Alkaline Activator Research Articles

Alkali activation of blast furnace slag using Bayer red mud as an alternative activator to prepare cemented paste backfill

Alkali-activated materials (AAMs) are increasingly used in mine backfilling as substitutes for Ordinary Portland Cement (OPC) due to their superior performance and environmental advantages. However, the high cost of commercially available alkaline activators such as sodium hydroxide and sodium silicate limit the widespread use of AAMs. This study investigates the use of Bayer red mud (RM) as an alternative activator to sodium hydroxide (SH), with blast furnace slag (BFS) as the precursor. Cemented paste backfill (CPB) was prepared by replacing 75% of OPC with these AAMs, combined with tailings and water. The results showed that CPB made with AAMs exhibited significantly better mechanical properties, with a 57% to 94% increase in uniaxial compressive strength (UCS) at 28 days compared to CPB made with OPC. Even with an RM-to-SH ratio of 2:1, UCS improved by 3% over SH-only samples. Analysis of hydration products and microstructure revealed that RM provides more alkaline ions, enhancing the formation of calcium-alumino-silicate-hydrate (C-A-S-H) and effectively filling capillary pores. This study demonstrates a cost-effective, environmentally friendly approach for producing AAMs, highlighting RM's potential as a sustainable alternative to commercial activators for CPB applications.

Alkaline activation via in-situ caustification of one-part binders of composite precursors of waste glass and limestone

Mixtures of powders of waste glass (WG), limestone (LS), Na2CO3 and CaO were used to formulate novel one-part in situ alkali-activated cement (WG-AAC). The in-situ interaction Na2CO3-CaO-H2O promoted the formation of CaCO3 and NaOH, which promoted the WG and LS dissolution and influenced the micro- and molecular features of the resulting cementitious products. Pastes and mortars developed 1-year strengths of up to 29 MPa and were stable underwater. Characterization by XRD, SEM, EDS, and 29Si-NMR indicated that a Na2CO3:CaO ratio close to 1:1 resulted in polymerized C-S-H, CaCO3, silica gel, and Ca-modified silica gel, which were intimately intermixed and possibly crosslinked through Q3 bonds. Such phases interacted synergistically improving the underwater stability of the WG-AAC, indicating that in-situ caustification is a suitable and practical alkaline activation for SiO2-rich precursors.

Enhancing Mechanical Strength and Microstructural Properties of Alkali-Activated Systems through Nano Graphene Oxide Dispersion and Polycarboxylate Ether Admixture

The dispersion of graphene oxide (GO) nanoparticles in alkali-activated concrete with / without superplasticizers can help in understanding the effect it has on its mechanical strength and microstructural properties. The dispersion of GO in alkali activator fluid of 10(M) and 12(M) with / without polycarboxylate ether (PCE) admixture has been explored in this study. The alkali activator solution of 10(M) NaOH solution with PCE shows better dispersion than 12(M) NaOH solution, as higher alkalinity leads to agglomeration of GO. The study investigated the effect of incorporating PCE in GO-based alkali-activated slag (AAS) mortar with 8(M), 10(M) and 12(M) of alkaline activator solution. The mechanical strength and microstructural characteristics of conventional AAS (without both GO and PCE), GO-based AAS (without PCE) and GO-based AAS with PCE of the respective molar concentration of activator fluid are analysed. The mechanical strength of the AAS mortars has been evaluated using compressive, flexural, and splitting tensile strength testing. The micro-structural and mineralogical characteristics of the binders are evaluated using Field Emission Scanning Electron Microscopy (FESEM with EDS), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The addition of only GO (0.06% of binder w/w) and the addition of both GO and PCE in AAS have shown up to 30% and 40% mechanical strength improvement with respect to conventional AAS, respectively. The effectiveness of PCE and percentages of strength improvement are higher with a lower molarity of activator fluid, and vice versa. Adding GO and PCE to the AAS system improves its hydration rate and denser microstructure, enhancing its strength.

