Abstract: This paper investigates the effect of steel fiber's zinc phosphate (ZnPh) treatment and shape on the strength and toughness of ultra high performance concrete (UHPC) containing granite powders under autoclaved curing. Steel fibers with four dfferent shapes were used: straight with copper plating (S), single-linear hooked-end with copper plating (G1), bi-linear hooked-end with copper plating (G2) and crimped with copper plating (L). The results obtained from customized single steel fiber pullout test and SEM-EDS observation indicated that the mechanical interlock is the dominating effect for the enhanced strength and toughness of UHPC containing granite powders. The average bonding strength and pullout energy are in the order of G1>G2>L>S. The ZnPh treatment modified the fiber geometry, resulting in enhanced surface roughness, which increased the chemical bonding and static friction between the steel fibers and the UHPC matrix, and consequently raised the pullout energy of steel fibers in UHPC. Compared to G1, G2 and L steel fiber, the ZnPh treatment exhibited the most obvious effect toward S steel fiber in terms of enhanced toughness of UHPC.
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2017, Vol. 31 
