Petrographic and geomechanical characterization of the Ngaoundal rock massifs in Adamawa Cameroon for use in road engineering

Construction companies and the local population use the rocks as construction materials without considering their characteristics. However, characterizing these massifs levels before their use is essential to guarantee the quality and durability of the roads built. The purpose of this study is to ascertain the physico-mechanical properties of the rock massifs in the Ngaoundal area in order to ascertain their potential applications in different road construction fields. The methodology used consisted of macroscopic, microscopic and physico-mechanical characterisation of the various rock massifs in Ngaoundal. The rocks studied here are dolerite with a doleritic texture consisting of plagioclase, pyroxene and opaque minerals; granite with a light gray to pinkish appearance; and granite with a grainy to pegmatitic structure, composed of alkali feldspar, quartz, plagioclase, biotite, opaque minerals and finally cataclasites with a dark gray to greenish appearance under the microscope. This latter rock is mostly made up of crystals of quartz, plagioclase, potassium feldspar and amphibole. In geotechnical terms, bulk density varies from 1.416 to 1.502 kN/m3; specific weight varies from 2.625 to 3.33 g/ cm3; dynamic fragmentation varies from 20.30 to 33.10%; impact resistance varies from 24.45 to 44.20% and wear resistance varies from 7.25 to 38.6%. Regarding the materials’ geotechnical characteristics, it seems that, after comparison with geotechnical standards, the dolerite and the granite massif have excellent geotechnical parameters, which allow their use in road construction as materials for bitumen gravel, base courses and wearing courses for low-to-medium traffic T1–T3. On the other hand, the cataclasites encountered in Ngaoundal cannot be used for road construction because this massif is very altered.