To achieve environmental and economic goals in ground improvement, a one-part geopolymer (OPG), synthesized from binary precursors (fly ash [FA] and granulated blast furnace slag [GGBFS]) and a solid activator (solid sodium silicate [NS]), was used to replace ordinary Portland cement (OPC) for stabilizing high-water-content soft clay. The effects of different initial water content (50%, 80%, 100%, and 120%) and various OPG binder content (10%, 20%, 30%, and 40%) on the strength development of the OPG-stabilized soft clay were investigated through unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial tests. Additionally, the microstructure evolution and the distribution of pores in the OPG-stabilized soft clay were examined by the utilization of mercury intrusion porosimetry (MIP) and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) techniques, respectively. The life cycle assessment (LCA) methodology was then used to analyze the environmental and economic advantages of employing an OPG binder for soil stabilization. It was revealed that the optimal content of OPG binder was contingent upon the water content of soft clay, with variations in requirements for strength development. Specifically, for soft clay not demanding early strength, a maximum binder content of 20% is proposed. Conversely, for soft clay that necessitated rapid strength gain, the OPG binder content escalated with increasing water content of the soft clay, in which soft clays with different water contents had corresponding required amounts of OPG binder. For soil with water content ranging from 50% to 80%, the recommended OPG binder content is 20%. While for soil with 100% and 120% water content, the designed OPG binder content is suggested to be 30% and 40%, respectively. The environmental assessment demonstrated that the utilization of OPG as a binder for the stabilization of soft clay reduces costs and carbon emissions in comparison to OPC. The present study provides substantial theoretical validation for the utilization of OPG as a novel binder to stabilize soft clay with elevated water content, which holds promise as an eco-friendly and cost-effective solution in ground improvement.

Clays often have unfavorable geotechnical properties that limit construction applications on them. There is a need for sustainable soil improvement techniques to enhance the strength and stiffness of clays. While previous studies have explored clay stabilization with common supplements like cement, lime and fly ash, the utilization of sludge pond ash (SPA) as a sustainable additive has been limited and there is a lack of understanding of the interactive effects of SPA proportion, moisture content, and curing time on the mechanical behavior of clay. The objective of this study is to examine the mechanical properties of clay enhanced with SPA under different curing conditions. To achieve this, different proportions of SPA were mixed with the clay to obtain accurate findings on the efficacy of SPA addition on compaction and unconfined compressive strength (UCS) of the clay to determine mechanical properties. Scanning electron microscopy (SEM) provided imaging of clay improved with SPA to evaluate the microstructural changes in soil texture. Firstly, the sludge from a pond burned at 1000 degrees C (the optimal temperature determined by microstructural X-ray diffraction (XRD) analysis) was added to the mixture as 0, 2, 4, 6, 8 and 10% of the soil's dry weight, respectively. The studied samples were prepared with the same energy (equivalent to the standard Proctor test) at different moisture contents and were tested in a uniaxial device at 7, 28 and 56 days of curing. It was found that adding SPA to the base soil decreased the maximum dry unit weight (MDUW). On the other hand, it increased the optimum moisture content (OMC) of the compacted mixture. The study examined the combined effects of moisture content and curing time on the compounds, revealing that these factors induced a decrease and an increase in the UCS, respectively. The addition of SPA as an additive material to the clay mixture was found to exert a significant effect on the strength properties of the clay, with an optimal percentage of around 10%. Empirical correlations were also developed to predict the UCS of the SPA-improved clay with high precision. Furthermore, SEM analyses show that SPA acts as a glue gel between aggregate in the mixture and coat clay particles that changes the blend texture and alters weak bonding to aggregate-like particles. The results of both macro-and micro-scale analyses collectively confirm the superior efficacy of the optimal SPA replacement in enhancing various strength and stiffness properties of the clay.