A comprehensive review on effects of mineral admixtures and fibers on engineering properties of ultra-high-performance concrete

The unparalleled attributes of ultra-high-performance concrete (UHPC) reported over the last three decades sum up the development of this material in two phases: UHPC and ultra-high-performance fiber-reinforced concrete (UHP-FRC)/ultra-high-performance hybrid fiber-reinforced concrete (UHP-HFRC). The integration of scientific knowledge pertaining to material interactions and technical observations of developed UHPC has laid the foundation for further research and development. Microstructural research has revealed the contribution of finer sizes mineral admixtures along with lower water/binder ratios in the range of 0.16–0.24 to the development of high-density calcium silicate hydrate with a very low possibility of ettringite formation and alkali silica reactions in UHPC matrix. The addition of fibers is challenging when seeking to maintain the rheology of UHPC; therefore, technically sound concrete experts are required for the field applications. The challenges preventing the widespread use of UHPC are the higher initial cost, the requirement of special skilled labor for execution, and the lack of open discussions about various UHPC standards available worldwide to reach an agreement on minimum strength achievements and test standards. The hurdles hindering the use of UHPC in recent emerging 3D printing technology are also discussed in the present study. The vast literature compilation also reveals that less research has concentrated on UHP-HFRC as compared to UHPC and UHP-FRC. Therefore, a comprehensive review regarding the effects of mineral admixtures and fibers on the microstructural characteristics, fresh properties, and mechanical properties overall to address the upcoming challenges preventing the widespread use of UHPC and UHP-FRC/UHP-HFRC is essential.