Investigating the textural and physico-mechanical response of granites to heat treatment

This study investigates the petrographic changes associated with heat treatment of texturally variant granites from northwest Pakistan. The corresponding effects on the physico-mechanical properties have also been analyzed. Detailed microscopic observations distinguish collected rocks into (i) Alkali feldspar micro-porphyritic variety of Ambela granite (AFG) (ii) coarse grained Malakand granite (MG) (iii) mega-porphyritic Utla granite (UG). The non-destructive tests including ultrasonic pulse velocity, Schmidt rebound hardness, porosity, specific gravity and water absorption of studied granites are markedly influenced by temperature variation. Particularly at temperature >= 600 degrees C, a drastic decreasing trend observed with temperature rise. Significant instability in minerals has been noted with increasing temperature shown by the initiation of thermally induced fractures and widening of pre-existing cracks. Pre-existing fractures in major minerals including feldspars and quartz expand with increasing temperature accompanied by the novel fractures induced due to high thermal stresses that also effects the physical and mechanical properties. The relatively more altered UG is more prone to textural changes associated with heat treatment and the effects can be seen at lower temperatures than other studied fresh granites.