Lime-activated ground granulated blast furnace slag (GGBS) is usually used to treat gypseous soils. However, sulphate-bearing soils often contain other sulphates, e.g., sodium sulphate (Na2SO4), potassium sulphate (K2SO4) and magnesium sulphate (MgSO4). Therefore, in this study, lime-GGBS was used as a curing agent for stabilising four sulphate-bearing soils, which were named as Na-soil, K-soil, Mg-soil, and Ca-soil. Unconfined compressive strength (UCS), swelling, X-ray diffraction, scanning electron microscopy and inductively coupled plasma spectroscopy tests, were conducted to explore the macro- and micro-properties of the lime-GGBS-stabilised soils. The results showed that at 5000 ppm sulphate, stabilised Mg-soil had the lowest swelling and highest UCS. At 20,000 ppm sulphate, stabilised Ca-soil had the lowest swelling, while stabilised Na-soil had the highest UCS. Generally, increasing sulphate concentration decreased swelling for Ca-soil but increased for other three soils, and decreased UCS for Mg-soil but increased for other three soils. This was because less ettringite was generated in the stabilised Ca-soil and the formation of magnesium silicate hydrate (MSH) in the stabilised Mg-soil. Therefore, the sulphate type had a significant impact on the swelling and strength properties of lime-GGBS-stabilised sulphate-bearing soil. It is essential to identify the sulphate type before stabilising the soil on-site.

In this study, ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as binders, while NaOH (NH) and Na2SiO3 (NS) served as alkali activators. Seawater (SW) was used instead of freshwater (FW) to develop a SW-GGBS-FA geopolymer for solidifying sandy soils. Geopolymer mortar specimens were tested for unconfined compressive strength (UCS) after being curing at room temperature. The results showed that the early strength of the seawater group specimens increased slowly less than that of the freshwater group specimens, while the late strength was 1.16 times higher than that of the freshwater group specimens. Factors including seawater salinity (SS), the GGBS/FA ratio, curing agent (CA) content, and the NH/ NS ratio were examined in this experiment. The results showed that the strength of the specimens was higher for SS of 1.2 %, G90:F10, CA content of 15 %, activator content was 15 %, and NH: NS of 50:50. The pore structure of the mortar specimens was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and computerized tomography (CT), revealing the mechanisms by which various factors influenced the microstructure. XRD indicated that SW-GGBS-FA geopolymer mortar newly produced Friedel salt and calcium silicate sulfate hydrate (C-S-S-H). The microstructures observed by CT and SEM showed that the pore radius of the seawater specimens was mainly less than 10 mu m, and the maximum crack length was 92.55 mu m. The pore radius of freshwater specimens was larger than that of seawater specimens, and the largest crack was 148.44 mu m, which confirmed that Friedel salt and C-S-S-H fill the pores and increase the UCS of the specimens.

Reactive magnesium oxide (MgO) and ground granulated blast furnace slag (GGBS) are cementitious materials introduced into sludge solidification, which not only reutilizes solid waste but also reduces cement consumption. Through the carbonation of reactive MgO and GGBS, the strength of the solidified sludge is further improved and CO2 is stably sequestrated in carbonate minerals. This paper investigates the strength and microstructural development and CO2 uptake of solidified sludge with varying water content, binder content, and ratio of MgO to GGBS. According to unconfined compressive strength (UCS) tests, when the binder content is 20% and the ratio of reactive MgO to GGBS is 2 & ratio;8, the strength of carbonated samples increases the most, which is six times that of the sample without reactive MgO. With binder content, the CO2 uptake of sample increases up to 2.1 g. Scanning electron microscope (SEM), X-ray diffractometer (XRD), and thermogravimetry-differential thermogravimetry analysis (TG-DTG) tests were conducted to systematically elucidate the micromechanism of carbonation of sludge solidified by reactive MgO and GGBS. Various carbonation and hydration products enhance the soil strength through filling pores and integrating fine particles into bulk aggregates. As the ratio of reactive MgO to GGBS increases, dypingite and hydromagnesite were converted into nesquehonite with better morphological integrity, and thus strengthens the soil skeleton. Diverse calcium carbonate polymorphs from carbonated GGBS also promote sludge strength growth and CO2 sequestration. Test results indicate that the addition of reactive MgO further improves the hydration and carbonation properties of GGBS, so the CO2 uptake grows with the ratio of reactive MgO to GGBS. The synergistic effect of reactive MgO and GGBS increases the carbonation performance of the mixed binder, so likewise the compressive strength.

