This study focuses on the physico-mechanical and geotechnical properties of natural gravels and granite collected from two localities in the Kouilou Department (Congo). The research was conducted on two deposits of natural gravels, located respectively in Malélé and Boubissi, as well as on a crushed granite deposit in Louvoulou. The main objective was to optimize the physico-mechanical and geotechnical characteristics of these materials, or to highlight their specific performance criteria, with a view to their rational use in public works—particularly for their integration into road pavement structures.A comprehensive testing program was carried out, including identification tests, mechanical tests, and road performance tests (Los Angeles and Micro-Deval), in order to determine the geotechnical and mechanical properties of the materials. The results show that all three materials have low natural moisture contents. The materials were classified into well-defined particle size ranges: 0/40 mm for the Malélé gravels and the Louvoulou granite, and 0/31.5 mm for the Boubissi natural gravel. Proctor compaction tests revealed excellent compactability for all the studied materials, with high maximum dry densities (greater than 2.0 g/cm³) and moderate optimum moisture contents.The California Bearing Ratio (CBR) tests indicated moderate bearing capacities, allowing the materials to be classified as medium-bearing soils (class S4 according to road classification standards). Regarding road performance tests, the natural gravels from Malélé and Boubissi yielded generally satisfactory results, though stabilization (through hydraulic binders or additives) is required to fully meet the standards prescribed by the Los Angeles abrasion and Micro-Deval fragmentation tests. The crushed granite from Louvoulou, on the other hand, exhibited excellent performance in all road-related tests, confirming its robustness, wear resistance, and dimensional stability.Overall, the results demonstrate that the studied materials possess physical, mineralogical, and mechanical characteristics compatible with their use in the lower layers of pavement structures. Their application is recommended for use in subgrade, sub-base, and possibly base layers, particularly under low to moderate traffic conditions.
