The recovery of lateritic gravel contributes to the reduction of road construction costs and environmental impact. These materials are of particular interest in road construction because of their abundance, especially in tropical countries, as in the case of Congo. The results obtained on the soils of ʽʽTSANGA and TSIAKIʼʼ show an identical appearance of the two particle size curves, with more fines in the TSANGA sample. Both soils are moderately plastic and their properties predispose them to mechanical treatment (TSIAKI soils) and hydraulic binders (TSANGA soils). The lateritic gravels of TSIAKI can be used as road sub-base for medium traffic while those of TSANGA as sub-base for low traffic. The geotechnical properties of the two samples differ due to the mineralogy, petrography and microstructure which vary from one deposit to another. The SEM microstructure study shows two matrices completely made of kaolinite and the matrix facies are cemented by hematite. X-ray microscopy and SEM allowed the differentiation of goethite and hematite to distinguish the two forms of iron oxides. The TSIAKI soil has a normal iron oxide content (mainly goethite), and has less quartz and kaolinite, which could justify its high CBR index.