Influence of petrology on geotechnical characteristics of lateritic gravels from Lolabe-Campo area (Atlantic Ocean, Cameroon) and their valorization in road construction

The influence of geochemical composition on the geotechnical properties of lateritic gravels was studied to determine their suitability for use in road construction. The research focused on materials from the Atlantic coast of Lolabé-Campo, South Cameroon, which formed on variable rocks (micaschists, metasyenites, quartzites, and gneisses). Petrological analyses, including petrography, X-ray fluorescence (XRF) and scanning electron microscopy (SEM) were carried out and supplemented by geotechnical analyses. Petrography correlated with the materials' geochemistry, while XRF confirmed by SEM results, assessed the degree of alteration. The findings revealed that, depending on the parent rocks, the gravels consist of one, two, or three types of nodules. Lateritic gravels of metasyenites and quartzites, richer in iron with lower silica-aluminum-iron indices (S/R), contain coarser iron particles and exhibit more pronounced red brown and black tones of cortex, cores and fine matrices than the gravels of micaschists and gneisses. The index of lateritization values (IOL), adapted to advanced weathering phases, suggest that gravels developed on metasyenites and quartzites are more weathered. This geochemical variability leads to a wide range of geotechnical properties. The geotechnical analysis revealed that not all these gravels meet the technical specifications for subbase layers. Principal component analysis showed that the Califonian Bearing Ratio (CBR) positively correlated with SiO ₂ and negatively with Fe ₂ O ₃ along with coarse particles. The knowledge of geochemistry allows for better selection and use of lateritic gravels in road construction. Given the scarcity of compliant materials in some areas the world over, these technical specifications should be revised.