In Burkina Faso, the most commonly used road construction material is lateritic soil. However, in its raw state, this soil does not meet the required recommendations. To overcome this problem, previous studies have often focused on improving these soils by adding cement. However, these studies have rarely included a multi-criteria characterisation of the main geomechanical parameters of treated soils. It was also noted that the identification parameters of lateritic soils could have an influence on their improvement with cement. The aim of this study is to highlight the influence of the physical and mineralogical properties of lateritic soils on the effectiveness of improving their geomechanical properties by adding a low content of cement (<3% wt.). The soils were taken from two sites: Saaba (LAS) and Kamboinsé (LAK). The effects of cement addition on the plasticity index, CBR index, Young's modulus, unconfined compressive strength, tensile strength and shear strength were studied. In their raw state, LAS and LAK have different physical properties and cannot be used as sub-bases. The addition of cement improves the overall physical and mechanical properties of both soils, but to different degrees. Indeed, after adding 3% cement to the raw soils, the CBR index of LAS increases by 1275% compared with 257% for LAK; the unconfined compressive strength of LAS is twice as high as that of LAK, and the Young's modulus increases by around 460% for LAS compared with 360% for LAK. After improvement, these two soils met all the CEBTP specifications except for tensile strength. The effect of cement was more significant on LAS due to its better physical properties and higher clay mineral content, which would improve pozzolanic reactivity during cement hydration. Knowing the mineralogy of lateritic soils when treating them with cement would allow us to reduce the quantity of cement, thereby mitigating its negative impact on the environment.
Keywords: base layer; cement addition; geomechanical properties; lateritic soils; physical properties; road construction.