Pore pressure in heated concrete walls: theoretical prediction

Abstract

Synopsis Pore-water pressures in concrete can be calculated by a previously developed theory which is based on thermodynamic properties of water and takes into account the huge changes in permeability and sorption isotherm with temperature, as well as the changes of pore space due to temperature and pressure. After reviewing the theory, finite-element solutions are com-pared with weight-loss tests of Chapman and England, and theoretical predictions are made for rapid heating of thick walls, either sealed or unsealed. A two-dimensional axisymmetric finite-element solution is developed to analyse theffect of a hot spot on the wall. The pore-pressure peaks are found to be much higher than for slow heating (25 atm versus 8 atm), and still about 50% higher when the heating is confined to a hot spot. The moisture movement in regions where the pressure gradient is opposite to the temperature gradient is found to be rather irregular and to exhibit oscillations. The theory predicts the phenomenon of ‘moisture clog’ suggested by Harmathy on the basis of tests.