A review on ultra high performance concrete: Part II. Hydration, microstructure and properties

•The hydration process of binders in UHPC is similar to that in ordinary concrete.•UHPC has a very low porosity.•The mechanical properties of UHPC are much better than that of ordinary concrete.•UHPC has a character of superior durability.

Ultra high performance (UHPC) is a new cement based material, and it has aroused interest around the world since it was introduced in the early 1990s. Part I reviewed the theoretical principles, raw materials selection, mixture design and preparation techniques for UHPC. This part II reviewed the hydration, microstructure, mechanical properties, dimensional stability and durability of UHPC. Finally, some needs for future studies of UHPC are suggested. The portlandite of UHPC is much lower than that in the normal concrete. Heat curing could promote secondary hydration between mineral admixtures and Ca(OH)2, and xonolite was formed when the temperature was over 250 °C. UHPC has a very low porosity, especially under heat curing. UHPC has a character of high strength, stiffness and superior durability, etc.