High-Temperature Effect on the Physical and Dynamic Compressive Properties of Pre-Stressed Cement Mortar

Cement mortars are extensively used in tunnels and underground facilities, where the risk of high temperatures due to fires and explosions triggered by traffic accidents, earthquakes or electrical malfunctions cannot be ruled out. It is necessary, therefore, to know the mechanical properties of cement mortars at high temperature in both static and dynamic conditions. The dynamic mechanical behavior of pre-stressed cement mortars at high temperature is investigated in this research project, from 25 to 300 degrees C, by means of the Hopkinson bar. The microstructure of cement mortars is also studied via Scanning Electron Microscopy-SEM. The properties under investigation are: density, coefficient of thermal expansion, dynamic compressive strength, peak strain, dynamic elastic modulus and damage variables, as well as the longitudinal wave velocity. The tests indicate that the physical and dynamic mechanical properties of cement mortars are significantly affected by high temperature. In the range 25 - 300 degrees C, because of the increasing number and size of the microdefects (microcracks), the density and the longitudinal wave velocity exhibit a gradual less-than-linear decline, while the decline of the compressive strength and elastic modulus is more marked (roughly linear), the peak strain and damage almost increase linearly.