This study investigates the potential application of a blend, termed GGRM, consisting of red mud (RM) and ground-granulated blast furnace slag (GGBS), for stabilizing subgrade expansive soil. RM, an industrial waste from aluminium refineries, poses environmental concerns due to its high alkalinity and presence of heavy metals. Despite its increased utilization in construction sector, research on its role in soil stabilization is limited. With this in mind, RM has been used as an activator for GGBS, to create synergy between these industrial wastes with an objective to utilize this blend for stabilization of black cotton soil (BCS). Therefore, laboratory investigations were conducted to assess the strength of BCS stabilized with GGRM comprising varying proportions of GGBS and RM (0:100, 70:30, 50:50, 30:70, and 100:0 by weight). Further, the optimal GGRM quantities were evaluated by mixing it in different proportions (5-30% by weight). This study also examined the effect of curing on strength properties and leaching behaviour and investigated the associated mechanisms through microstructural studies (XRD, XRF, SEM, and FTIR analysis). The leachate potential was assessed using ICP-OES analysis. Results indicated a maximum sevenfold improvement in unconfined compressive strength of BCS, from 131 to 920 kPa, after 28 days of curing in 70:30 combinations with 25% GGRM content. Furthermore, leaching of heavy metals from stabilized soils are within the permissible limits of hazardous waste management regulations. In conclusion, RM-activated GGBS blends emerged as a potentially sustainable binder, enhancing the strength of expansive soil for subgrade applications.

Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.

The purpose of this study was to evaluate the sustainability benefits of Class F fly ash (FA), lime sludge (LS), and ground granulated blast furnace slag (GGBS)-based geopolymer-stabilized Edgar plastic kaolin (EPK) clay using the sustainability index (ISus) approach. Geotechnical engineering operations usually precede most infrastructural projects, making pavement construction an integral contributor to various environmental effects, due to the production of enormous quantities of greenhouse gas emissions through soil stabilization activities. To nip these concerns in the bud, effective integration of these environmental implications must be achieved during the geotechnical planning phase. The life cycle assessment (LCA) method was used to assess a wide range of environmental effects of a project, from raw material procurement, manufacturing, transportation, construction, and maintenance to final disposal. It is a well-recognized tool for designing environmentally sustainable projects. Experimental results from the geopolymer-stabilized EPK clay showed a notable improvement in unconfined compressive strength of the geopolymer-stabilized clay with 15% (FA + LS) and 5% (FA + GGBS) contents of up to 697% and 464%, respectively, after 28 days of curing at elevated temperature, 70 degrees C. The sustainability index (ISus) of geopolymer and lime treatment methods was analyzed based on the concept of environmental, resource consumption, and socioeconomic concerns, which quantifies the sustainability through greenhouse gas emission, environmental impacts, and the cost of utilizing FA, LS, and GGBS in soil stabilization compared with traditional lime. LCA was conducted for traditional lime treatment, FA-LS, and FA-GGBS geopolymer-stabilized subgrades to determine the most sustainable treatment method. From the sustainability analysis, using FA, LS, and GGBS as geopolymer stabilizers for kaolin clay reduced the global warming potential by 98.03% and 77.55% over the traditional lime stabilizers at 8% dosage. More importantly, results from the sustainability index (ISus) computations showed that FA-LS (ISus = 12.88) and FA-GGBS (ISus = 29.72) geopolymer treatment methods of EPK clay subgrade soils are more sustainable alternatives compared to the traditional lime (ISus = 48.07) treatment method.

The efficiency of alkali-activated ground granulated blast furnace slag in stabilizing dredged sediments with high water contents is suboptimal because the activators become diluted. To improve stabilization efficiency, additives such as nano-CaCO3 are proposed. However, some of the proposed additives may not be practical owing to their high costs. This study experimentally investigates the addition of Na2CO3 for the stabilization of dredged sediment with high water contents (i.e., 100%) using Ca(OH)2-activated slag. Experimental results show the optimal content of Na2CO3 to obtain the highest 28-day unconfined compressive strength of stabilized sediments is 0.2% gravimetrically. Below the optimal content, the strength increases with Na2CO3 content. Above the optimal content, a decrease in strength is observed. By examining the reaction products and microstructure of the stabilized dredged sediments, it is observed that the coupling mechanism of cation exchange and calcite precipitation promotes the development of finer capillary pores, leading to a reduction in interpore connectivity and lower structural heterogeneity of the fine capillary pores. Experimental evidence from this study broadens the practical applications of sustainable soil stabilization using additives.

