Observation on microstructure and shear behavior of mortar due to thermal shock

Abstract

The shear behavior of intact and pre-flawed mortar is investigated after heating to high temperature (maximum of 900 °C) and cooling down to room temperature slowly in the oven or rapidly in water. The color change, mass loss, XRD analysis, and the thermal cracking of mortar after high-temperature treatment are discussed in detail. Experimental results show that, as exposed temperature increases, thermal-induced cracks propagate and open up, and structural damage is more serious under water-cooled conditions due to the intense and sudden thermal shock. Flawed specimens are more vulnerable to thermal shock than the intact specimens. Internal fracture models obtained from CT techniques show that, for intact specimens, thermal-induced cracks mainly occur near to the edges of specimens and propagate to the inner side. While for specimens containing internal flaws, thermal-induced cracks initiate first at the tips of pre-existing flaws and propagate to the edges. The shear strength of mortar after high-temperature treatment are accorded with the Mohr-Coulomb (M − C) criterion. The peak shear strength and shear modulus show a distinct degeneration over exposed temperature, and is influenced by cooling treatment. Specifically, rapid cooling treatment can aggravate the deterioration of shear mechanical properties in mortar.