Tensile strength and durability performances-based evaluation of 3D-printed and mold-cast fibrous geopolymer composites produced at various alkaline activator combinations

This study aimed to investigate the effects of the sodium silicate-to-sodium hydroxide ratio, SH molarity, and carbon fiber volume fraction on the tensile strength and durability properties of mold-cast and 3D-printed geopolymer composites, including flexural and splitting tensile strengths, ultrasonic pulse velocity, water absorption, sorptivity index, and chloride penetration properties. For that purpose, the ground-granulated blast furnace slag and fly ash were employed as alumino-silicate-rich raw material. In order to activate the alumino-silicate-rich raw material, two sodium silicate/sodium hydroxide ratios of 1 and 2 and three sodium hydroxide molarities of 8M, 10M, and 12M were designated. Furthermore, carbon fiber was incorporated into the geopolymer composites at three volume fractions: 0%, 0.3%, and 0.6%. In total, 18 nonfibrous and fibrous geopolymer composites were manufactured in two different ways: mold-cast and 3D-printed. The findings demonstrated that the strength and durability characteristics of 3D-printed specimens were inferior to those of mold-cast specimens, attributed to the presence of weak interfacial bonds between layers. It has been observed that the incorporation of carbon fiber has the effect of improving tensile strength performance. Nevertheless, the addition of carbon fiber led to a slight decrease in UPV values, and an increase in water absorption and sorptivity index values. Also, it adversely influenced the chloride penetration of geopolymer composites. The findings of the study also indicated that increasing the sodium hydroxide molarity had a positive impact on the strength and durability properties of the composites. Nevertheless, it was observed that increasing the sodium silicate-to-sodium hydroxide ratio led to a decrease in both tensile strength and durability performances. Additionally, the microstructure of the geopolymer composites was analyzed using scanning electron microscope (SEM) images.

Thermal behavior of construction and demolition waste-based geopolymer

Unsorted Construction and Demolition Waste (CDW) from residential building was tested as solid precursor for obtaining eco-sustainable alkali activated materials with potential applications in the building industry. Suitable reactive systems for material consolidation were tested, including alkaline solutions of sodium hydroxides and/or silicates at different concentrations. Metakaolin (MK) was also tested as an additional precursor together with CDW in different ratios to optimize geopolymerization. An MK/CDW weight ratio of 40/60 and sodium silicate as alkaline activator allowed the production of a well-reacted and cohesive material, with a bulk density of 1.35 g/cm3, a monomodal mesoporosity with a modal pore size of 0.0214 µm (open porosity ∼42 vol%), and a compressive strength of 25 MPa, thus showing similar features to those of pure metakaolin based-geopolymers. Thermal characterization was performed up to 1000°C showing that the material can exhibit thermal stability up to 650°C. Above that temperature a shrinkage due to viscous flow occurred, followed by an expansion over 750°C with the formation of macropores and dense struts. Based on these results, the developed CDW-based geopolymer has the potential for use in green building applications, with adequate thermal stability up to medium-high temperatures.

Development and performance evaluation of ultra-lightweight geopolymer foam insulation material

The preparation technology for new ultra-lightweight geopolymer insulation materials (ULGIM) has been developed based on the principle of alkaline activation, and ULGIM for building walls have been obtained. It has improved the problem of traditional inorganic foam insulation material that cannot balance density, insulation performance, mechanical performance and environmental performance. The composition of supplementary cementitious materials, the mass ratio between each component, and water to binder ratio (w/b) were used to analyze the thermal conductivity, dry density, volumetric water absorption, compressive strength, average pore diameter, and porosity of ULGIM. The life cycle assessment (LCA) method was employed to assess the environmental impact of ULGIM production. The test results showed that ULGIM achieved a dry density and thermal conductivity of ULGIM only 181.17 kg/m3 and 0.0427 W/(m·K), respectively, and the optimal compressive strength was 0.72 MPa at 7 d. ULGIM exhibited superior compressive strength, lower thermal conductivity, and smaller environmental impact in comparison to cement-based foamed materials with comparable dry density.

