Effect of SO3 and MgO on Portland cement clinker: Formation of clinker phases and alite polymorphism

Abstract The effects of SO 3 and MgO on the formation of cement clinker and the polymorphism of alite were thoroughly investigated. Quantitative analysis of the mineral composition was performed using the Rietveld method based on powder X-ray diffraction patterns. Clinkerization of the raw meal was observed by ex-situ experiments. The C 3 S and C 2 S contents were linearly related to the SO 3 /MgO ratio. Adding SO 3 hindered the formation of C 3 S, the formation temperature of which increased by approximately 100 °C. MgO enhanced the formation of C 3 S by both accelerating the clinkerization reactions and lowering the formation temperature of C 3 S. The C 4 AF content increased when MgO was added. Microscopically, MgO led to the formation of small C 3 S crystals, whereas SO 3 enlarged the size of C 3 S crystals and promoted the formation of C 2 S rims. M3 alite was the primary component of the MgO-doped clinkers, whereas the M1 type was stabilized by SO 3 ; these results were confirmed using seven characteristic windows of high-angle-resolution XRD patterns.