LAUSR

Abstract Fly ash cenosphere (FAC) is used as a supplementary cementitious material (SCM) to prepare ultra high-performance concrete (UHPC). The replacement of cement with FAC in UHPC is beneficial for the workability of fresh UHPC and from the perspective of mechanical and microstructure development. The influence of FAC with different dosages (0–40% of binders by volume) on the mechanism of strength development was investigated by mechanical, rheological and microstructural measurements. The results indicate that FAC shows a marginal enhancement of the hydration process of UHPC in the early hydration period and the predominant filler effect at 28 days. The additionally formed hydration products from the pozzolanic reaction of FAC contribute to gradually refining the pore structure and slowly increasing the compressive strength of UHPC. While the early-age compressive strength of the UHPC matrix with FAC is inadequate, the ‘ball-bearings’ and water-reducing effect of FAC particles obviously reduce the viscosity in the UHPC paste. FAC can work as an inorganic viscosity breaking agent to improve the flowability of UHPC for a variety of engineering applications.