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This study investigated the mechanical performance, toughness behavior, failure characteristics, and microstructure of geopolymer-stabilized laterites modified with modified natural rubber latex (MNRL) for application in pavement base and subbase layers. Class C fly ash was used as the primary binder, with MNRL added at a weight% of 0–10% of the dry soil. Unconfined compressive strength ( q u ), indirect tensile strength ( q t ), and flexural strength ( q f ) were evaluated, alongside brittleness index (BI), improvement toughness ratio (ITR), and scanning electron microscopy (SEM). The results showed that while the addition of MNRL reduced peak q u by 20–60%, most mixtures still satisfied subbase ( q u > 0.70 MPa) and base ( q u > 1.75 MPa) strength criteria. MNRL significantly decreased BI (from 1.00 to as low as 0.03) and increased ITR (up to 6.28), indicating a transition from brittle to ductile failure. SEM analysis confirmed the formation of elastic polymer films that bridge fly ash and soil particles, thereby enhancing matrix cohesion and reducing porosity. The optimal mixture containing 25–30% fly ash and 5–7% MNRL achieved q u values of 1.83–2.64 MPa with improved ductility. The findings confirmed that MNRL effectively enhanced toughness and fracture resistance, making it a promising sustainable additive for laterite stabilization in tropical pavement infrastructure.

The freeze-thaw damage of cementitious coarse grained fillings (CCGFs) significantly affects the firmness, stability, and durability of high-speed railway subgrades. It is favorable to employ geopolymer binders to improve the engineering performance of coarse grained fillings (CGFs), further ensure the safety of high-speed railway subgrades in cold regions due to their excellent mechanical and environmental-friendly performances. This study conducted a series of freeze-thaw and mechanical tests on geopolymer stabilized coarse grained fillings (GSCGFs). The influence of gradation, compaction degree, and freeze-thaw cycles on the integrity, strength, and stiffness of GSCGFs was investigated. The evolution law of their freeze-thaw damage was discussed quantitatively based on an improved damage factor. The results show that the mass loss rate of Group B GSCGFs with a fine-grained particle content of less than 15% was lower than that of Group A GSCGFs with a fine particle content between 15% and 30% overall. When other conditions remain unchanged, the mass loss rate of GSCGFs decreased with the increase of compaction degree but increased nonlinearly with the freeze-thaw cycles. The strength and stiffness of GSCGFs decrease nonlinearly with the freeze-thaw cycles and presented a first fast and then slow-down change trend, their stiffness evolution at different compaction degrees revealed a big difference due to the weakening bite effect and enhancing overhead structure among rock blocks. The strength reduction of Group A GSCGFs was less than that of Group B under the high compaction degree. The stiffness deterioration of Group A GSCGFs was about twice that of Group B. There seemed to be no absolute correlation that the strength of GSCGFs was positively correlated with their stiffness. By building an exponential relationship between the compressive strength of GSCGFs and the freeze-thaw cycles that followed the findings of previous several studies, an improved exponential damage evaluation model was proposed to represent the performance degradation of GSCGFs. The outcomes of this study can provide theoretical support for understanding the physical and mechanical behaviors of GSCGFs and applying them in engineering practices.

Soil stabilization is critical in civil infrastructure, acting as a cornerstone for sustainable and resilient building practices. It enables the construction of strong foundations capable of withstanding enormous loads and adverse conditions, assuring the safety and lifespan of structures such as buildings and roads. The utilization of industrial by products for enhancing the qualities of locally expanding soils has become increasingly popular, mostly due to its low carbon emissions and cost-effectiveness. The present investigation focused on the effect of the addition of Ground Granulated Blast furnace Slag (GGBS) and Geopolymer solution to expansive soil in order to reduce the erosion of slopes. Unconfined compressive strength tests were performed and found that 10% GGBS is the optimum amount for stabilization. SEM studies were conducted to know the microstructure before and after stabilization. The study determined that the rate of rainfall erosion on the stabilized slope was lower compared to the untreated soil, and the load-carrying capacity of the stabilized slope was much greater.

