Effect of ultra-fine fly ash on the mechanical and shrinkage properties of ultra-high performance concrete

This paper reports on a study to determine the possibility of using ultra-fine fly ash (UFA) for partial or total replacement of normal fly ash (NFA) in ultra-high performance concrete (UHPC). Workability, microstructure, porosity, drying shrinkage as well as mechanical properties were comprehensively studied to investigate the influence of UFA on UHPC. The fly ash, which was a compound of NFA and UFA with various mass fractions, had a total content of 30 wt%. The results demonstrated that compressive strength is enhanced if NFA is partially or totally replaced with UFA. Compared to the reference mixture containing 100 wt% NFA, incorporating UFA into UHPC has been shown to improve its workability. Contrarily, adverse effects on drying shrinkage were discovered when NFA is substituted with UFA.