Performance evaluation and mix design of ambient-cured fly ash-phosphogypsum blended geopolymer paste and mortar

A practical mix design and performance metrics for fly ash-phosphogypsum blended geopolymer paste and mortar is lacking. This study focused on investigating the physico-chemo-mechanical performance and mix design of ambient-cured fly ash-phosphogypsum geopolymer paste (FPGP) and mortar (FPGM). The geopolymer was formed by reacting binary powder precursor (fly ash+phosphogypsum) and alkaline activator (NaOH+Na2SiO3). The fly ash was substituted with varying weight proportions of phosphogypsum (i.e., 10 %, 20 %, 30 %, 40 %, 50 %). Experimental testing and analysis were done based on ASTM standards, XRF, XRD, SEM-EDS, ANOVA, and Python. The workability, setting time, flexural strength, compressive strength, morphology, and mineralogy were studied. The multivariate regression approach was used to model the relationship between compressive strength and alkaline liquid/precursor. The optimum mixture conditions for FPGP and FPGM were 30 wt% phosphogypsum, alkaline liquid/precursor of 0.4, 10 M NaOH, Na2SiO3/NaOH of 1.5, and binder/aggregate of 1.0. The results showed that the workability of FPGP ranged from 185 mm to 112 mm while that of FPGM ranged from 145 mm to 100 mm. The FPGP and FPGM had considerably lower initial and final setting times of (18 – 37 min, 81 – 155 min) and (14 – 29 min, 67 – 142 min), respectively. The compressive strength of FPGP ranged from 7.3 MPa to 27.24 MPa while that of FPGM ranged from 9.5 MPa to 43.27 MPa. There was a strong connection between compressive and flexural strength giving R2 values > 0.8. Based on the adjusted R2 values and ANOVA, the proposed mix design models were statistically significant since the p-value (0.000) was less than the 0.05 significance level and the value of F (197.953) was greater than the critical value of 1. At high curing duration, the concentration of NaOH and alkaline liquid/precursor facilitated the dissolution of Ca2+ in phosphogypsum and Si4+and Al3+ in fly ash forming a C-(N)-A-S-H matrix crucial to the strength development of geopolymers. The statistical metrics implied a good performance accuracy and reliability of the proposed model equations and can find practical applications in construction materials design. For optimal results, it is recommended to use the prediction models within the specific input parameters employed in this study.

Artificial intelligence prediction of the mechanical properties of banana peel-ash and bagasse blended geopolymer concrete

This research explores the application of Artificial Intelligence (AI) techniques to assess the mechanical properties of geopolymer concrete made from a blend of Banana Peel-Ash (BPA) and Sugarcane Bagasse Ash (SCBA), using a sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) ratio ranging from 1.5 to 3. Utilizing three AI methodologies—Artificial Neural Networks (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Gene Expression Programming (GEP)—the study aims to enhance prediction accuracy for the mechanical properties of geopolymer concrete based on 104 datasets. By optimizing mix designs through varying proportions of BPA and SCBA, alkaline activator molarity, and aggregate-to-binder ratios, the research identified combinations that significantly enhance mechanical properties, demonstrating notable international relevance as it contributes to global efforts in sustainable construction by effectively utilizing industrial by-products. The experimental results demonstrated that increasing the molarity of the alkaline activator from 4 to 10 M significantly enhanced both the compressive and flexural strengths of the geopolymer concrete. Specifically, a mixture containing 52.5% SCBA and 47.5% BPA at a 10 M molarity achieved a maximum compressive strength of 33.17 MPa after 20 h of curing. In contrast, a mixture composed of 95% SCBA and 5% BPA at a 4 M molarity exhibited a substantially lower compressive strength of only 21.27 MPa. Additionally, the highest recorded flexural strength of 9.95 MPa (77.25% SCBA and 22.5 BPA) was observed at the 10 M molarity, while the flexural strength at 4 M was lowest, at 4.12 MPa (95% SCBA and 5% BPA). Microstructural analysis through Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (ED-SEM) revealed insights into the pore structure and elemental composition of the concrete, while Thermogravimetric Analysis (TGA) provided data on the material’s thermal stability and decomposition characteristics. Performance analysis of the AI models showed that the ANN model had an average MSE of 1.338, RMSE of 1.157, MAE of 3.104, and R2 of 0.989, while the ANFIS model outperformed with an MSE of 0.345, RMSE of 0.587, MAE of 1.409, and R2 of 0.998. The GEP model demonstrated an MSE of 1.233, RMSE of 1.110, MAE of 1.828, and R2 of 0.992, confirming that ANFIS is the most accurate model for predicting the mechanical and rheological properties of geopolymer concrete. This study highlights the potential of integrating AI with experimental data to optimize the formulation and performance of geopolymer concrete, advancing sustainable construction practices by effectively utilizing industrial by-products.

