Effects of sodium sulfate on the hydration and properties of lime-based low carbon cementitious materials

Abstract

To reduce the carbon footprint and energy consumption from the cement manufacturing industry, lime-based low carbon cementitious materials (LCM) has caught strong attention. LCM as a novel low-carbon cement shows impressive performance and promising prospects; however, its mechanical properties are inferior to those of ordinary Portland cement (OPC). In this study, different dosages of sulfate sodium was incorporated into LCM to investigate the effects of sodium sulfate on LCM performance. The properties and hydration of LCM with and without sulfate sodium were systemically investigated and analyzed. The results revealed that LCM blending with 2–3 wt% sodium sulfate showed the best mechanical performance. The compressive strength of LCM containing 3 wt% sodium sulfate was increased by 57.0% and 20.8% relative to the plain LCM at 3 d and 90 d, respectively. Microstructural characterization showed that a great amount of ettringite had formed at 3 d, which effectively improved the mechanical performance of LCM at early stage. Moreover, the addition of sodium sulfate effectively accelerated the hydration of the solid waste in LCM, and more hydrated lime was consumed in the hydration process. The ettringite became embedded in C(A)SH gel with increasing curing age, which resulted in a dense microstructure of hydrated paste with fewer coarse pores and an enhancement in the mechanical performance of LCM. Thus, the sodium sulfate effectively increased the strength of LCM at both early and later stage.