fibers, composite bars, meshes etc.) is better corrosion resistance of basalt fibers especially in sea-water environment, compared to carbon steel. Nevertheless, it does not mean that basalt fibers are 100% corrosion resistant. The basalt fibers are produced from silicate melt of proper composition, i.e. the basalt fibers are vulnerable to both acid and alkaline hydrolysis, as well as other silicates do. When basalt fibers are used as reinforcement in concrete, the alkaline hydrolysis will become an important issue. The present paper deals with experimental observation of basalt fibers in alkaline environment of Simulated Pore Solution. The fibers deterioration was monitored by their mass loss and SEM microscopy. Jander’s model was used to describe mathematically the kinetics of the fibers alkaline hydrolysis. The results revealed that a corrosion products layer is formed on the fibers surface in this environment. The composition of this layer corresponds to N-A-S-H and C-A-S-H phases known from alkali-activated aluminosilicates or hydrated Portland cement.

Optimising the Performance of CO2-Cured Alkali-Activated Aluminosilicate Industrial By-Products as Precursors

Three industrial aluminosilicate wastes were studied as precursors to produce alkali-activated concrete: (i) electric arc furnace slag, (ii) municipal solid waste incineration bottom ashes, and (iii) waste glass rejects. These were characterized via X-ray diffraction and fluorescence, laser particle size distribution, thermogravimetric, and Fourier-transform infrared analyses. Distinctive combinations of anhydrous sodium hydroxide and sodium silicate solution were tried by varying the Na2O/binder ratio (8%, 10%, 12%, 14%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5) to find the optimum solution for maximized mechanical performance. Specimens were produced and subjected to a three-step curing process: (1) 24 h thermal curing (70 °C), (2) followed by 21 days of dry curing in a climatic chamber (~21 °C, 65% RH), and (3) ending with a 7-day carbonation curing stage (5 ± 0.2% CO2; 65 ± 10% RH). Compressive and flexural strength tests were performed, to ascertain the mix with the best mechanical performance. The precursors showed reasonable bonding capabilities, thus suggesting some reactivity when alkali-activated due to the presence of amorphous phases. Mixes with slag and glass showed compressive strengths of almost 40 MPa. Most mixes required a higher Na2O/binder ratio for maximized performance, even though, contrary to expectations, the opposite was observed for the SiO2/Na2O ratio.

Application of diatomite as a substitute for fly ash in foamed geopolymers

In recent years, new climate targets in EU have led to a growing demand for construction materials with a lower carbon footprint. This implies a demand for research on materials with comparable properties and reduced CO2 emission to replace those currently in use. Geopolymers belong to the group of alkali-activated aluminosilicates, whose advantages include high compressive strength and high corrosion resistance. Examples of aluminosilicate materials used to produce geopolymers are fly ash, metakaolin or volcanic tuff. Recently, there have also been papers discussing the use of diatomite as a replacement for metakaolin in geopolymer materials. The purpose of this work is to investigate the use of diatomite as a fly ash replacement in the production of foamed geopolymers. For this purpose, fly ash based geopolymer samples with different amounts of diatomite (5%, 10%, 50%) were foamed using hydrogen peroxide as a foaming agent. Then, to observe the microstructure of the produced samples, they were subjected to scanning microscope observations. Compressive strength tests according to EN 12390-3 standard were carried out to check the strength properties after 30 days of curing. In addition, the thermal conductivity coefficients of the samples were investigated to better determine their potential industrial application. The expected result is a change in strength and thermal properties with increasing diatomite content.

Cracking Behaviour of Alkali-Activated Aluminosilicate Beams Reinforced with Glass and Basalt Fibre-Reinforced Polymer Bars under Cyclic Load

Cement is an essential material for concrete, which is mostly used worldwide second to the consumption of water. Due to the emission of CO2 into the atmosphere, the alternative material of geopolymer concrete was used. In this research work, silica and alumina content such as ground granulated blast furnace slag (GGBS), fly ash, and triggered by alkali activator solutions were used in geopolymer concrete. Due to the dwindling of river sand, alternative material of manufactured sand (M-Sand) was considered. To avoid corrosion problems in reinforced concrete structures, glass fibre reinforced polymer (GFRP) and basalt fibre-reinforced polymer (BFRP) bars were used as an alternative material for steel reinforcement in this work. As per the code, IS: 10262, the concrete mix design of M30 grade has arrived for the control mix and the same proportion was adopted for geopolymer concrete. Six beams of geopolymer and a concrete control beam of 100 × 160 × 1700 mm were cast and examined under a four-point cyclic load. Cyclic load results were compared with static load under ambient curing. Residual deflection, moment capacity, energy dissipation, and stress–strain behaviour results were compared and discussed. A sudden shear and premature failure were observed in FRP beams under static and cyclic bending tests.

