Development of internal moisture transfer and cumulative residual strain in concrete under freeze-thaw cycles

Abstract

Freeze-thaw (F-T) damage is one of the common types of damage in concrete durability problems. The use of sensors to monitor the health of concrete during freeze-thaw conditions can offer real-time information about the status of concrete. In this study, fiber Bragg grating (FBG) sensors were used to record the strain and temperature histories of concrete specimens under F-T cycles. The results of the experiments demonstrated that during the F-T process, the concrete specimen exhibited different extremes on the temperature at the center and the top position. By calculating the cumulative residual strain, it is found that the cumulative residual strain at top position of the top-exposed specimen stops growing after 50 freeze-thaw cycles, while that of the top-sealed specimen keeps growing slowly within 200 freeze-thaw cycles. After 100 freeze-thaw cycles, the cumulative residual strain at the center position of both coating regimes began to increase, although the rate of increase was larger for the top exposed specimens than for the top sealed specimens. High water saturation of pores caused by internal water migration is the main factor leading to residual strain in concrete during freeze-thaw. The X-ray computed tomography (CT) analysis revealed that both the number of pores and the average pore size progressively decreased from the surface to the center.