Insight of key parameters in freeze-thaw damage on the performance of cement-based materials: A comparative study with rapid-freeze method

The degree of saturation (DOS) and water transport have significant influences on the F-T damage in cement -based materials. However, as a traditional test method, the regime of the rapid-freeze method restricts sealing conditions and the DOS before the F-T process (named initial degree of saturation: IDOS) of the specimen. In this study, the effects of IDOS and sealing conditions on the F-T damage were investigated by modifying these two conditions of the rapid-freeze method. The dynamic elastic modulus and compressive strength test results demonstrated that the unsealed specimens were more sensitive to IDOS in the water environment compared to the sealed specimens. For the unsealed specimens, a negative correlation relationship between the IDOS and the loss of the mechanical indicators for the unsealed specimens was originally disclosed in this work, which is opposite to the regularity for the sealed specimens reported in previous studies. Furthermore, the unsealed specimens with low IDOS exhibit greater F-T damage, implying that in the water environment, reducing the IDOS required by the rapid-freeze method will create harsher F-T conditions. In addition, decreasing the IDOS of the specimen results in a changed pattern of development of the compressive strength loss rate of the specimen. As supplement examinations, microstructure analysis (including TG, SEM, and MIP tests) was performed. Furthermore, a new mechanism of IDOS and sealing conditions on F-T damage was presented.