Understanding the roles of Li2CO3 in a sulphoaluminate cement system at negative temperatures

To overcome the slow development of mechanical strengths of sulphoaluminate cement (CSA) in winter construction, this paper investigates the effects of different amounts of admixing Li2CO3 on the setting time, compressive strength, and cooling curve of CSA paste in negative temperatures (−5 °C, −10 °C, and −20 °C). The influence of admixing Li2CO3 on the hydration process and microstructure of CSA paste in a negative temperature environment is also studied using X-ray diffraction (XRD)-Rietveld quantitative analysis, Thermogravimetry (TG) analysis, and Scanning electron microscopy (SEM) observation. The results show that adding Li2CO3 into CSA can significantly improve the mechanical properties at an early age, shorten the curing time, and reduce the freezing point under negative temperatures. The XRD-Rietveld and TG analysis indicates that adding Li2CO3 can increase the consumption of C4A3S̅ and promote the generation of AFt at negative temperatures. It is recommended that the optimum dosage of Li2CO3 should be 0.16 wt% when used as an admixture for CSA systems in negative temperatures.