Effects of calcium nitrite and polycarboxylate ether on belite-ternesite-calcium sulfoaluminate cement properties

The extremely short setting time and relatively poor rheology performance of belite-calcium sulfosilicate-sulfoaluminate cement (BTCSA) slurry hinder its large-scale cast-in-situ application. This study investigated the coupling effects of polycarboxylate superplasticiser (PCE) and calcium nitrite additions on the fluidity, setting times and compressive strengths of BTCSA. The hydration kinetics and microstructural evolution of BTCSA were characterised using isothermal conduction calorimetry, X-ray diffraction and scanning electron microscopy analysis. The results showed that the setting times were extended. The additions of PCE and calcium nitrite were more effective in enhancing the fluidity than using PCE alone. The optimal dosages were 0.4% PCE and 0.8% calcium nitrite. The initial setting time was 90 min, the final setting time was 113 min and the fluidity achieved 238 mm. The compressive strength reached 74.6 MPa in 3 days and 121.1 MPa in 60 days. The early-age hydration was delayed but the degree of hydration within 3 days of curing was enhanced. A denser microstructure with linear and columnar calcium sulfonate crystals was formed, and the early-age compressive strength was enhanced.