Functionalized carbon nanotube enhanced carbonation efficiency of carbide slag to develop a sustainable carbonate source for low-clinker limestone calcined clay cement (LC3)

To address the early-age strength degradation of low-clinker limestone calcined clay cement (LC3), this study developed a highly reactive and sustainable carbonate source by enhancing the CO 2 mineralization efficiency of carbide slag (CS) through utilizing carboxyl-functionalized carbon nanotubes (CNT-COOH) as growth template. Results showed that the CNT-COOH significantly accelerated the carbonation kinetics of CS. With a 2% dosage of CNT-COOH (by mass of CS), the Ca 2 + concentration in the CS slurry decreased to 410.17 mg/L at 10 min, which was 41.15% lower than that of the reference group. This is because the CNT-COOH induced heterogeneous nucleation of calcite crystals, resulting in a more porous CaCO 3 product layer on the CS surface, thereby providing more channels for the diffusion of CO 2 and Ca 2+ . In low-clinker LC3 systems, the modified CS significantly accelerated hydration kinetics, leading to a 23% and 13.4% increase in the compressive and flexural strength at 1d, respectively. Furthermore, the proportion of harmful pores at 28d was decreased by 20.7%. This is attributed to the promotion of carboaluminate precipitation by the modified CS, as well as the pore refinement resulting from the filling effect of CNT-COOH. This study aims to provide a stable carbonate source for low-clinker LC3, thereby promoting the low-carbon transition of the construction industry.