The Effect of the Ratio of Fly Ash to Alkaline Activator and the Molarity of NaOH on the Mechanical Properties of Fly Ash-Based Aggregates

The global demand for aggregates has escalated, leading to a decline in the availability of quality natural aggregates. In response, the cold bond pelletization (CBP) process emerged in the early 2000s as a novel approach to artificial aggregate production, utilizing dry powdered fly ash. This method involves agglomerating fly ash particles at room temperature in an inclined rotating pan to form pellets. However, the abstract lacks clarity in elucidating the significance of this approach. Our study investigates the mechanical properties of aggregates produced through the CBP method via experimental laboratory methods, focusing on variations in the ratio of fly ash to alkaline activator (FA/AA) and the molarity of Sodium Hydroxide (NaOH). Notably, we found that an effective molarity of 15 resulted in the lowest Aggregate Impact Value (AIV) percentage, indicating improved mechanical properties. Furthermore, we observed fluctuations in AIV values across different FA/AA ratios and NaOH molarities, suggesting nuanced effects on aggregate quality. Our findings underscore the importance of optimizing parameters in the CBP process for enhanced aggregate performance.

Clayey soil stabilisation with geopolymerized olivine and glass fibers

In some engineering applications soil stiffness only could not be a reliable parameter in accordance with specific standardizations especially when dealing with dynamic loading. In other words, foundation soil should be altered regarding its ductility in order to prevent sudden damage due to brittleness. Plenty of researchers were concerned to focus on soil reinforcement using glass fibers. Besides, the alkaline activation method has been adapted to alter the strength properties of soft soil. Furthermore, recent alkaline activation of soft soil, using olivine and Potassium hydroxide, coupled with soil reinforcement was adapted to change the post-peak behavior of soft soil. The aim was towards ultimate strength increase and enhancement of failure mode. In this research, geopolymerized soil and geopolymerized reinforced soil were cured for 7, 28, 90 and 180 days respectively. Compressive stress tests were conducted on both mixtures namely SO and SOG samples. Results drawn from the tests revealed a drastic increase in compressive strength for SO samples cured for 28 and 90 days, namely 3,64 MPa and 7,5 MPa respectively. Though a sharp drop was seen when approaching failure. With the addition of reinforcing glass fibers for the suggested curing regimes the failure mode was enhanced to become more ductile.

