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Australian design practice for granular pavements with lime-modified subgrades is very conservative and does not consider the initial and long-term strength improvement. It recommends that the assigned California bearing ratio (CBR) of a modified subgrade soil should not exceed 15% for most roads. Two types of clay soils with plasticity indices of 22% and 42.5% were treated herein with their minimum lime demand (MLD) and tested to evaluate the modification influence on their properties. These properties include pH, compaction, compressive strength, bearing capacity, resilient modulus, and permanent deformation. Three different mellowing periods, 24, 48, and 72 h, between lime treatment and compaction, were used in this study to identify their optimum mellowing periods. Analysis of testing results for long-term compressive strength and CBR showed that MLD improves both soils' compressive strength and bearing capacity. Using the actual CBR values of lime-treated soils in designing the cover over subgrade results in a 30% reduction in pavement thickness. Lime modification of these soils also improves their resilient moduli and permanent deformation. The best results are achieved with mellowing periods of 24 h for Soil A and 72 h for Soil B. These optimum mellowing periods reduced permanent deformation of Soil A to less than 0.15% and 0.11% for Soil A. Considering the study findings, it is believed that thinner pavements can be designed and built on modified subgrades with MLD, which will help road agencies save funds. [ABSTRACT FROM AUTHOR]

Nowadays, for soil stabilisation and cleaner production of geo-composites, the possibility of utilizing waste rubber is in vogue. The present paper deals with experimentally investigating the mechanical and micro-structural characteristics of weak Indian clayey soil partially substituted with lime (0–3.5%) and waste rubber tyre powder (0–15%). It was observed that, with increasing lime and rubber powder content, the plasticity index of the soil decreases. The shear strength and compaction testing results reveal that adding lime and rubber tyre powder (RTP) enhances the geotechnical performance of clayey soil up to an optimum dosage value. Also, the tri-axial shear testing was performed to obtain stress-strain curves for all considered soil mixes. For modified clayey soil containing 3% lime and 12.5% rubber powder, the cohesion values and bearing capacities improved phenomenally by 36.1% and 88.6% respectively, when compared to clayey soil. Further for this mix, SEM analysis reveals a compacted microstructure which improves dry-density and California's bearing ratio among all modified mixes. The novel co-relations upon regression analysis are found able to predict plasticity index, dry density, bearing capacity and shear strength with higher confidence levels. Overall, the cost-benefit analysis worked out to obtain the optimum cost of construction of footings and flexible pavement shows cost deductions up to 19% and 39% respectively while utilizing modified clay soil mixes containing 3% lime and 12.5% rubber powder in subgrade, ultimately making production stronger, cheaper and environment friendly. • Experimental investigations on finding synergistic performance of clayey soil, lime and waste rubber tyre powder. • Atterberg's limits, shear, compaction, CBR, & microstructural characteristics shows better performance of modified mixes. • Optimised clay-lime-RTP mix reports 44% and 88.63% improvements in shear strength and bearing capacities respectively. • Decrement in productional cost of up to 39% for modified geo-mixes in road pavement and foundation constructions. [ABSTRACT FROM AUTHOR]