Coupled heat, air, and moisture transfer in concrete structures is of great practical importance in many fields of civil engineering. Modeling these phenomena, especially in fresh concrete structures or concrete elements exposed to fire, is a complex problem. Several nonlinear phenomena, such as heat and mass sources associated with hydration or dehydration processes, phase changes, hysteresis of sorption isotherms, material properties dependent on moisture content, and temperature and gas pressure, should be taken into account. A new two-dimensional finite element model of coupled heat, moisture, and air transfer in deforming porous building materials HMTRA is briefly presented. Different physical mechanisms governing the liquid and gas transport in the pores of partially saturated porous materials are clearly distinguished. Phase changes, hydration-dehydration processes, and related heat effects are taken into account as well. Temperature and moisture content dependent properties of the fluids and of the solid phase are considered. Also, the effect of material damaging on its intrinsic permeability is taken into account. This finite element model allows for the simulation of the evolution of temperature, gas pressure, moisture content, the global kinetics of the concrete maturing process, as well as stress and strain behavior. Some examples of computer simulations concerning hygrothermal behavior of two-dimensional concrete structures in various conditions are presented. Hygrothermal behavior of a matured concrete element, taking into account the hysteresis of sorption isotherms, is modeled. Temperature and moisture distribution in a fresh concrete structure and their influence on hydration process evolution are analyzed. Performance of a concrete element exposed to fire is simulated.

Authors: Dariusz J. Gawin, D.Sc.; Bernhard A. Schrefler, D.Sc.

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001