Effects of multi-scale hybrid fibre reinforcement on the mechanical properties of ultra-high-performance concrete

An experimental investigation was conducted on the effects of multi-scale hybrid fibre reinforcement incorporating steel fibre and wollastonite fibre on the mechanical properties (compressive strength, tensile splitting strength, flexural toughness, and direct tensile properties) of ultra-high-performance concrete (UHPC). The results indicate that, compared with macrofiber reinforcement, the use of hybrid steel fibres (HSFs) (macrofibers and mesofibers) significantly improved the strength and toughness of the UHPC. In addition, the higher the dosage of mesofiber, the better the effect of the HSFs. Longer mesofibers were found to provide better performance in terms of interfacial bonding strength between the fibres and the UHPC matrix, leading to an increase in the anti-cracking effect of the HSFs, and hence improvement in the tensile splitting strength and flexural toughness of the UHPC. Moreover, adding wollastonite fibre as microfiber in addition to HSFs enhanced the mechanical properties of the UHPC. This may be related to the respective anti-cracking effect of three types of fibre and their synergistic snubbing effect, as well as the filling effect of wollastonite fibre and the chemical bonding effect caused by the reaction between wollastonite fibre and calcium hydroxide in the paste.