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 (<10 nm) while reducing the medium capillaries (10–50 nm), thereby mitigating shrinkage. These findings provide theoretical and practical guidance for SUHPC, particularly for underground engineering and repair applications that require high early strength and dimensional stability. • Investigated effects of W/B, SF–FAM ratio, and SAC substitution on SUHPC rheology, shrinkage, and strength. • Demonstrated that SF enrichment increases yield stress and autogenous shrinkage. • Revealed SAC reduces autogenous shrinkage by up to 52.1 % through AFt formation and pore refinement. • Showed that optimal 5–10 % SAC substitution maintains high strength while lowering carbon footprint. • Established microstructure–performance links via TGA, XRD, SEM, IC and MIP analyses for SUHPC design.
Wu et al. (Fri,) studied this question.