Geological, geotechnical, and mechanical characterization of lateritic gravels from Eastern Cameroon for road construction purposes

Petrographic, mineralogical (X-ray diffraction), and chemical analyses performed on granite-derived lateritic gravels of the Ngankè–Bonis road section show that those materials consist of quartz (26–41 wt%), kaolinite (30–41 wt%), goethite (10–14 wt%), hematite (9–11 wt%), and gibbsite (7–8 wt%). The values of the relative rock virtual weathering degree (30.03–43.12%), potential importance of free aluminum (18.85–19.57%), and potential importance of free ferric iron (18.65–23.08%) indicate that these materials are poorly to moderately altered, plastic, and clearly rupture under loading. The values of the silica/sesquioxide ratio (2.65–3.68 > 2) indicate that these lateritic gravels are suitable for use as sub-base layer materials. The geological data are corroborated by the results of geotechnical and mechanical tests on those materials: fine particles 18–30%, liquid limit 53–64%, plasticity index 22–32%, California bearing ratio 47–69%, uniaxial compressive strength 1.22–1.28 MPa, and tensile strength 0.80–0.84 MPa. A combination of 25–30 wt% of grain-fraction 5/20 granite aggregates (Los Angeles abrasion <30%) with 70–75 wt% of lateritic gravels provides concrete with California bearing ratio values of between 82 and 87, thus making the studied materials of Ngankè–Bonis area suitable for use as base layers on roads ranging from Cameroon to the Central African Republic.