Abstract
The concurrent dissolution and early hydration of tricalcium aluminate (C(3)A) and tetracalcium aluminoferrite (C(4)AF) critically govern early-stage reaction dynamics in Portland cement systems. However, their mutual kinetic interactions during reaction, particularly sulfate-dependent modulation mechanisms, remain poorly understood. Using in-situ digital holographic microscopy (DHM), this study resolved their interaction mechanisms during co-dissolution in aqueous and sulfate-bearing environments. Results reveal asymmetric modulation: while C(4)AF's dissolution exhibited limited sensitivity to C(3)A's presence, C(3)A's kinetics were profoundly altered by C(4)AF through sulfate-concentration-dependent pathways, which originated from two competing C(4)AF-mediated mechanisms: (1) suppression via common-ion effects, and (2) acceleration through competitive sulfate species adsorption. These mechanistic insights would provide a roadmap for optimizing cementitious materials through optimized reaction pathways.