Petrographic and Geotechnical Study of Aggregates from the Alfallé Magmatic and Metamorphic Massif (Central Chad )

Abstract

This study focused on aggregates from the geological formations of the Alfallé massif located approximately 75km east of the town of N'Goura, in the Hadjer-Lamis Province (13°N, 17°E). The aim of this study is to determine the petrographic and geotechnical characteristics of these aggregates with a view to their recovery. Petrographically, the massif outcrops in blocks, balls and slabs. It is made up of three types of rock: alkali feldspar megacrystalline granite, biotite mi-crogranite and biotite gneiss. Alkali feldspar megacrystalline granite is composed of quartz (30%), orthoclase (30%), plagioclase (20%), biotite (15%) and opaque minerals (≈5%). Biotite mi-crogranite is composed of quartz (15-20%), orthoclase (20-25%), plagioclase (18-25%), biotite (20-25%) and opaque minerals (≈4%). The biotite gneiss is composed of quartz (25-30%), alkali feldspars (25-27%), plagioclase (17%), biotite (25-27%) and opaque minerals (≈5%). The geotech-nical characteristics show that the aggregates studied have specific density values of between 2.58 and 2.75g/cm3 with an average value of 2.66g/cm3, bulk density of 1, 3 to 1.4g/cm3 with an av-erage value of 1.3g/cm3, a Los-Angeles coefficient of 11.2% to 28.9% with an average value of 20.1% and a wet Micro-Deval coefficient of 5.2% to 10.8% with an average value of 7.6%. The values obtained indicate that the materials studied have satisfactory properties, with the excep-tion of samples E4 and E1, which respectively show aggregates with excellent geotechnical prop-erties and materials with limited impact resistance. These results are conclusive and of scientific interest for the exploitation of an aggregates quarry.