Influence of external water introduced by coral sand on autogenous shrinkage and microstructure development of Ultra-High Strength Concrete (UHSC)

Abstract

Ultra-High Strength Concrete (UHSC) is a new cement-based material with high strength and durability, which has broad application prospects in practical engineering. The biggest disadvantage of UHSC is relatively large early autogenous shrinkage and high cracking risk. Coral sand as an internal curing agent employed in UHSC can effectively inhibit the self-desiccation inside the concrete and reduce its autogenous shrinkage. In this paper, 0–0.6 mm river sand is replaced by the same size of pre-wetting coral sand, and the early autogenous shrinkage and microstructure development of UHSC are evaluated. The experimental results show that the introduction of wet coral sand improves the fluidity of UHSC fresh slurry and prolongs the setting time. Meanwhile, the development of mechanical properties and early autogenous shrinkage of UHSC hardened paste are inhibited as a whole. Image analysis of pore structure presents that the porosity of micron-scale pores in UHSC increases, and that porosity of millimeter-scale pores decreases. Environmental Scanning Electron Microscope (ESEM) and Electron Backscattered Diffraction (EBSD) photomicrographs show that with an optimized amount of induced water, the Interfacial Transition Zone (ITZ) of damp coral sand and matrix could be homogenized and densified, which cause the propagation of micro-cracks in UHSC is difficult.