Effect of 3D, 4D, and 5D hooked-end type and loading rate on the pull-out performance of shape memory alloy fibres embedded in cementitious composites

Abstract

This paper investigates the single fibre pull-out performance of superelastic shape memory alloy fibres (SMAFs) embedded in a highly flowable cementitious matrix suitable for producing ultra-high performance fibre reinforced cementitious composites. The research emphasis is placed on the influence of hooked-ends and loading rate on the pull-out behaviour of SMAFs. Full-range pull-out load-slip responses are captured for straight and 3D, 4D, and 5D hooked-end SMAFs under three loading rates ranging from 0.025 mm/s (representing quasi-static loading) to 25 mm/s (representing seismic loading). Pull-out test is also carried out on steel fibres (SFs) of similar geometries as SMAFs for comparison reasons. Pull-out responses are analysed in terms of maximum tensile stress in the fibre, material usage factor, pull-out energy, average and equivalent bond strength. The results obtained show lower pull-out resistance for SMAFs comparing to their steel counterparts. Although the use of more bends at hooked-end of SFs (5D versus 3D) significantly enhances the average and equivalent bond strength of SFs at a given loading rate, its efficiency was much lower for SMAFs. The deformation process that fibres undergo when they travel through the matrix tunnel can explain such a difference between SMAFs and SFs. Experimental results show loading rate dependency for pull-out resistance of hooked-end SMAFs in terms of both average and equivalent bond strength. In contrast, loading rate dependency is observed only for equivalent bond strength in the case of straight SMAFs.