Carbonation of calcium sulfoaluminate belite binder: mechanism and its implication on properties

Calcium sulfoaluminate belite (CSAB) binder is an alternative low CO₂ binder. CSAB cement has ye’elimite as the primary clinker phase which hydrates to form monosulfate or ettringite as the main hydration product. The hydration and mechanical characteristics of CSAB cement and PC-CSAB blended cement have been reported in several studies; however, studies on the durability characteristics such as carbonation are limited. This study focuses on evaluating the microstructural and mechanical alterations due to carbonation in a CSAB binder system and understanding the underlying mechanism of development of the carbonation front. CSAB binder was found to carbonate rapidly compared to PC binder, accompanied by a reduction in compressive strength. This was attributed to the increase in the pore volume due to the carbonation of the ettringite-rich microstructure, facilitating further ingress of CO₂ into the microstructure. The rate of carbonation in CSAB binders diverged significantly from the square root of time model used for PC binders.