Resilient crystalline admixture in ultra-high performance self-healing concrete under cyclic freeze-thaw with de-icing salts

Ultra-high performance (fibre-reinforced) concrete (UHPC) is recognised for its mechanical properties, such as tensile strain hardening, and exceptional durability, including autogenous healing capabilities due to, among others, the addition of supplementary cementitious materials and fibres. However, it is unknown how the cracked concrete can deal with freeze-thaw (FT) cycles with de-icing salts and if healing agents added to the mix could improve the durability of this type of concrete. This study investigates the influence of a crystalline admixture (CA) in UHPC under FT conditions with focus on single cracks with a width of around 120 μm, specifically focusing on the ability of the healing products of CA to survive and the ability to re-heal after a healing regime following FT exposure. The results revealed that UHPC incorporating healing agents exhibited remarkable resilience against cyclic FT conditions. These healing agents successfully generated healing products that provided exceptional resistance to FT-induced damage and demonstrated the capability to undergo rehealing after exposure to FT.