Development of eco-friendly ultra-high performance concrete by synergistic utilization of quaternary blends: Towards enhanced dynamic performance and lower environmental impact

Incorporating supplementary cementitious materials (SCMs) into ultra-high performance concrete (UHPC) is an effective approach to promote properties and reduce CO2 emissions. Nevertheless, excessive utilization of SCMs can negatively impact mechanical performance. A deeper understanding synergistic effects of SCMs from micromechanics to dynamic behaviors could contribute to developing eco-friendly UHPC with enhanced impact resistance and lower environmental impact. Here, the hydration products, pore structures, micromechanics of interfacial transition zone (ITZ), dynamic properties and environmental impact of UHPC with binary, ternary and quaternary blends are evaluated. Results indicate that the synergistic effect of quaternary blends could optimize the bonding properties of ITZ between steel fibers and matrix as well as densify the microstructure by generation of higher percentage of ultra-high and high density C-S-H, thus enhancing the dynamic strength and impact resistance. The better micromechanics properties of ITZ delay the occurrence of initial cracks, resulting in the slightest damage degree under similar strain rate. More homogeneity of the microstructure of the matrix and better micromechanical properties of ITZ results in a lower dynamic increase factor (DIF). A predictive model of DIF for UHPC is established considering strain rates and the synergistic effect of SCMs. Finally, the environmental analysis reveals that the quaternary blends can significantly improve environmental friendliness by reducing carbon footprint.