Abstract
Concrete is widely used for construction materials in various area over the world. However, degradation has been caused under the severe conditions that drying and freezing - thawing action. A shrinkage reducing agent （SRA）has been to prevent the dry shrinkage. However, some researchers reported that the concrete added SRA is degraded extremely by the freezing and thawing actions. The cause of degradation have been scantly studied. Previous research can predict the expansion / contraction behavior of the saturated cement paste during freezing process considering three different driving forces：hydraulic pressure, crystallization pressure and negative water pressure. However, it did not predict expansion / contraction behavior during thawing process and also that of unsaturated cement paste during freezing and thawing process. This paper aims to predict freezing-thawing induced strain for both saturated and unsaturated cement pastes. The new integrated model was proposed, which is the combination of the previous model with the new model that contained the vapor phase. That is derived from thermodynamic equilibrium condition and fracture mechanics. Previous model is used for prediction of freezing-induced strain at saturated condition, while new model is used for thawing-induced strain at saturated condition, and freezing-thawing induced strain at unsaturated condition. Our theoretical predictions were compared with experimental expansion and contraction results during thawing process at saturated condition, and good agreements were obtained. It can be also seen that the strain behavior during freezing and thawing cycles can predict accurately by our prediction model.
