Mixture design, Preparation and Properties of Lightweight Ultra-high Performance Concrete (LUHPC)

Abstract

In this study, the natural river sand was completely replaced by high strength lightweight sand (LWS) to reduce the density of ultra-high-performance concrete (UHPC). The mixture design and preparation method of lightweight ultra-high performance concrete (LUHPC) was studied based on the principles of particle compaction skeleton stacking and fiber toughening. The P. II 52.5 cement, silica fume and fly ash cenosphere were used as the cementitious materials, and the fine steel fiber was used to improve the mechanical strength and flexural toughness of LUHPC. The effects of the proportion of cementitious materials, water-to-binder ratio (W/S), binder-to-sand ratio (B/S) and steel fiber content on the mechanical key properties of LUHPC were discussed. Results showed that the LUHPC had ultra-high performance and low density (lower than 2090 kg/m3). The microhardness and microstructure analyses of the interface zone between cement matrix and sand indicate a dense transition zone is produced in the presence of pre-saturated lightweight sand, which resulted in the highest compressive strength (114.5 MPa at 28d), flexural strength (16.8 MPa at 28d), and high bending toughness index I20 (21.2).