Evolution mechanism of spatial damage of mortar in the early freeze-thaw stage

Abstract:

Affected by the direction of temperature and moisture transfer, the damage development of mortar in the early freeze-thaw (F-T) stage exhibits spatial characteristics. However, existing F-T damage monitoring methods mostly focus on the overall average performance of specimens, ignoring the differences in local damage evolution. To quantitatively evaluate the influence of spatial position on the early F-T damage of mortar and further reveal its evolution mechanism, this paper proposed a real-time and in-situ strain monitoring method based on fiber bragg grating sensors and tested the strain at different spatial positions inside mortar during the early F-T stage. Results show that the strain amplitude in the upper layer of mortar is higher than that in the middle layer during the early F-T stage; with the increase of F-T cycles, the peak strain continues to rise, and residual strain appears; micro-morphology analysis results verify the reliability of using residual strain to judge the spatial difference of F-T damage. Based on this, this paper further established an early F-T damage evolution model considering spatial position. The comparative analysis results of macroscopic performance tests and local strain show that the damage of mortar in the early F-T stage is dominated by surface cracking. Although this phenomenon has little effect on the degradation of macroscopic performance, it can provide new transmission channels for environmental moisture to enter the interior of mortar, further aggravating the evolution of F-T damage.