Thermodynamics of Crystallization Stresses in DEF

The thermo-mechanics of damage during delayed ettringite formation have been examined. A thermodynamic approach is used to evaluate the supersaturation under which ettringite may form and the crystallization pressures that may result. From these stresses at the pore scale and with the amount of ettringite forming, an average hydrostatic tensile stress in the solid is calculated and compared to the tensile strength of tested samples. Results indicate that, when the loading rate dependence of tensile strength is taken into account, it is possible to rationalize factors that do or do not contribute to damage, such as ettringite content, temperature and fly-ash content. Although a number of important assumptions are made and clearly indicated in the paper, the results do open a new perspective onto durability studies which goes beyond the sole case of delayed ettringite formation.