Multiscale evaluation of W/B, supplementary cementitious materials, and SAC on the rheological, shrinkage, and microstructural properties of SUHPC

This study systematically investigates the effects of water-to-binder ratio ( W/B ), supplementary cementitious materials (SCMs) composition, and calcium sulfoaluminate cement (SAC) substitution on the rheological behavior, shrinkage performance, mechanical properties, and microstructural evolution of sprayed ultra-high-performance concrete (SUHPC). Three W/B , varying proportions of silica fume (SF) and fly ash microspheres (FAM), and different SAC substitution rates were compared. Rheological results indicated that increasing the SF content or partially replacing ordinary Portland cement (OPC) with SAC significantly enhanced the yield stress and plastic viscosity. A 10 % SAC content increased yield stress by 1.8 times and plastic viscosity by 2.6 times. Concentrated early-stage exothermic reactions under a rapid setting induced significant autogenous shrinkage in SUHPC. Replacing 5 % OPC with SAC reduced autogenous shrinkage by 41.6 %. Under accelerated curing conditions, all mixtures achieved compressive strengths exceeding 60 MPa at 1 d and 120 MPa at 28 d. However, excessive SF increased porosity and microcracking, leading to strength reduction. Microstructural analysis revealed: X-ray diffraction (XRD) and thermogravimetric analysis (TGA) confirmed that SAC (at 5 % and 10 % dosages) promoted AFt formation. Mercury intrusion porosimetry (MIP) ndicated that the AFt generated by SAC filled the pore spaces, increasing the gel pores (