Synthesis of low-carbon alkali-activated materials using carbonated recycled concrete fines with sodium meta-aluminate

Abstract

This paper reports the synthesis of a novel low-carbon alkali-activated material system to fully utilise the reaction potential of carbonated recycled concrete fines. The hydration mechanism and strength source of the alkali-activated carbonated recycled concrete fines (AACRCF) system are systematically investigated. The results indicate that the AACRCF paste can pose competent hardening properties comparable to OPC, with 28-day compressive strengths reaching up to 25 MPa and 90 MPa at W/S ratios of 0.5 and 0.2, respectively. The hydration of the AACRCF system typically exhibits characteristics of high kinetics and low reaction heat release, mainly including the carbo-aluminate reaction and alkali-activation reaction, which convert the calcium carbonate and silica-alumina gels in CRCF into monocarboaluminate and C-N-A-S-H gels. The strength of this system mainly comes from its crystalline phase rather than the gel phase. Overall, the utilisation of the AACRCF system can considerably reduce carbon emission, resulting in significant environmental benefits.