Organic soil is a problematic soil that needs to be treated before construction because of the low shear strength and high compressibility. Using by-product materials, such as fly ash (FA), to improve soils is a cost-effective and sustainable procedure. Because treatment with FA may lead to reduce shear strength, a FA-based geopolymer was used with a cohesive organic soil to substitute the reduction in strength. A series of unconfined compressive strength tests (UCS) were conducted on compacted specimens treated with FA and geopolymer. The geopolymer was produced by adding sodium hydroxide to activate the FA. Different levels of FA content, curing period, and temperature were applied to the specimens. The results indicate that for the FA treated specimens, the UCS decreased as the FA increased. For the geopolymer-treated specimens, as FA percentage in the geopolymer increased, the UCS increased and the axial strain at failure decreased. The optimum content of FA, in the geopolymer, was 20%, and the highest UCS was achieved at a curing period of 28 days at a temperature level of 65°C. Based on the obtained results, FA-based geopolymer can effectively be used to improve the strength of organic soils.

Geopolymers, or also known as alkali-activated binders, have recently emerged as a viable alternative to conventional binders (cement) for soil stabilization. Geopolymers employ alkaline activation of industrial waste to create cementitious products inside treated soils, increasing the clayey soils’ mechanical and physical qualities. This paper aims to review the utilization of fly ash and ground granulated blast furnace slag (GGBFS)-based geopolymers for soil stabilization by enhancing strength. Previous research only used one type of precursor: fly ash or GGBFS, but the strength value obtained did not meet the ASTM D 4609 (<0.8 Mpa) standard required for soil-stabilizing criteria of road construction applications. This current research focused on the combination of two types of precursors, which are fly ash and GGBFS. The findings of an unconfined compressive strength (UCS) test on stabilized soil samples were discussed. Finally, the paper concludes that GGBFS and fly-ash-based geo-polymers for soil stabilization techniques can be successfully used as a binder for soil stabilization. However, additional research is required to meet the requirement of ASTM D 4609 standard in road construction applications, particularly in subgrade layers.

In the current study, the durability of a clayey-sand stabilized with copper-slag (CS)-based geopolymer and alkaline activator solution (AAS) is investigated in freezing–thawing (F–T) cycles. For this purpose, tests including Atterberg limits, pH, standard Proctor compaction, unconfined compressive strength (UCS), accumulated loss of mass (ALM), swell and shrinkage, ultrasonic P-wave velocity, the toxicity characteristic leaching procedure (TCLP), and scanning electron microscopy (SEM) analysis were conducted. Various contents of CS (i.e., 0, 10%, and 15%) and 8 and 11 M NaOH were assessed in 0, 1, 3, 6, 9, and 12 cycles. The AAS contained 70% of Na2SiO3 and 30% of NaOH. Also, the weight ratio of CS to ASS was 1 (CS/ASS = 1). According to the TCLP test, the CS-based geopolymer stabilized samples have no environmental hazards. The results illustrated that the strength and stiffness of untreated soil increased with an increase in F–T cycles until cycle 3. For samples with 11 M NaOH concentration, loss of strength and stiffness were observed due to F–T cycles. Furthermore, the sample with 8 M NaOH showed hybrid behavior (i.e., an increase in strength and stiffness until cycle 3), similar to that of untreated soil, and then declined until cycle 9, similar to soil treated with 11 M NaOH. Based on the microstructural analysis, higher microcracks were observed in the 8 M sample compared with the 11 M sample due to soft-strain behavior. Furthermore, a higher microcrack formation resulted in a higher potential for swell mass and volume change.

This review provides a comprehensive analysis of the role of chemical agents in enhancing the performance of geopolymers for the stabilization and adsorption of heavy metals. Geopolymers, synthesized from aluminosilicate sources activated under alkaline conditions, are recognized for their versatile structural and environmental benefits, including low carbon emissions and high chemical resistance. Their unique Si-O-Al framework supports both stabilization/solidification (S/S) and adsorption processes, making them an ideal polymeric matrix for the immobilization of hazardous heavy metals in contaminated environments. The review categorizes the heavy metal immobilization mechanisms into physical encapsulation, ion exchange, hydroxide precipitation, and chemical complexation, depending on the specific metal species and geopolymer formulation. The introduction of chemical stabilizing agents, such as dithiocarbamate, sodium sulfide, and trimercaptotriazine, significantly improves the encapsulation efficacy of geopolymers by promoting targeted reactions and stable metal complexes. These agents enable the effective S/S of metals, such as lead, cadmium, and chromium, reducing their leachability and environmental impact. In addition to solid waste management applications, geopolymers have shown promising adsorption capabilities for aqueous contaminants, with chemical modifications further increasing their affinity for specific heavy metals. This review evaluates the impact of different agents and synthesis conditions on the overall performance of geopolymers in heavy metal immobilization, highlighting advances in environmental applications and future research directions for sustainable hazardous waste treatment.

