STUDY ON WATER ABSORPTION MODEL OF AIR-ENTRAINING CONCRETE UNDER NATURAL CONDITIONS

The freeze-thaw damage of air-entraining concrete in natural environment is caused by the intrusion of external water and the saturation process in the capillary pores and air-entraining voids. By discussing the process of air dissolution and diffusion, a revised absorption model is built based on Fagerlund's classic long-time absorption theory. The air-entraining mortar absorption test is performed to validate the improved model. Considering the drying–wetting actions, the absorption model of air-entraining concrete in natural environment is proposed. This model consists of two phases: the water intake in natural environment affected by drying and wetting; the saturation of pore-voids system by external water intake. The water intake under natural drying-wetting cycles is evaluated through the concepts of moisture influential depths and equilibrium drying–wetting time ratio. The pore-void saturation process employs the revised absorption model to predict the change of the saturation degree. Afterwards, the two-stage freeze-thaw service life model is applied to a major railway construction project. On the basis of the local meteorological data and of the predetermined characteristics of structural concrete, the key design parameters are obtained with respect to the frost actions and the expected service lives.