Effects of Alumina Nanofibers and Cellulose Nanocrystals on Durability and Self-Healing Capacity of Ultrahigh-Performance Fiber-Reinforced Concretes

Ultrahigh-performance fiber-reinforced concrete (UHPFRC) features outstanding durability properties in uncracked state, although its composition based on very low water/cement ratios may result in a higher risk of early-age cracking due to increased shrinkage. This paper, based on research performed in the framework of the H2020 project ReSHEALience, studied aggressive chemical exposure conditions. A UHPFRC reference mix with 0.8% crystalline admixtures (CAs) and two other mixes, one containing 0.25% alumina nanofibers (ANFs) and one containing 0.15% cellulose nanocrystals (CNCs), both by weight of cement, were investigated. This study analyzed the synergy between CA and the nanoconstituents (ANF and CNC) on the physical, chemical, mechanical, and durability properties the and self-healing capacity of uncracked and cracked UHPFRC. The results showed that the presence of nanoadditives improves the mechanical properties independently of environmental curing conditions, refines the pore structure, favors cement hydration, and improves the intrinsic durability with a Cl and water transport reduction. Moreover, in the cracked state, nanoconstituents improved the self-sealing and self-healing capacity of specimens immersed in geothermal water.