Time-dependent characterization of Na2CO3 activated slag

This study aims to investigate the time-dependent characteristics of sodium carbonate activated slag at the early stage and its compressive strength development. The reaction kinetics of Na2CO3 activated slag is analyzed at the curing ages of 1h, 6h, 1d, 2d, 3d, 4d and 7d, respectively, and the reaction products are characterized employing FTIR, XRD, TG-DTG and SEM. The results show that a weak reflection of gaylussite is observed after 1 d of curing, while intensive accumulation of gaylussite and formation of hydrotalcite are observed at 2 d/3 d. Meanwhile, the gelation of C-(A)SH after 3 d of curing is identified by FTIR. The role of pH, CO32− anion concentration and the formation of crystals such as gaylussite and hydrotalcite on the reaction process are discussed. In addition, a relationship between the initial alkali concentration and compressive strength at different curing ages of 7 d, 28 d and 180 d is derived.