Thermal Effect on Micro Properties of Granite Aggregate in Concrete

Identification and selection of the type of rock used as coarse aggregate in concrete exposed to high temperature is important from a standpoint of strength and safety of existing concrete structures. The present work documents the microscale behavior of granite coarse aggregates and its influence on strength parameters of concrete, exposed to different temperatures ranging from 425 to 850[degrees]C (797 to 1562[degrees]F) for an exposure time of 2 to 4 hours. Factors leading to decomposition of coarse aggregates in concrete under thermal loads were obtained using petrographical scannign electron microscopy (SEM) and electron probe micro analysis (EPMA) techniques. At temperatures ranging from 425 to 550[degrees]C (797 to 1022[degrees]F), the damage in concrete is gradual and is attributable to mortar shrinkage and separation of mortar-aggregate interface. Thermodynamic modeling results have shown that, beyond the formation temperature (715[degrees]C [1319[degrees]FJ), minerals in the rock start to melt and migrate along the fracture planes, causing sudden reduction in load-carrying capacity in concrete. Keywords: coarse aggregate; concrete (high-temperature exposure); melt identification; petrography and microanalysis; strength reduction; thermodynamic modeling.