FEASIBILITY STUDY OF THE ANDESITE’S AND GRANITES EXPOSED IN THE GHIZAR DISTRICT, GILGIT-BALTISTAN BY USING PETROGRAPHIC AND PHYSIO-MECHANICAL APPROACHES

Abstract

Present study focuses on the petrographic and physio-mechanical viability of the volcanic and plutonic igneous rocks (andesite and granites) exposed in the north-western district of Gilgit-Baltistan, for its usage as coarse aggregate in construction work. Geologically, the investigated area lies along the collisional zone between Eurasian Plate and Kohistan Island Arc, that is why rocks along this boundary are highly deformed and metamorphosed. Exposed rock types include basalts, andesite, granites, meta-igneous and meta-sedimentary. Bulk rock samples were collected from different quarries of andesites and granites for detail physio-mechanical investigations. Petrographic observation reveals that the investigated rock samples are comprised of quartz, biotite, hornblende, epidote, muscovite and plagioclase. Most of the quartz grains exhibited undulose extinction, representing deformation of the quartz grains as a result of active tectonic activities. Physio-mechanical properties of these rock samples were acquired as per national and international standards i.e., American Society for Testing Material (ASTM), American Association of state Highway (AASHTO) and National Highway Authority (NHA) Specifications. It has been noticed that the analytical data observed from sieve analysis, specific gravity, absorption, porosity, flakiness and elongation, Los Angeles abrasion, and soundness lies in the acceptable and specified limits. Petrographic investigation demarcates that the exceeded percentage of deformed/reactive silica (i.e., >10%) in most of the inspected samples claims that these samples are not feasible for coarse and fine aggregates in concrete work. Reactive silica accelerates reaction between silica and concrete, causes weak bonding between concrete and aggregate, ultimately result in failure of major structures.