Mechanical performance of low-carbon ultra-high performance engineered cementitious composites (UHP-ECC) with high-volume recycled concrete powder

Reusing recycled concrete powder (RCP) from construction waste for ultra-high performance engineered cementitious composites (UHP-ECC) markedly enhances its sustainability. This paper explores the mechanical properties and environmental benefit of low-carbon UHP-ECC containing high-volume RCP as the replacement of cement, ground granulated blast furnace slag (GGBS) and silica sand. The results indicate that UHP-ECC has a loose microstructure when a high percentage of cement is replaced with RCP, while replacing silica sand with RCP results in a denser microstructure. Substituting 75% of cement with RCP reduces the compressive strength and flexural strength of UHP-ECC by 28% and 17.6%, respectively. Substituting RCP for silica sand and GGBS does not significantly affect the compressive strength of UHP-ECC, albeit slightly reducing its flexural strength. Under the application of uniaxial tensile loading, the introduction of RCP improves the ductility of UHP-ECC at a 25% substitution rate, whether replacing silica sand or binder materials. However, as the substitution rate increases, replacing cement and silica sand with RCP decreases the ductility of UHP-ECC. Specifically, reductions of 10% and 7.6% in ultimate tensile strain are discerned when substituting 75% of cement and 100% of silica sand with RCP in UHP-ECC, respectively. Conversely, substituting a large volume of GGBS with RCP can further enhances the ductility of UHP-ECC, with an 15.5% increase in ultimate tensile strain when replacing all GGBS with RCP. By adjusting the RCP content to serve as an alternative to traditional binders and sand, it is possible to achieve a more sustainable UHP-ECC characterized by ideal mechanical strength and ductility, and RCP-blended UHP-ECC demonstrates favorable environmental and economic benefits.