Internal Curing by Porous Calcined Bauxite Aggregate in Ultrahigh-Performance Concrete

Abstract

Ultra-high performance concrete (UHPC) has more severe autogenous shrinkage than ordinary concrete, which may lead to increased cracking risks. Thus, a suitable and effective agent for internal curing (IC) of UHPC without a negative effect on the strength is needed to solve this problem. A type of strong and porous aggregate made of calcined bauxite was used in this study to achieve low shrinkage and lower-cement UHPC based on the modified Andreasen and Andersen model, and together, a reference mixture made of basalt aggregate was prepared. The autogenous shrinkage of UHPC with basalt aggregate reached 570 μm/m at the age of 28 days, while the autogenous shrinkage of the UHPC with calcined bauxite was substantially reduced or a slight expansion occurred. This was found to be due to the internal curing effect provided by the calcined bauxite aggregate. A pronounced 56-day compressive strength of 148 MPa was achieved for this standard-cured UHPC without steel fibers. The low shrinkage UHPC internally cured by calcined bauxite aggregate can be applied to on-site cast UHPC structures or bridge decks that are prone to shrinkage cracking.