Geopolymers, as a kind of inorganic polymer, possess excellent properties and have been broadly studied for the stabilization/solidification (S/S) of hazardous pollutants. Even though many reviews about geopolymers have been published, the summary of geopolymer-based S/S for various contaminants has not been well conducted. Therefore, the S/S of hazardous pollutants using geopolymers are comprehensively summarized in this review. Geopolymer-based S/S of typical cations, including Pb, Zn, Cd, Cs, Cu, Sr, Ni, etc., were involved and elucidated. The S/S mechanisms for cationic heavy metals were concluded, mainly including physical encapsulation, sorption, precipitation, and bonding with a silicate structure. In addition, compared to cationic ions, geopolymers have a poor immobilization ability on anions due to the repulsive effect between them, presenting a high leaching percentage. However, some anions, such as Se or As oxyanions, have been proved to exist in geopolymers through electrostatic interaction, which provides a direction to enhance the geopolymer-based S/S for anions. Besides, few reports about geopolymer-based S/S of organic pollutants have been published. Furthermore, the adsorbents of geopolymer-based composites designed and studied for the removal of hazardous pollutants from aqueous conditions are also briefly discussed. On the whole, this review will offer insights into geopolymer-based S/S technology. Furthermore, the challenges to geopolymer-based S/S technology outlined in this work are expected to be of direct relevance to the focus of future research.

It has always been a challenge for civil engineers to lay roads in the areas covered by expansive soil. The expansive soil undergoes extreme phase changes from being hard in hot summer to being slushy and without strength in monsoon season. Thus, the engineering properties of the expansive soil must be improved before laying the roads. This paper presents the results of experimental work carried out to improve the engineering properties of an expansive clay i.e. black cotton soil (BCS) by using fly ash geopolymer. Sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ) solutions were mixed in different ratios (0.5, 1, 1.5, and 2) and used for synthesizing the geopolymer. The stabilized BCS samples were characterized in the laboratory for various properties viz., Atterberg’s limits, free swell ratio, and unconfined compressive strength. The untreated and treated BCS samples were also analyzed for their microstructural and morphological properties by using the SEM (scanning electron microscope) images and the XRD (X-ray fiffractometer) and FTIR (Fourier-transform infrared spectroscopy) spectra. An increase in the unconfined compressive strength and reduction in free swell ratio as well as shrinkage limit was observed after stabilization with geopolymer. Results also indicate binding of soil particles and formation of dense microstructure resulting in higher strength and less swelling and shrinkage characteristics. Furthermore, the bender element test was used to indicate the improvement in stiffness of the geopolymer stabilized expansive soil in terms of shear wave velocity.

Soil stabilization using additives is considered as one of the sustainable alternative techniques to deal with acute material shortages. Critically reviewing the contemporary works on soil stabilization would help practitioners and researchers to comprehend the merits and demerits of each stabilization method, influential parameters, and associated constraints. Furthermore, the critical analysis might aid the authorities to develop standard protocols about the use of various additives for soil stabilization, which would persuade the industry personnel to adopt sustainable practices. This paper presents a methodical review of the present soil stabilization methods under five key areas namely, underlying chemistry, the influential factors, performance indicators, economic and environmental aspects, and industrial perspectives. Findings of the review indicate that cement-based stabilizers perform well irrespective of soil type and curing conditions, on the contrary, lime-based stabilizers require appropriate temperature and pH for strength development. The degree of stabilization depends mainly on soil type, compaction level, and curing type and condition. Most of the soils treated with different additives exhibited a reduction in plasticity index, and maximum dry density against stabilizer dosage irrespective of soil type. The typical values of unconfined compressive strength and California bearing ratio of inorganic and organic soils except for peat, treated with a 5% dosage of all common types of stabilizers, fall in between 700 and 1,500 kPa and 30–60%, respectively. Cement and cementitious blends exhibited better cost-to-strength, energy-to-strength, and CO 2 emission-to-strength ratios for soils with low plasticity whereas lime-blended stabilizers seemed effective for high-plastic soils.