Effect of ultra-fine supplementary cementitious materials on the properties of calcium sulfoaluminate cement-based ultra-high performance concrete

Ultra-high performance concrete prepared by calcium sulfoaluminate cement (CSAC-UHPC) possesses promising applications because of its excellent early strength, durability and environmental benefits. However, the impacts of supplementary cementitious materials (SCMs), an important components for UHPC, on the properties of CSAC-UHPC remain ambiguous in international research. To well complement this subject, effects of three ultra-fine SCMs, ground granulated blast furnace slag (GGBFS), limestone powder (LP) and silica fume (SF), on the properties of CSAC-UHPC were investigated, including flowability, setting time, hydration process, microstructure and mechanical strength. Results showed that the flowability of CSAC-UHPC increased with the GGBFS and LP content increasing, respectively, and decreased with the SF content increasing. Meanwhile, the addition of GGBFS, LP and SF had a limited regulation of the setting time, with the initial and final setting time between separately 13—26 min and 19—35 min, but it inhibited the hydration of CSAC-UHPC and reduced the total amount of hydration products, among which the effect was most pronounced by SF. Moreover, the replacement to cement with 10 % mass fraction of GGBFS, LP and SF, individually, could refine the pore structure of CSAC-UHPC, and further increasing the replacement rate was detrimental to the development of micromorphology. The content of GGBFS and LP should not exceed 10 % without compromising the mechanical strength of CSAC-UHPC, while SF was not suitable for addition. The flexural strength at 4 h of CSAC-UHPC with 10 % GGBFS and LP reached 8.1 MPa and 7.9 MPa, and the compressive strength at 4 h reached 49.4 MPa and 48.1 MPa, respectively. Also, they have a carbon footprint reduction of approximately 25—40 % and an embodied energy reduction of approximately 25—35 %, compared to ordinary UHPC.