Preparation of ultra-high strength concrete for CFST arches

Abstract

The application of ultra-high strength concrete (UHSC) in concrete-filled steel tube (CFST) arches significantly enhances the structural load-bearing capacities. However, to meet the pumping construction requirement and ensure a composite effect between the steel tube and core concrete without debonding, core UHSC should simultaneously achieve ultra-high compressive strength, high flowability, and low shrinkage or micro expansion characteristics. In this paper, the preparation technology for such UHSC is systematically studied. The effects of coarse aggregate, steel fiber, expansion agent, and shrinkage-reducing agent on the compressive strength, flowability, and autogenous shrinkage of UHSC are investigated. The results indicate that UHSC with an appropriate amount of coarse aggregates (0~41.6% replacement ratio by mass) or steel fibers (0~2% by volume) satisfied the target compressive strength and flowability, while the risk of debonding still existed due to the shrinkage of the core UHSC. Optimal performance to prevent debonding is achieved through the combined use of coarse aggregates (21.6%) with hybrid admixtures (10% expansion agent + 1~2% shrinkage reducing agent). A mixed design approach for the core UHSC filled into the CFST arch is finally proposed.