Stabilization/Solidification of Wastes Containing Oxyanionic Metals: Reactions of Alkali-Activated Aluminosilicate Binders with Chromium, Arsenic, and Antimony in Comparison with Zinc

Stabilization/Solidification of Wastes Containing Oxyanionic Metals: Reactions of Alkali-Activated Aluminosilicate Binders with Chromium, Arsenic, and Antimony in Comparison with Zinc

Analysis of Displacement Measured during the Compressive Testing of Cylindrical Specimens

This paper deals with selected aspects of the analysis of the displacement and deformation stiffness of cylindrical specimens during compressive tests. A developed correction model is presented, and two types of material were selected for the adjustment of the correction model: concrete from an existing structure, and alkali-activated aluminosilicate composite. The correction model was calibrated using the test response of a steel cylinder.

Rheokinetic modeling of N-A-S–H gel formation related to alkali-activated aluminosilicate materials

Rheokinetic modeling of N-A-S–H gel formation related to alkali-activated aluminosilicate materials

Effect of Potassium Phosphate Content in Aluminosilicate Matrix on Mechanical Properties of Carbon Prepreg Composites.

Six matrices based on alkali-activated aluminosilicate with different amounts of potassium phosphate were prepared for the production of six-layer composite plates. The addition of potassium phosphate in the matrix was 2 wt%, 4 wt%, 6 wt%, 8 wt% and 10 wt% of its total weight. The matrix without the potassium phosphate was also prepared. The aim of this study was to determine whether this addition has an effect on the tensile strength or Young’s modulus of composites at temperatures up to 800 °C. Changes in the thickness and weight of the samples after this temperature were also monitored. Carbon plain weave fabric was chosen for the preparation of the composites. The results show that under normal conditions, the addition of potassium phosphate has no significant effect on the mechanical properties; the highest measured tensile strengths were around 350 MPa. However, at temperatures of 600 °C and 800 °C the addition of potassium phosphate had a positive effect, with the tensile strength of the composites being up to 300% higher than the composites without the addition. The highest measured values of composites after one hour at 600 °C were higher than 100 MPa and after 1 h at 800 °C higher than 85 MPa.

Effect of various amounts of aluminium oxy‐hydroxide coupled with thermal treatment on the performance of alkali‐activated metakaolin and volcanic scoria

This study aims to improve the stability of alkali-activated products, such as powdered volcanic scoria and metakaolin, by thermal treatment in addition to their partial replacement with aluminium oxy-hydroxide. To this effect, mixtures obtained from a partial replacement of aluminosilicate sources (volcanic scoria or metakaolin) with respectively 0, 10, 20 or 30 % of mass of aluminium oxy-hydroxide were alkali-activated and stored for 28 days at room temperature in the laboratory. The various specimens obtained were heated at 900–1200 °C and both the alkali-aluminosilicates and the heated products were analysed. It appeared that aluminium oxy-hydroxide improves the stability of heated products. Thus, without replacement, alkali-activated specimens of metakaolin showed cracks at 1100 °C while those of volcanic scoria melted at 1150 °C. Conversely, heated alkali-activated specimens of either volcanic scoria or metakaolin with the replacement showed stability up to 1200 °C and an improvement in the residual compressive strength as from 900 °C. Indeed, at 1150 °C, the metakaolin-based geopolymers or the alkali-activated volcanic scoria with 30 % of mass of the replacement showed residual compressive strength of 76.7 and 35.0 MPa, respectively, due to the sintering and to the formation of new crystalline phases (mullite, corundum, carnegieite and nepheline). Yet, residual compressive strength in the alkali-activated aluminosilicate specimens with replacement that were heated at 1200 °C dropped as a result of the partial dissolution of nepheline and carnegieite which may have generated closed pores within their microstructure. Hence, alkali-activation of volcanic scoria or metakaolin partially replaced with aluminium oxy-hydroxide is a remarkable process to get thermally stable products.

