Development of industrial-grade -C₂S binder from limestone and sandstone: Preparation, properties, and microstructure

This paper developed a cost-effective and highly carbonatable industrial-grade gamma-C2S binder sintered from limestone and sandstone, aiming to advance the industrialization of gamma-C2S binder in construction fields. The carbonation behavior of the industrial-grade gamma-C2S binder, including the evolution of carbonation kinetics, compressive strength, phase composition, and microstructure with carbonation duration was studied. Results showed that a temperature of 1400 degrees C and limestone-to-sandstone mass ratio of 2.1 can be regarded as the optimal sintering regime, which can secure a relatively complete self-pulverization of industrial-grade gamma-C2S binder. The industrial-grade gamma-C2S binder had a milder carbonation reaction, which can reduce the evaporation of water and lead to 48% greater compressive strength, compared to that sintered from analytically pure reagents. During carbonation, the proportion of gamma-C2S phase significantly decreased, while the proportions of CaCO3 and silica gel notably increased in the first 1 h, followed with a slight change in proportions of those phases with the carbonation further extending to 24 h. Similarly, the degree of carbonation rapidly increased to 36.3% in the first 1 h, followed with a slight increase to 43.7% at 24 h. The carbonation of industrial-grade gamma-C2S, accompanied with the precipitation of CaCO3 on gamma-C2S phase surface and the bond of silica gel among CaCO3 grains, contributed to the formation of nacre-bionic interlocking brick-mud microstructure. This led to the rapid enhancement of compressive strength with carbonation of industrial-grade gamma-C2S.