Characterization of a rehydration phenomenon on cement-based materials containing heat-induced cracks: coupled transport properties and X-ray micro-tomography

Abstract

This study deals with the phenomenon of rehydration in heat-induced macro/micro cracks for a normalized mortar and concrete paste, both having a W/C ratio of 50%. Reyhydration was tested using steady state gas (argon) and ethanol permeability measurements provided by our laboratory, combined with thermo-gravimetric (ATG) and micro-tomographic (CT) analyses. Prior to these experiments, all of the samples were subjected to successive heating-cooling cycles, from a 105°C reference state, up to 600°C. At the macroscopic level, the material's transport properties are determined by means of gas permeability tests, following which the same sample is measured using the ethanol permeability test (after saturation in distilled water and drying at 105°C). At the microscopic level, the pore network of the heat-treated cement pastes is characterized using CT (voxel≈4μm), before and after rehydration in order to assess its 3D profile. This includes quantitative analysis of the crack size, the connected and non-connected pore volume, the pore surface area, as well as the pores' distribution. The self-healing capacity of saturated heat-treated cement-based materials is clearly revealed, when these results are combined with ATG analyses of the material's mineralogical composition. The results show that following heat-treatment, the gas permeability of mortars is of the order of 10 -15 m 2 at 600°C, whereas following rehydration, their ethanol permeability lies in the range between 10 -18 and 10 -17 m 2 , which is quite close to the intact gas permeability of mortar at 105°C. DOI 10.21012/FC9.131 Yan PEI, Frederic SKOCZYLAS and Gregory HAUSS 2 This behavior corresponds primarily to that of self-healing products penetrating heat-treated cracks. During the preceding gas permeability cycle, an increase in confining pressure also contributes to the irreversible closure of cracks. Finally, the results of the ATG, CT, and permeability (gas, ethanol) tests, all of which reveal a rehydration phenomenon occurring in heat-induced cracks, are found to be well correlated.