Investigation on the mechanical characteristics of multiscale mono/hybrid steel fibre-reinforced dry UHPC

Abstract

Dry ultra-high performance concrete (DUHPC) is a promising building material with better mechanical and durability properties, developed on the basis of retaining the advantages of traditional dry concrete, such as fast hardening speed, high early age strength and rapid demoulding. In the current study, the impacts of multiscale mono and hybrid steel fibre reinforcements on the static mechanical behaviour of DUHPC were further studied based on the benchmark mix ratio and optimal curing regime obtained from the previous study. The experiments carried out included the quasi-static uniaxial compression, four-point bending and split-tensile tests. The mono fibre reinforcement (0.5–2.0 vol. %) comprised of straight steel fibres with the same diameter but different lengths (6, 10 and 13 mm), while the hybrid fibre reinforcement was composed of different combinations of foregoing fibres at a fixed content (1.5 vol. %), which could be further divided into double and ternary hybridization. Test results revealed that compared to control samples without fibre reinforcement, the single addition of any steel fibres improved the static mechanical behaviour of DUHPC, particularly for flexural and split-tensile performance. In the case of fibre hybridization, the replacement of longer fibres with more addition of short (6 mm) ones evidently reduced the flexural toughness and energy absorption capacity of DUHPC upon cracking, whereas the mixtures with hybrid medium (10 mm) and long (13 mm) fibres as well as with hybrid short, medium and long fibres showed better compressive toughness and energy absorption capability. The proposed multivariate regression linear, nonlinear and most of the mixed models could well estimate the compressive, flexural and split-tensile strength values of mono steel fibre-reinforced DUHPC at a given range of fibre length, volume content and curing age. The updated best-fit models containing compressive strength as an additional independent variable performed better in predicting both the flexural and split-tensile properties.