Understanding Surface Interfacial Phenomena During Tricalcium Silicate Dissolution From TEM and XRR

ABSTRACT Understanding the dissolution mechanism of tricalcium silicate (C 3 S) is essential for interpreting its reactivity in cementitious systems. While the dissolution mechanism of C 3 S has been considered to follow the classical leached‐layer model, the mechanism has also been proposed to occur through the coupled interfacial dissolution–reprecipitation (CIDR) pathway, which has been demonstrated for other silicate minerals. In this work, dissolved surfaces of C 3 S were examined using transmission electron microscopy (TEM) and X‐ray reflectivity (XRR) to distinguish between these competing dissolution mechanisms. XRR measurements of polycrystalline C 3 S indicated changes in near‐surface density following dissolution; however, the polycrystalline nature of the specimens prevented definitive attribution to either mechanism. In contrast, TEM imaging identified a sharp, well‐defined boundary between the crystalline C 3 S and an amorphous reaction layer, which can be indicative of CIDR. The precipitated amorphous silica‐rich surface layers were passivating and non‐passivating depending on the crystallographic orientation of the grains, which could influence the dissolution rates of C 3 S. These results collectively suggest that C 3 S dissolution is more consistent with the CIDR mechanism, although further experiments are required to confirm the atomistic exchange associated with this phenomenon.