Pore Pressure and Drying of Concrete at High Temperature

A mathematical model for water transfer in concrete above 100°C is developed. Drying tests of heated concrete are reported and material parameters of the model are identified from these tests as well as other test data available in the literature. It is found that water transfer is governed principally by the gradient of pore pressure, which represents the pressure in vapor if concrete is not saturated. Permeability is found to increase about 200 times as temperature passes 100°C, which could be explained by a loss of necks on migration passages. The pore volume available to free water increases as dehydration due to heating progresses and as the pore pressure is increased. The temperature effect on pressure-water content (sorption) relations is determined. Thermodynamic properties of water are used to calculate pore pressures. A finite element program for coupled water and heat transfer is developed and validated by fitting test data.