Study on Impact Resistance of Alkali-Activated Slag Cementitious Material with Steel Fiber

Alkali-activated slag cementitious materials (AASCMs) use alkaline activators to activate blast furnace slag and waste slag to replace traditional Portland cement, which can reduce CO2 emissions. An impact resistance test and scanning electron microscopy (SEM) microscopic performance analysis of alkali-activated slag cementitious material specimens with four different steel-fiber contents are performed. The effects of steel-fiber volume content and strain rate on the dynamic elastic modulus Ed, dynamic compressive strength σd, dynamic peak compressive strain εc, and energy absorption of the AASCM-SS are studied. The results indicate that the dynamic elastic modulus Ed, dynamic compressive strength σd, and energy absorption of the AASCM-SS increase with the increase of strain rate, and the dynamic peak compressive strain εc decreases with the increase of strain rate. The dynamic elastic modulus Ed, dynamic compressive strength σd, and dynamic peak compressive strain εc of the SS-AASCM increase first and then decrease with the increase of steel-fiber content. When the steel-fiber content is 0.5%, the σd and εc of the AASCM-SS are the highest, increased by 9.9% and 19.3%. The energy absorption of AASCM-SS increases with the increase of steel-fiber content. A dynamic constitutive model of the FR-AASCM considering the influence of damage, strain rate, and steel-fiber volume fraction is established. The proposed constitutive model is in acceptable agreement with the experimental AASCM-SS dynamic stress–strain curve, and the correlation coefficient is 0.91.

Assessing the Influence of Calcium-Based Alkaline Activators and Metakaolin on the Compressive Strength Development of Geopolymer Concrete for Different Mix Design Parameters

Assessing the Influence of Calcium-Based Alkaline Activators and Metakaolin on the Compressive Strength Development of Geopolymer Concrete for Different Mix Design Parameters

Review of Recent Developments in Tensile Properties of Engineered Geopolymer Composites

Engineered Cementitious Composite (ECC) is a type of highly ductile cementitious material. However, due to its characteristics of high energy consumption and high carbon emissions, it is necessary to seek a new type of low-carbon and environmentally friendly substitute. Engineered Geopolymer Composite (EGC), as a promising construction material for replacing ECC, has broad application prospects. Through visual analysis of the relevant literature in Web of Science, it was discovered that the research on EGC mainly concentrates on aspects such as the types of precursors, the chemical composition of the alkali-activated solution, and the related parameters of fibers. This paper mainly combines the relevant experimental research data on the tensile properties of EGC conducted by scholars at home and abroad, and focuses on analyzing the influence of precursor types, the chemical composition of the alkaline activator, and fibers on the tensile properties of EGC. The statistical results indicate that fly ash and ground granulated blast-furnace slag (GGBFS) are the most commonly used precursor materials. Replacing an appropriate amount of fly ash in the precursor with GGBFS can significantly enhance the tensile strength of EGC. The type of alkaline activator and its molarity have a relatively obvious influence on the tensile properties of EGC. An increase in the molarity of NaOH within a certain range can enhance the tensile strength of EGC. Furthermore, the incorporation of fibers, especially synthetic fibers such as polypropylene (PP) and polyvinyl alcohol (PVA) fibers, as well as inorganic fibers such as glass fibers (GF) and carbon fibers (CF), can effectively enhance the tensile strength and tensile strain capacity of EGC. The use of hybrid fibers may further improve the tensile properties.

Synthesis and Characterization of an Alkali-Activated Binder from Blast Furnace Slag and Marble Waste

This study reports an alkali-activated binder including blast furnace slag (BFS) together with marble waste (MW). Cement is an industrial product that emits a significant amount of CO2 during its production and incurs high energy costs. MW is generated during the extraction, cutting, and processing of marble in production facilities, where dust mixes with water to form a settling sludge. This sludge is an environmentally harmful waste that must be disposed of in accordance with legal regulations. In this study, a substantial amount of MW, a by-product with considerable environmental and economic impacts worldwide, was utilized in the production of a binder through the alkaline activation of BFS. In doing this, different experimental parameters were tested to obtain the best binder samples according to workability and mechanical properties. Then, some experiments such as drying shrinkage determination, strength testing, and microstructure analyses were fulfilled through samples with the best values. The findings supported the improvement of the rapid-setting property of BFS by means of the addition of MW. MW reduced the time-dependent drying shrinkage values of BFS by 55%, especially in slag alkaline activation systems with a low or moderate alkali activator content. The substitution of MW (≤50%) in BFS increased flexural and compressive strengths (4.5 and 61.7 MPa), while a reference sample contained BFS only. Although the use of MW did not create a new phase, it contributed to a C-S-H bonding structure during the alkali activation of BFS in a microstructure analysis.

