Sinterization and hydration of synthesized cement clinker doped with sulfates

This paper aims to evaluate the influence of three kinds of sulfates from the green production of cement on its sintering and hydration. The properties of clinker and hydration were monitored by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction, X-ray fluorescence and isothermal conduction calorimeter. Results indicate that gypsum lowers the decomposition temperature of CaCO₃ and all these Sulfates will enhance the solid-phase reaction but increase melting temperature. Sulfates reduce the content of C₃S, but K₂SO₄ and 2CaSO₄·K₂SO₄ is conducive to the formation of β-C₂S. The hydration induction period is shortened by the sulfates. K₂SO₄ and 2CaSO₄·K₂SO₄ improve the early hydration of clinker, but gypsum may lightly reduce the hydration reactivity of clinker in acceleration period. 2CaSO₄·K₂SO and K₂SO can significantly accelerate the compressive strength development of cement clinker before 3 d; by contrast, gypsum is detrimental for that. The precipitation of hydration products (CH and C–S–H) in clinker with sulfates is more than that of clinker without sulfates at 9 h. K₂SO₄ can accelerate the hydration of clinker without forming ettringite.