Effects of anti-foaming admixture on properties of ultra-high performance concrete

This paper aims to investigate effects of anti-foaming admixture (AFA) on air content, flowability, mechanical strength and microstructure of ultra-high performance concrete (UHPC). UHPC mixtures were prepared with two water-binder ratios of 0.17, 0.2 and three AFAs (XP1, XP2, XP3) were added by 0.05-0.4% of the mass of binder. Results reveal that the air content of fresh UHPC mixture decreases whit the incorporation of AFA and XP1 behaves the best decreasing effect. The compressive strength of UHPC added with AFA is increased and XP2 presents the best effect. The decrease of water-binder ratio from 0.2 to 0.17 doesn’t lead to an increase in compressive strength due to the more air bubbles entrapped in very low water-binder ratio mixture. A good exponential relationship (f=a*x^b) can be found between compressive strength and entrapped air content. The incorporation of AFA decreases the coarse pore content (>100nm) and air bubbles with diameter bigger than 100μm in hardened specimen, playing a positive role in optimizing pore structure and improving strength.