The Effect of Initial Water Saturation on Freeze-thaw Damage of Submerged Mortar Materials

An indispensable condition for the occurrence of the freeze-thaw (F-T) damage in unsaturated cement-based materials is that the specimens absorb water during the F-T process and reach a critical level of water saturation, which is influenced by the initial degree of water saturation (IDWS). However, the fast-freeze method commonly used in the laboratory does not reflect the effect of the IDWS on F-T damage. Thus, this study investigated the effect of different IDWS on the development of F-T damage in specimens to fill the gap in this research area. In this study, compressive strength tests were used to characterize the development of damage, while SEM and MIP tests were used to identify the damage at a microscopic level. A reasonable explanation for the damage development was suggested using the critical satiation theory as well as the negative-temperature pumping effect. According to the experimental and discussed results, damage developed more rapidly in specimens with a low IDWS compared to specimens with a high IDWS. The rapid development of damage was not only related to the hydrostatic pressure during the F-T process, but also the osmotic pressure generated during the entry of external water. As the IDWS decreased, the negative-temperature pumping effect of the specimens became more pronounced. Therefore, a lower IDWS led to a higher osmotic pressure caused by the entry of external water and faster development of damage. This, in return, created more water transfer paths and accelerated the process of reaching the critical level of water saturation, significantly weakening the F-T resistance of the specimen.