Self-healing capability of ultra-high-performance fiber-reinforced concrete after exposure to cryogenic temperature

This study aims to examine flexural performance and self-healing capability of ultra-high-performance fiber-reinforced concrete (UHPFRC) after exposure to cryogenic temperature. To evaluate the effects of fiber type and curing condition on the flexural and self-healing properties, straight steel fibers with three different aspect ratios of 65, 97.5, and 100 and twisted steel fiber with an aspect ratio of 100 were incorporated into ultra-high-performance concrete (UHPC) mixture at identical volume fraction of 2% and two different curing processes (i.e., 3-day air curing and 28-day water curing) were applied. Test results indicate that incorporating the straight steel fibers with higher aspect ratios was more effective in enhancing the flexural performance of UHPC as compared to the short straight and twisted steel fibers. The UHPCs with straight steel fibers also exhibited better self-healing capacities than that with twisted steel fibers after exposure to cryogenic temperature. Just the 3-day air curing was enough for the UHPCs including straight steel fibers with aspect ratios of 65 and 97.5 to completely recover their flexural performance to the original level, while the 28-day water curing was even insufficient for that with twisted steel fibers to be fully recovered after cryogenic cooling. From a scanning electron microscopy with energy dispersive X-ray spectroscopy analysis, the cracks were filled with calcium carbonate (CaCO3), and the smaller cracks were more efficiently filled with the CaCO3, compared to the larger cracks.