Effect of fibre on properties of UHPC containing metakaolin and limestone or quartz powder

This study comprehensively investigates the effect of steel fibre (STF) level on air content, flowability, mechanical strengths, drying shrinkage, chloride ion permeability, and pore structure of ultra-high performance concrete (UHPC) containing metakaolin and limestone powder (LP) or quartz powder (QP). The results indicate that air content and fluidity of fresh UHPC continuously decrease with STF level growth. Its compressive and flexural strength generally increase with STF level. STF addition can impose a greater improving effect on the compressive strength of QP-contained UHPC compared with LP-UHPC. Conversely, the flexural strength and ductility of LP-mixed UHPC under various levels of STF are bigger than those of the corresponding UHPC specimen containing QP. A moderate STF dose would relieve the drying shrinkage tendency of UHPC under 50% relative humidity and water-curing regimes. Moreover, the shrinkage value and chloride ion permeability for LP mixtures containing various levels of STF under water curing are smaller than those of QP-incorporated UHPC. The late-age flexural strength of LP-contained UHPC linearly increases with reduction of air content, and a good linear regression equation is obtained for conveniently predicting the flexural strength according to air content.