Long-term performance of pavement sections depends on the structural integrity and strength of its individual layers. Clay-rich soils do not often meet the structural requirements needed to perform as an effective subgrade material. Among the different in situ techniques available to enhance the engineering properties of these clay-rich soils, lime stabilisation is the most preferred alternative. Although lime treatment improves the strength properties of clay-rich soils due to sustained pozzolanic reactions, the intrusion of external water can deter the benefits of stabilisation processes. The objective of this study was to identify the possible causes of strength and durability loss in lime stabilised subgrade soil during moisture exposure and determine the effect of curing period on the extent of moisture-induced damage incurred. Reasons for immediate strength loss observed in stabilised materials when exposed to moisture conditions were also investigated as part of the study. Thermal analysis techniques, such as differential scanning calorimetry, differential thermal analysis and thermo-gravimetric analysis were used in identifying and quantifying the calcium silicate hydrate (C–S–H) phases precipitating in lime-treated soils and also to determine the water retention properties of these cementitious materials. Results suggest the inherent affinity and water holding capacity of the precipitated C–S–H phases are partially responsible for the deterioration in strength properties observed in stabilised layers exposed to water, especially during early curing periods. As curing proceeds, the increased suction potential created by the C–S–H phases is counteracted by a higher matrix strength. This phenomenon causes a reduction in external water movement and associated strength loss in stabilised layers.

A research study was designed and conducted to evaluate the applicability of using crystalline silica-rich material as a co-additive with calcium-based stabilisers to treat sulfate-rich expansive soils. Extensive laboratory tests were conducted on lime-treated sulfate-rich soils, with and without crystalline silica admixture, to evaluate the improvements in engineering properties, including swell strain, unconfined compressive strength and resilient moduli properties. The influence of co-additive dosage, curing period and duration of moisture exposure was studied to gain insights into the behaviour of treated soils. Supplementary mineralogical and microstructural studies including X-ray diffraction, scanning electron microscope imaging and differential scanning calorimetry studies were performed on the treated soils to detect the formation of ettringite mineral and cementitious gel compounds. Test results indicated that the use of crystalline silica facilitated enhancement of both the strength before and after capillary soaking, and the resilient moduli properties, while suppressing ettringite mineral formation and associated free swell strains in the treated soils. Mineralogical and engineering studies showed the dominance of pozzolanic activity between lime and crystalline silica over ettringite formation and hence contributed to the effective stabilisation of sulfate-rich soils. Overall, the paper provides a comprehensive understanding of the role of crystalline silica admixture for mitigating deleterious sulfate heaving in lime-treated soils.

Durability is a major concern for all stabilised materials as it can reduce the structural capacity of pavement layers. One of the primary factors influencing the long-term performance of stabilised subgrade layers is moisture. The structural properties of these engineered materials starts to deteriorate with ingress of external water. The detrimental effect of soaking depends on the level of pozzolanic reaction achieved by the stabilised layer prior to water intrusion. Although the affinity for water is reduced after stabilisation, some amount of water is held within the matrix by the precipitated Calcium Silicate Hydrate (C-S-H) phases due to their inherent water adsorption capacity. The extent of damage in turn depends on the type and concentration of different cementitious phases due to the structural, compositional and morphological differences. This study tries to determine the type of hydrated cementitious phase that is more resilient to moisture-induced damage. Results indicate the presence of C-S-H II phase to be beneficial for durability of lime-treated soil when compared to C-S-H I phase.

Civil infrastructure constructed on expansive soils undergoes distress and loss of serviceability because of damage caused by moisture-induced volumetric changes. Traditional stabilization methods that employ calcium-based stabilizers are widely used mitigate the volume change-related distresses, but they increase the carbon footprint and emission of greenhouse gases during production and construction stages, compromising the treatment’s sustainability. This research study was designed to use silica-rich waste products, such as a quarry dust admixture with a calcium-based stabilizer, to enhance the performance of problematic soils and improve the sustainability of the system. An array of engineering tests, including unconfined compressive strength tests before and after moisture conditioning, one-dimensional free swell tests, and linear shrinkage tests, were performed on untreated and treated soils. Test results showed that the utilization of quarry dust as a co-additive significantly improved the strength and durability of the soil and reduced the shrink-swell potential to a greater extent than lime treatment alone. The sustainability assessment was then performed, which showed that the application of quarry dust can be considered a sustainable alternative that helps reduce the geoenvironmental problems related to handling and stockpiling waste products in landfills. Overall, silica-rich waste products have the potential to be appropriate and sustainable additives that work well with a traditional calcium-based stabilizer to modify expansive soil.