Structure-property relationships and state behavior of alkali-activated aluminosilicate gels

Structure-property relationships of alkali-activated aluminosilicate gels are studied using rheology, neutron scattering, solid-state NMR, and TEM to develop a pseudo-ternary state diagram. Empirical gel states are classified by the rheological behavior (sol-gel transition and scaling of storage modulus with aluminum concentration). The state boundaries are compared to alkali-activated materials from the literature including denser binders. This work focuses on two compositions of dilute gels, formulated to specifically quantify the effects of pH and aluminum concentration on gel microstructure and rheology. Gels formulated at constant pH of 12.5 show a change in morphology and silicon coordination, but consistent mass fractal dimension as aluminum concentration is increased. This microstructural behavior contrasts the characterization of gels previously formulated with a variable pH (range 3–11) which is dependent on aluminum concentration. These results inform the complicated interactions in the polycondensation reaction of alkali-activated binders and lead to a state diagram which unifies many structure-property observations reported for these materials.

Fracture Resistance of AAAS Composites with Ceramic Precursor

The paper deals with selected alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors in terms of their characterization by mechanical fracture parameters. Composites made of brick dust as a precursor and an alkaline activator with a silicate modulus of Ms = 0.8, 1.0, 1.2, 1.4 and 1.6 were investigated. The filler employed with one set of composites was quartz sand, while for the other set it was crushed brick. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were provided with notches at midspan of up to 1/3 of the height of the specimens after 28 days. 6 samples from each composite were tested. The specimens were subjected to three-point bending tests in which force vs. displacement (deflection at midspan) diagrams (F–d diagrams) and force vs. crack mouth opening (F–CMOD) diagrams were recorded. After the correction of these diagrams, static modulus of elasticity, effective fracture toughness, effective toughness and specific fracture energy values were determined using the Effective Crack Model and the Work-of-Fracture method. After the fracture experiments, informative compressive strength values were determined from one of the parts. All of the evaluations included the determination of arithmetic means and standard deviations. The silicate modulus values and type of filler of the AAAS composites significantly influenced their mechanical fracture parameters.

Strength of AAAS Composites with Ceramic Precursor over Time

The paper deals with the approximation of the time evolution of the strengths of selected alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors. Composites made of brick dust as a precursor and an alkaline activator with a silicate modulus of Ms = 0.8, 1.0, 1.2, 1.4, and 1.6 were investigated. The filler consisted of standard quartz sand in one case, and crushed brick in the other. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were tested in three-point bending after 7, 28, 90, and 300 days of maturation. From each composite, 3 specimens were tested and the compressive strength was determined from the 6 specimen parts that remained after the bending tests. The obtained flexural and compressive strength values for the abovementioned 4 composite ages were approximated by the exponential function , where the coefficient a represents a horizontal asymptote to the approximation curve, i.e. the theoretical strength of the composite at time t = ∞; the exponential term of the approximation with the coefficients b and c expresses the degree of the time-dependent change of the respective compressive strength in the interval t = (0, ∞). The approximation was performed with the least squares method using genetic algorithms implemented in the Java GA package with open source code.

Identification of AAAS Composites Mechanical Fracture Parameters

The paper deals with selected alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors in terms of characterization by mechanical fracture parameters. Two composites made of brick dust as a precursor and an alkaline activator with a silicate modulus Ms = 1.0 were investigated. The composites differed in the fineness of grinding of the precursor – in the first set it was 0 to 1 mm, in the second set 0 to 0.3 mm. The filler was crushed brick. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were provided with notches in the middle of the span up to 1/3 of the depth of the specimens after 28 days of hardening. Five to six specimens from each composite set were tested. The specimens were subjected to three-point bending tests, in which force vs. displacement (deflection in the middle of the span) diagrams (F–d diagrams) and force vs. crack mouth opening displacement (F–CMOD) diagrams were recorded. After correction of these diagrams, the values of static modulus of elasticity, effective fracture toughness, effective toughness and specific fracture energy were determined using the Effective Crack Model and the Work-of-Fracture method. After the fracture experiments, the values of informative compressive strength were determined on one of the fractured parts. At the same time, the values of static modulus of elasticity, tensile strength and specific fracture energy were identified using artificial neural networks and F–d diagrams measured and simulated in the ATENA FEM software. All evaluations included the determination of basic statistics of parameters.