Red mud, a by-product generated during the extraction of aluminium from bauxite ore, poses challenges to the alumina industry due to its inherent sodicity, alkalinity and heavy metal content. Consequently, studies related to its bulk utilization and valorization have gained attention in the construction sector to promote sustainability. However, utilization of red mud in stabilization of expansive soils using alkali activation is seldom explored. Therefore, this study focuses on improving the geotechnical properties of an expansive soil (black cotton soil, BCS) through chemical stabilization by using blends of two distinct industrial wastes, viz. red mud and GGBS, termed as GGRM, activated with sodium hydroxide (NaOH) solution. The strength, stiffness and durability characteristics of these compacted blends were assessed based on a series of laboratory investigations like unconfined compressive strength, ultrasonic pulse velocity and wet-dry cycles tests. Leachate analysis was also performed to assess the geo-environmental issues of soil ameliorated with blends of alkali-activated GGRM blends. These blended specimens were moulded with different molar concentrations of NaOH solutions (i.e. 2, 5 and 10 M). Further, microstructural studies were carried out through XRD, SEM-EDS and FTIR analysis. The results show that heavy metal contents in alkali-activated specimens are within the permissible limits of USEPA guidelines. Based upon the assessments of strength, durability and P-wave velocity after 28 days of curing period, 25 and 30% binder contents of GGRM100:00, GGRM70:30 and GGRM50:50 corresponding to 5 M and 10 NaOH, were found suitable for subgrade applications in accordance with IRC 37 guidelines.

Effect of cement, Ground Granulated Blast Furnace Slag (GGBS), GGBS:magnesia (MgO) and GGBS:MgO:cement were studied as agents on stabilisation of a clay soil contaminated with glycerol solution. The contaminated soil was mixed with 5, 10 and 15% of the above agents. Atterberg limits and compaction tests were conducted on these mixtures. Additionally, strength and durability tests were performed on prepared samples at different curing times. The strength of soil contaminated with 4, 8, and 12% glycerol was reduced by 23.5, 30.1, and 36.5%, respectively, compared to the natural soil. By adding 5% cement to the soil contaminated with 4% glycerol, its strength after 7, 14, and 28 days of curing time was increased to 1581, 1984.5, and 2343.4 kPa, respectively. All the selected agents increased the strength of the contaminated soil and its increase was dependent on the percentage of the agent and curing time. It was revealed that GGBS:MgO:cement was more effective in increasing the strength than the other used agents. Durability tests also showed that the weight loss of the samples at different conditions was less than 10%. SEM results showed that the increase in strength of the soil results from the interaction between soil and agent.

The storage of mining waste not only consumes a vast tract of land, but it also poses environmental problems due to the leaching of heavy metals, dusting, and occasional slope failure. A coal mine overburden (hereafter referred to as black shale) is one of the mining wastes produced during the coal mining activity, dumping of which causes an environmental problem. By considering the issue associated with waste storage and the requirement for alternate civil engineering material, an attempt has been made to develop cementless controlled low strength material (CLSM) from black shale. For this purpose, black shale is mixed with a varying percentage of alkali activated ground granulated blast furnace slag (GGBS) and fly ash. The fresh CLSM is investigated for flowability, bleeding, and density, whereas the hardened CLSM is examined for unconfined compressive strength (UCS), hardened density, water absorption, ultrasonic pulse velocity, and durability. The CLSM developed in the present research is found to have self-flowing and self-leveling consistency, with flowability higher than 200 mm and a relative flow area between 2.06 and 7.70. The CLSM is found easily excavatable with a removability modulus less than 1. The 28-day UCS of CLSM is found between 0.48 MPa and 2.1 MPa, whereas it is found low to medium durable with a durability index between 84.44 % and 87.39 %. Further, the shear modulus of the hardened CLSM is evaluated using ultrasonic pule velocity. Finally, the CLSM is found non-toxic based on the result of the leaching analysis.