Mechanistic and comparative laboratory assessment of lime dosage and uniaxial geogrid on the strength and durability of classified lateritic subgrade

This study presents a mechanistic and comparative laboratory assessment of lime stabilization and uniaxial geogrid reinforcement, applied independently and in combination, to improve the engineering performance of a classified A-7-6 (CL–ML) lateritic subgrade from Ogun State, Nigeria. The objective was to evaluate the effect of lime dosage and geogrid inclusion on the short- and long-term California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), and Resilient Modulus (MR), and to test the hypothesis that chemical and mechanical stabilization mechanisms act synergistically to enhance stiffness and durability. Quicklime (CaO > 90%) was added at 2–8% by dry weight, while the geogrid used was uniaxial polypropylene with an aperture size of 30 mm and tensile strength of 22 kN/m. Specimens were prepared by mixing, compacting, and curing at 25 ± 2 °C and 95 ± 2% RH for 7, 14, and 28 days, then tested according to ASTM and AASHTO standards. Each condition was replicated thrice, and the data were analyzed using one-way ANOVA (p < 0.05). Results showed that lime treatment reduced the plasticity index from 30 ± 1.2 to 6 ± 0.5%, increased UCS from 300 ± 15 to 950 ± 40 kPa and improved soaked CBR from 23 ± 1.1 to 57.5 ± 2.3% after 28 days. Single and double geogrid layers enhanced soaked CBR to 33 ± 1.4% and 43 ± 1.7%, respectively, with negligible strength loss after three moisture cycles, confirming durability under wetting–drying conditions. Combined lime–geogrid stabilization achieved the highest performance, with CBR > 65%, MR > 90 MPa, and UCS > 1.0 MPa, exceeding AASHTO subgrade requirements. The findings demonstrate that lime primarily enhances chemical bonding, whereas geogrid reinforcement improves mechanical confinement; their combination offers a durable, cost-effective, and low-carbon alternative to conventional cement stabilization for tropical lateritic subgrades.