Mechanical properties of fly ash-based geopolymer concrete with crumb rubber and steel fiber under ambient and sulfuric acid conditions

The fly ash-based geopolymer concrete is composed of alkali-activated aluminosilicate and aggregates. The removal of cement from concrete plays a significant role in reducing greenhouse gases. The industrial disposal of recycled tires is an environmental issue, and using them in concrete, while maintaining its mechanical properties and employing steel fiber to improve these properties, has received attention. Moreover, hydraulic structures, such as dams, piers, and canals, constitute a great portion of concrete structures in the world, and the mechanical properties of concrete in the acidic conditions of such environments should be evaluated. In previous studies, the geopolymer concrete with up to 20% of fly ash replaced with cement showed desirable results. In this research, the geopolymer concrete with up to 20% of fly ash replaced with cement, crumb rubber equal to an amount equal to 10% of the volume of fine grains, and steel fiber were made and then cured in dry conditions at the temperature of 60 °C. After 28 days, their mechanical properties were studied in the environment in contact with sulfuric acid. The results showed that the highest compressive and tensile strengths, being equal to 49 MPa and 4.7 MPa respectively, belonged to the geopolymer concrete containing crumb rubber and 1% fiber with 20% of fly ash replaced with cement. In contact with acid for 90 days, the concrete with 1% fiber and without cement had the highest compressive strength, equal to 34 MPa, showing the smallest reduction, equal to 26%. These results were evaluated with the analysis of the microstructure, along with XRF, ultrasonic, and XRD tests.

Soft Computing Techniques for the Prediction and Analysis of Compressive Strength of Alkali-Activated Alumino-Silicate Based Strain-Hardening Geopolymer Composites

A futuristic class of concrete that has ductile nature with zeroed cement and eco-friendly materials is popularly known as Engineered Geopolymer Composites (EGC). Research on strain-hardening geopolymer composites have started a decade back and there is an extensive opportunity for utilizing this kind of eco-material in the construction sector for sustainable development. The focus of this article is to develop predictive models for the compressive strength of EGC with the objective of assisting the experimental researches and to analyze the type of locally available eco-materials that could be adopted in developing the novel ductile geopolymer composites for structural applications. A database has been created with ten mix-design factors, including material contents and curing conditions as inputs. Three soft-computing tools viz., Artificial Neural Networks (ANN), Response Surface Methodology (RSM) and Gene-Expression Programming (GEP) have been exercised to create, train and validate the predictive models. Also, a critical comparative analysis has been performed. The accuracy of predictive models is tested with regression tools. Among these artificial intelligence tools, the RSM model has shown an accuracy level of 96% with the least RMSE of 2.8 and the ANN [10:8:1] model has shown 93% accuracy with RMSE 3.4. Only 80% accuracy has been shown for the GEP model with RMSE 6.2. The sensitive parameter in concrete composites is compressive strength where the prediction error should be minimum. This article concludes that the developed ANN and RSM models worked effectively in prediction whereas GEP is comparatively less accurate, which can be improved when influencing mix-design parameters are lesser.

Fracture parameters of alkali-activated aluminosilicate composites with ceramic precursor: durability aspects

Four sets of alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors were studied in terms of their characterization by mechanical fracture parameters as a basis for considerations of durability. AAAS composites made of brick powder as a precursor and alkaline activator with various silicate moduli (Ms = 0.8, 1.0, 1.2, 1.4, and 1.6) were investigated. The sets of AAAS composites differed in terms of the used filler: quartz sand or brick rubble. Two different precursor particle size ranges of 0–1 mm and 0–0.3 mm were used for both types of filler. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were provided with a notch at midspan after 28 days of hardening. The notches were cut up to 1/3 of the height of the specimens. The specimens were subjected to three-point bending fracture tests during which force vs. deflection (F–d) and force vs. crack mouth opening displacement (F–CMOD) diagrams were recorded. Tensile strength ft,ID and specific fracture energy GF,ID values were identified using the inverse method based on a neural network ensemble. The obtained F–CMOD diagrams were subsequently evaluated using the double-K fracture model supported by the ft,ID and GF,ID values. The double-K model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and unstable crack propagation.

Alkali-activated aluminosilicate sealing system for deep high-temperature well applications

This study proposes potential replacement for the Portland-based cement, which is a common sealant used in deep high-temperature geothermal wellbore completions. The experimental laboratory studies were focussed on alkali-activated aluminosilicates. It was proven, that the so-called, geopolymer-based sealing systems exhibit high compressive and flexural strength at elevated temperatures, good resistance towards thermal cyclic loading, high ductility, acid insensitivity, and improved water permeability. Additionally, alkali-activated aluminosilicate sealing systems are economically feasible and their CO2 emission, during the manufacturing process, is significantly lower in comparison with the conventional Portland-based cement types, making them an environmentally friendly option for deep wellbore completions in unconventional high-temperature geothermal systems.