For construction quality control, the compaction delay referred to as mellowing time (MT) is crucial for achieving the desired outcomes of the chemical soil stabilization process in the field. In the current study, fly ash-based geopolymer (GFA) is used as a chemical stabilizer for expansive clay because of its significance in resource utilization and waste repurposing for soil stabilization through an enhanced process. The MT-influenced macroscopic physicomechanical properties and microstructural and mineralogical properties of expansive clay treated with varying GFA and curing period (CP) were investigated. The significant amelioration of strength and compression properties is observed through the unconfined compression test, California bearing ratio test, and one-dimensional (1D) consolidation test with an increase in GFA content and CP. This improvement is caused by the formation of cementitious [(N, C)-A-S-H] compounds as confirmed by SEM, EDAX, and XRD analyses. Meanwhile, as the MT increases, a decline in both the strength and compression characteristics of the GFA-treated specimens is observed. However, these specimens exhibit a reversal in deformability and brittleness with an increase in MT, which can be attributed to the development of a porous aggregated soil structure resulting from initial hydration before densification. In addition, a generalized mathematical modeling framework was established based on three-dimensional (3D) response surface modeling to quantify the MT-influenced strength and brittleness-related characteristics using MT, GFA, and CP as predictors. The established mathematical framework showed generality and reasonable accuracy in the prediction based on the experimental data. This article outlines the implications for practitioners and researchers of using GFA for the stabilization of expansive clay considering MT-influenced mechanical characteristics in the field.

The increasing global demand for metals, driven by technological progress and the energy transition, has led to an acceleration in the expansion of the mining and metallurgical industry, resulting in an increase in the generation of mine tailings. This waste, which is of heterogeneous composition and has high contaminant potential, represents significant environmental and social challenges, affecting soils, water, and the geotechnical stability of tailings. The accumulation of these mine tailings poses a problem not only in terms of quantity, but also in terms of physicochemical composition, which exacerbates their environmental impact due to the release of heavy metals, affecting ecosystems and nearby communities. This article reviews the potential of geopolymerization and 3D printing as a technological solution for the management of tailings, offering an effective alternative for their reuse as sustainable building materials. Alkaline activation of aluminosilicates facilitates the formation of N-A-S-H and C-A-S-H cementitious structures, thereby providing enhanced mechanical strength and chemical stability. Conversely, 3D printing optimizes structural design and minimizes material consumption, thereby aligning with the principles of a circular eco-economy and facilitating carbon footprint mitigation. The present study sets out to compare different types of tailings and their influence on geopolymer reactivity, workability, and mechanical performance. In order to achieve this, the study analyses factors such as the Si/Al ratio, rheology, and setting. In addition, the impact of alkaline activators, additives, and nanoparticles on the extrusion and interlaminar cohesion of 3D printed geopolymers is evaluated. These are key aspects of their industrial application. A bibliometric analysis was conducted, which revealed the growth of research in this field, highlighting advances in optimized formulations, encapsulation of hazardous waste, CO2 capture, and self-healing geopolymers. The analysis also identified technical and regulatory challenges to scalability, emphasizing the necessity to standardize methodologies and assess the life cycle of materials. The findings indicated that 3D printing with tailings-derived geopolymers is a viable alternative for sustainable construction, with applications in pavements, prefabricated elements, and materials resistant to extreme environments. This technology not only reduces mining waste but also promotes the circular economy and decarbonization in the construction industry.

This paper reports the influence of delay time on the index and engineering properties of geopolymer-, cement-, and lime-treated expansive soil. Locally available expansive soil was treated with different doses of slag-based geopolymer, cement, and lime. The index and engineering properties like Atterberg's limits, free swell index, grain-size distribution, compaction properties, and unconfined compressive strength (UCS) were evaluated at delay periods of 0, 6, 12, 24, 48, 72, and 168 h. Further, the mineralogical characteristics and microstructure of the stabilized materials were examined using X-ray diffraction (XRD) and scanning electron microscopic (SEM) images. It was observed that with an increase in delay time, the plasticity and swelling characteristics of the treated soil reduced with improvement in the soil grain size along with the formation of hydration and geopolymeric compounds. The delay in compaction results in the decline of the compacted density and UCS. The formation of hydrated products and flocs during the delay period caused loose packing under dynamic loading and affects the mechanical properties. A significant improvement in plasticity and engineering properties of the expansive soil was observed with geopolymer stabilizers. Thus, it is noteworthy to consider geopolymers as a new generation eco-friendly stabilizer for treating expansive clays for geotechnical constructions.