Mineralogical Characterization of Unbound Granular Material (UGM) Used as Road Base Layers in Côte d’Ivoire

Abstract

This study characterizes Unbound Granular Material (UGM) used in road construction in Côte d’Ivoire through macroscopic and microscopic petrographic observations of composite samples from fifteen quarries. Results reveal a predominance of granite consistent with the local Birimian bedrock. Based on mineralogical composition and texture, the UGM are classified into four groups: biotite-dominant granites, alkaline granites, a granodioritic facies, and simple granites. The primary mineralogy is dominated by the quartz–feldspar–biotite assemblage, where biotite represents the weakest phase. Observed alteration processes—muscovitization, sericitization, chloritization, and epidotization—affect grain surface properties and increase moisture sensitivity. Biotite-rich granites with extensive muscovitization (>40%) are expected to show reduced bearing capacity and higher abrasion susceptibility. Alkaline granites and granodiorites affected by sericitization are likely to exhibit decreased performance under wet conditions. These findings highlight the decisive role of mineralogical composition and alteration intensity in predicting UGM durability in tropical road construction.