Rheology, mechanical properties and pore structure of sprayed ultra-high performance concrete (SUHPC) with viscosity-enhancing agent

Abstract

• Rheological properties of SUHPC with 50 mm sprayed thickness were investigated. • Comparison between mechanical properties of SUHPC and poured UHPC. • 3D pore structures of SUHPC and UHPC were clearly observed by CT test. • Deflection-hardening curves of SUHPC and UHPC were measured and analyzed. A sprayed ultra-high performance concrete (SUHPC) with suitable sprayed thickness due to the addition of a viscosity-enhancing agent based on the designed UHPC has been developed in this research. The internal relations among the high viscosity, spraying process, mechanical properties and pore structure of SUHPC were revealed and discussed. Appropriate air bubbles and high viscosity slurry greatly improved the pumping and spraying of fresh SUHPC, the sprayed thickness could be up to 50 mm when the relative thixotropy of SUHPC matrix was 5 times based on poured UHPC. For the harden SUHPC, the strength and toughness of it were both slightly decreased than that of UHPC containing the same fiber content (1.5 %), including compressive strength was 109.2 MPa, decreased 20 % compared with UHPC, and exhibited the deflection-hardening behavior (excellent toughness) under four-point bending loading. Additionally, the porosity of SUHPC was increased than UHPC containing the same fiber content (1.5 %), both mainly distributed among 3–20 nm in micro-pores, but air bubbles would be easily trapped into fresh SUHPC due to the spraying process and high viscosity, transformed into macro pores in hardened SUHPC matrix.