Study on the Influence of Supplementary Cementitious Materials on Fast Hardening Sulfoaluminate Cement–Engineered Cementitious Composites

To enhance the application effect of engineered cementitious composites in rapid repair engineering, this study prepared early strength and fast hardening sulfoaluminate cement–engineered cementitious composites (S-ECC) with sulfoaluminate cement as the matrix, fly ash, silica fume, and desulfurization gypsum as supplementary cementitious materials (SCMs), and added polyvinyl alcohol (PVA) fiber. The effects of fly ash, silica fume, and desulfurization gypsum on the performance, fiber dispersion, mechanical properties of drying shrinkage, and microscopic mechanism of S-ECC were systematically studied. The results indicate that the fiber dispersion in silica fume–S-ECC (SF-S-ECC) improves as the fly ash content increases. When the fly ash content reaches 30%, the ultimate tensile strength of SF-S-ECC at each age is the highest. The SF-S-ECC with 40% fly ash exhibited the lowest drying shrinkage of 9.3×10−5 at 28 days. The addition of silica fume enhanced the fluidity of fly ash–S-ECC (FA-S-ECC), and the ultimate tensile strength of the FA-S-ECC sample containing 5% silica fume reached 6.17 MPa after 60 days of curing. The addition of 5% and 10% desulfurization gypsum in FA-SF-S-ECC resulted in excellent tensile properties. The most important thing is to avoid reduction of the strength of the repair material in later stages. Fly ash, silica fume, and desulfurization gypsum can make up for the slow development of S-ECC strength, allowing the S-ECC of the three systems (SF-S-ECC, FA-S-ECC, FA-SF-S-ECC) to hydrate rapidly in the early stage, produce a lot of AFt and hydration product, and enhance the strength of materials. Cracks, pores, and other defects in the hardened slurry can hinder later-stage strength development.