Evaluation of freeze-thaw damage of partially saturated concrete with shrinkage-induced initial damage: Using in-situ CT technique

The western plateau of China is marked by low relative humidity (RH) and experiences over 80 freeze-thaw cycles (FTCs) annually. This low RH contributes to shrinkage-induced initial damage in concrete structures before they enter service. However, the effect of such early deterioration on freeze-thaw damage behavior of partially saturated concrete remains unexplored. To address above challenges, concrete with/out shrinkage-induced initial damage was prepared through standard curing (95 ± 5% RH) and dry curing (40 ± 5% RH) followed by adjusting saturation levels. The tests of macroscopic mechanical properties indicate that the degradation of both residual compressive strength and relative dynamic elastic modulus in sealed specimens after 400 FTCs is less than that of unsealed ones after 100 FTCs. Furthermore, the micro/meso-scale defects of the specimens over increasing FTCs were explored based on in-situ X-ray computed tomography (CT), and average relative spalling amount was newly proposed to assess the freeze-thaw damage. The results showed that the average relative spalling amount of the unsealed concrete with initial damage was 4.4% higher than that of specimens lacked such damage after 100 FTCs. Notably, sealed specimens with a saturation ≥86.6% also exhibited a similar trend. The newly developed damage prediction model incorporating the number of FTCs, curing humidity, and saturation level well predicted the freeze-thaw damage of specimen after FTCs, demonstrating a relative error less than 6.7%. This study aims to pave a theoretical basis for the freeze-resistant design of concrete construction in cold regions with low RH. • shrinkage-induced initial damage aggravates the freeze-thaw damage of concrete. • The freeze-thaw damage of unsealed sample is more serious than those of sealed one. • Propose evaluating method for freeze-thaw damage based on relative spalling amount. • The damage prediction model considers initial damage and saturation effects.