Concretes meeting the requirements of sustainable construction

The article concerns the production of lightweight geopolymer concretes based on raw materials from alkali-activated waste, which is consistent with the doctrine of sustainable construction. Fly ash, which is the main component of these geopolymer composites, constitutes energy waste and causes lower emissions of greenhouse gases and other pollutants than traditional cement. The article presents the optimisation of the geopolymer concrete recipe with different dosages of fly ash (200, 300, 400, 500, 600 and 700 kg/m3) and two recipes, the first of which is based on the use of fly ash aggregate, the largest fraction of which was subjected to surface impregnation, and the second one is based on the use of aggregate without any impregnation. Both recipes use an alkaline solution for alkaline activation with a concentration of 6 mol/dm3. Compressive strength tests and apparent density were carried out on the samples. The adequacy of the use of surface impregnation has been demonstrated in the case of low fly ash content (<500 kg/m3), and the optimal recipe based on fly ash in the amount of 600 kg/m3 was indicated.

Silicomanganese fume-based alkali-activated mortar: experimental, statistical, and environmental impact studies.

This paper evaluates the flowability and strength properties of alkali-activated mortar produced using silicomanganese fume (SiMnF) as the sole binder, combined with alkaline activators and sand, cured at room temperature (23 ± 1 °C). A total of 18 mixes were prepared by varying binder content (370, 470, and 570 kg/m3), alkaline activator content (33, 43, and 53% of binder by weight), and NaOH concentration (8 M and 12 M). The SiMnF-based alkali-activated pastes were characterized using SEM, XRD, and FTIR techniques to study morphology, mineral composition, and functional groups, respectively. Statistical modeling, including analysis of variance (ANOVA) and response surface method (RSM), was performed to optimize the mixes, and a life cycle assessment was conducted to evaluate the environmental impact of the developed SiMnF-based alkali-activated mortars (SiMnF-AAM). The experimental results showed that an optimal mix design with 470kg/m3 SiMnF, 43% alkaline activator content, and NaOH concentrations of 8M and 12M achieved the best balance of flow and strength. XRD and FTIR analyses confirmed that Nchwaningite was the primary reaction product, with secondary phases including magnetite, manganese ferrite, and potassium feldspar, influenced by alkali concentration. The SiMnF-based mixtures had a significantly lower CO₂ footprint (0.08kg CO₂/kg) compared to the cement-based mix, with alkali activators being the primary contributors to emissions. The developed SiMnF-AAM mixes, cured at room temperature, exhibited improved workability, mechanical properties, and reduced environmental impact, making them adaptive to real-life applications.

Design of a novel ternary blended Self-Compacting Ultra-high-performance Geopolymer Concrete

