Enhancing cracking resistance of ultra-high-performance concrete slabs using steel fibres

Abstract

This study investigates the effect of steel fibres on early-age shrinkage cracking behaviour of ultra-high-performance concrete (UHPC) slabs. For this, four large UHPC slabs, 2600 mm long and 80 mm deep, are fabricated. Two different UHPC mixtures with and without steel fibres (Vf = 0% and 2%) are considered. Test results show that all UHPC slabs without steel fibres exhibit shrinkage cracks at a very early age (before 1 d), whereas no shrinkage cracks are found in the UHPC slabs with steel fibres. The two principal reasons for these observations are the higher shrinkage strain and lower tensile strength of UHPC without steel fibres compared with its counterpart with steel fibres incl. Restrained shrinkage strain is found to be much lower (approximately 75% or more) than the free shrinkage strain, and exhibits a completely different behaviour to that of strain under free conditions.