Developing sustainable engineered cementitious composites with carbonated recycled concrete fines: Feasibility and engineering properties

Abstract

Using carbonated recycled concrete fines (CRCF) as supplementary cementitious material is an effective way to develop sustainable engineered cementitious composites (ECC). This study systematically explored the effects of CRCF with a substitution rate up to 30 % through mechanical property tests, micromechanical analysis and microstructural characterisation, aiming to elucidate the mechanism of CRCF on ECC. Results suggest that the incorporation of CRCF reduces the mechanical properties of ECC, but a moderate amount (15 %) of CRCF-ECC still performs more than 85 % and 90 % of the tensile and compressive strengths of the reference ECC. Also, the tensile strain capacity of 15CR is increased by approximately 20 %, significantly enhancing the tensile toughness of ECC. The Jʹ b and Jtip of 15CR are approximately 10 % and 6 % higher than those of 15R, respectively. This indicates that the 15CR mixture exhibits superior Griffith crack propagation capability after the initiation of the first crack, which is also recognised as flat crack propagation capability. The incorporation of CRCF significantly improves the average pore size of ECC, mainly attributed to more calcium carbonate on the surface of CRCF, resulting in strengthening of bonding interactions with C-S-H during hydration. This results in stronger fibrematrix bonding and denser microstructure in the microscopic reaction, and in turn enhances the internal structural compactness and strengthens the mechanical properties. The effects and micro-mechanisms of CRCF on the mechanical properties of ECC were comprehensively evaluated and revealed