Abstract:In order to study the effect of heating rate on mortar permeability and microstructure, the mortar is heated to 500°C at three heating rates (5°C/min, 10°C/min, 15°C/min).The new experimental technique allows the simultaneous measurement of mortar permeability and porosity with gas under perimeter pressure and the observation of T2 spectral distribution, pore size distribution and fracture evolution of the damaged specimens using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques.The results showed that the mortar gas permeability and porosity gradually increased with the increase of heating rate at 500°C.During loading and unloading of surrounding pressure, the gas permeability of the mortar is more sensitive to the surrounding pressure compared to the porosity.The T2 spectra of the mortars after the action of different warming rates all showed two wave peaks, and the distribution of the main wave peak occupied three orders of magnitude.As the heating rate increases, the pore size distribution of the mortar shifts to the right and the pore size increases.After the action of high temperature, the dense structure of mortar becomes porous and loose, and the faster heating rate, the larger the width of its internal cracks.