Geomechanical and Thermal Properties of Lateritic Gravels for the Design of Road Pavements in Tropical African Environments

Current road design techniques in tropical Africa, based on estimated geomechanical moduli, do not ensure adequate road durability. The objective of this study is to investigate the geomechanical and thermal properties of lateritic gravels for the design of flexible pavements in a tropical African environment. Repeated load California Bearing Ratio, unconfined compression test, X-ray diffraction, and thermal tests were used to characterize lateritic gravels. These soils have a plasticity index ranging from 19.15 to 25.82%, a maximum dry density between 1.7 and 1.9 g/cm3, and a California Bearing Ratio between 21 and 31%. A comparison between the calculated empirical moduli (130–155 MPa) and immersed resilient (62–98 MPa), immediate resilient (122–144 MPa), stiffness (31–50 MPa), and Young’s moduli (61–115 MPa) revealed that the calculated empirical moduli have the highest values. These comparisons showed that Young’s modulus and stiffness would overestimate pavement thickness and increase construction costs, which would not be beneficial for the environment. These soils were found to contain gibbsite, goethite, kaolinite, hematite, anatase, ilmenite, quartz, maghemite, rutile, and boehmite. A loss of thickness of the subbase layer in the range of millimeters was estimated at 50°C, based on the mass loss recorded through thermodifferential and thermogravimetric analyses. Empirical moduli, commonly used in Africa, and immediate resilient moduli could result in low pavement thickness and lead to early failure of the pavement structure. Therefore, the use of empirical, immediate resilient, stiffness, and Young’s moduli is not recommended for road durability. Instead, the immersed resilient modulus is recommended in the road design process as it can contribute to pavement durability.