Durability of ultra-high performance concrete – A review

Ultra-high performance concrete (UHPC) is more durable than conventional concrete (CC) and high-performance concrete (HPC) owing to the use of low water-to-binder ratio (W/B) of approximately 0.2 and high amount of fine particles. It is an innovative composite material that can serve as a potential candidate for concrete structures exposing to aggressive environments. A comprehensive investigation of the durability characteristics of UHPC is essential to provide fundamental information for material testing requirements and procedures and expand its practical applications. This paper reviews the durability of UHPC in terms of water and chloride-ion permeability, corrosion of steel reinforcement, carbonation, freeze–thaw resistance, chemical attack resistance, alkali-silica reaction, abrasion resistance, and fire resistance. Influential factors, including W/B, curing regime, steel fiber volume, fiber hybridization, specimen size, and testing age, were considered. It is obvious that: (1) UHPC has very low permeability to water and chemical substance, which is about one to two orders of magnitude lower than that of CC and HPC; (2) Carbonation rarely happens on UHPC, either under standard curing or heat curing, after 1 to 3 years exposure. (3) Corrosion of steel reinforcement and alkali-silica reaction are not concerns for UHPC under any curing regime due to its low permeability. (4) UHPC is found to gain increases in mass, strength, and relative dynamic modulus over hundreds of freeze–thaw cycles. (5) Compared to CC and HPC, UHPC is more prone to explosive spalling due to the increase in vapor pressure and non-uniform thermal gradient. Partly or completely filled micro-cracks by carbonation and/or continued hydration of cement are beneficial to improving the mechanical strength and microstructure of UHPC. Hybridization of steel and polypropylene fibers is an efficient approach to mitigate the explosive spalling of UHPC.