In this research study, the Taguchi orthogonal array (TOA) optimisation method was used to design the optimum mixture proportions of ternary blended Self-Compacting Ultra-High-Performance Geopolymer Concrete (SCUHPGC). The SCUHPGC mixtures, cured at ambient conditions, included Ground Granulated Blast Furnace Slag (GGBFS), Fly Ash (FA), and Silica Fume (SF) as aluminosilicate sources and sodium hydroxide solution and sodium silicate solution as alkaline activators. The effects of six factors at three levels on the compressive strength of SCUHPGC were investigated. The considered factors were the binder content, the ratio of fly ash to ground granulated blast furnace slag (FA/GGBFS), the ratio of silica fume to binder content (SF/Binder content), the ratio of alkaline activator to binder content (AAL/Binder content), the ratio of sodium silicate to sodium hydroxide (SS/SH), and the concentration of sodium hydroxide solution. Twenty-seven SCUHPGC mixtures were evaluated. The slump flow diameter of the optimum SCHUPGC was 740 mm, which satisfies the requirements of self-compacting concrete. The maximum 28-day compressive strength of 132.7 MPa was achieved by the optimum SCUHPGC mixture, which contained a binder content of 1050 kg/m3, a FA/GGBFS ratio of 0.3, an SF/Binder content ratio of 0.05, an AAL/Binder content ratio of 0.4, a SS/SH ratio of 4.0, and an SH concentration of 12 M. The 28-day flexural strength and tensile strength of the optimum SCUHPGC mixture were 9.6 MPa and 4.9 MPa, respectively.

Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)2 for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF2), [AlF6]3-, and [FeF6]3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

Study on the rheological properties and compressive strength mechanism of geopolymer cementitious materials for solid waste

The large-scale storage of industrial solid waste can cause serious environmental pollution issues. Utilizing industrial solid waste to produce green cementitious materials is an effective alternative to cement. This study utilizes steel slag (SS) and calcium carbide residue (CCR) as alkaline activators, combining them with blast furnace slag (BFS) and fly ash (FA) to create SCBF cementitious materials. Investigate the flowability, setting time, rheological properties, compressive strength, pore structure, and microscopic morphology of SCBF cementitious materials under different conditions and conduct molecular dynamics simulations. The research findings indicate that with an increase in BFS content, the flow performance of SCBF decreases, setting time shortens, plastic viscosity and yield stress gradually increase, UCS increases, and the proportion of harmful pores inside the samples decreases. When SS:CCR:BFS:FA is at a ratio of 25:25:30:20, with an increase in curing temperature, the UCS of samples shows a trend of first increasing and then decreasing. The proportion of harmful pores follows a pattern of initial decrease followed by an increase. When the curing temperature is 30 °C, the proportion of harmful pores is 0.31 %, reaching a local minimum, and the UCS strength reaches 13.83 MPa. In the raw materials, SiO2 and Al2O3 aggregate with Ca2+ in an alkaline environment to form C-(A)-S-H three-dimensional network gel. The potential energy, kinetic energy, non-bonding energy, and total energy of Tobermorite 14 Å crystals gradually increase with higher curing temperatures, with the most intense molecular motion occurring at 60 °C. The research findings are beneficial for promoting the use of industrial solid waste to manufacture green cementitious materials as substitutes for cement-based materials. They also provide a theoretical basis for the industrial application of high-temperature-cured solid waste cementitious materials.

Applying Alkali Activator and Hydrophobic Agents in Clay-Based Mortars for Enhanced Properties

Clay-based mortars are susceptible to water intake and exhibit low mechanical strength, presenting challenges in their application within the construction sector. This research addresses these vulnerabilities by investigating the combination of alkali activators with waterproofing agents, specifically a nano-clay and an acrylic emulsion, to enhance the properties of clay mortars. Alkali-activated materials are known for their superior mechanical properties and sustainable potential, especially when derived from low-cost by-products. Recent studies have focused on alkali activation using clays and soils as precursors to improve their physical and mechanical properties while increasing durability. However, the high absorbency of these mortars remains a concern, as it can lead to matrix degradation. Therefore, to address these problems, this research studied the combination of a highly alkaline activator (potassium metasilicate) with hydrophobic agents, such as a nano-clay and an acrylic emulsion, using two different clayey soils. The results indicated that potassium metasilicate (PO) enhanced the mechanical properties and stability for both aluminosilicate systems, while nano-clay (PONC) significantly reduced the capillary absorption through time, especially in A2 systems. The addition of acrylic emulsion (POD) proved highly effective in both systems, significantly improving durability. By integrating these agents, the mortar systems were protected against water intake, while durable construction materials were formed.