Effect of different environments on the self-healing performance of Ultra High-Performance Concrete – A systematic literature review

Ultra-High-Performance Concrete (UHPC) has been the subject of tremendous research over the years and is being used in a higher and higher number of engineering applications, especially in highly demanding structural service scenarios, thanks to both its superior mechanical performance and likewise significant durability in the un-cracked state. However, as a cement-based material, also UHPC in service condition almost unavoidably works in a cracked state, though its signature tensile behavior allows damage to be spread into multiple thinly opened and tightly spaced cracks instead of localizing it into a single wider crack. Cracking can lead to dete-rioration of performance, particularly when UHPC structures are exposed, as above, to harsh environments. The development of self-healing concrete technologies in recent years, has opened new possibilities to enhance the durability of UHPC in cracked state, empowering with additional capabilities its inborn autogenous self-healing capacity, which is due to the synergy between its peculiar mix-design composition (high binder content and low w/b ratios) and the signature crack pattern as above. It is therefore important to explore the development of self- healing properties of UHPC under different scenarios, not only as a mean to regain the impermeability lost upon cracking but also to retain the (tensile) mechanical performance over time, which also results into the capacity of slowing down the degradation of the overall structural performance. This paper reviews the existing self-healing technologies used in UHPC and summarizes the self-healing properties and their effect on mechanical properties of UHPC when exposed to different environments, also including salt water, geothermal water, wet/dry and freeze/thaw cycles and low temperatures.