Elastic modulus damage model of cement mortar under salt freezing circumstance based on X-ray CT scanning

In this paper, the properties of cement mortar with 0.5 W/C before and after freeze-thaw cycles in 4 wt% NaCl solution were measured. The experiments include mass loss, X-CT scanning and axial compression full curve. Results showed that cement mortar damage under freeze-thaw cycle was a layer-by-layer peeling process from exterior to interior. As the freeze-thaw cycles proceeded, the initial mass loss rate of mortar slowly increased and then the rate rapidly increased, and a mass loss prediction equation was proposed. Using X-ray CT scanning and 3D reconstruction technology, a method for the evaluation of the internal damage rule of cement mortar under freeze-thaw cycles was proposed. The porosity change of sample before and after freeze-thaw cycles was calculated by X-ray CT scanning technology. As the number of freeze-thaw cycles increased, the porosity increment of the samples increased approximately linearly. The peak compressive stress, initial elasticity modulus and residual strength of cement mortar caused by freeze-thaw cycles reduced gradually, and with the increase in cycling number, the downward trend became more obvious. Based on mass loss and the change of internal overall porosity of mortar, an elastic modulus damage model of cement mortar was established which is in good agreement with the experimental results. (C) 2018 Elsevier Ltd. All rights reserved.