The effects of high temperature heating on the gas permeability and porosity of a cementitious material

This experimental study investigates variations in the transfer properties (permeability) and porosity, of a normalized mortar heated up-to 600 °C. New experimental techniques allow simultaneous measurements of permeability and porosity variations, under confining pressure. The main results show that when temperature raises from 105 °C to 600 °C, the permeability increases by 2 to 3 orders of magnitude, and nearly 50% in relative porosity (from 17% to 24% in absolute value). The higher the temperature, the greater the sensitivity to confinement of the permeability (and porosity), thus indicating substantial cracking and the irreversible nature of the material's behaviour. The application of confining pressure leads to irreversible crack closure and crushing of the pores. Various poro-mechanical measurements also revealed a considerable loss in stiffness for strongly heated material, providing complementary information concerning the porosity variation under loading, the amplitude of which is too high to be due to crack closure alone.