# Dissolution and Early Hydration Interaction of C3A-C4AF Polyphase in Water and Aqueous Sulfate Solutions

## TL;DR

This study explores how two cement components interact during early hydration, revealing how sulfate affects their dissolution rates.

## Contribution

The paper identifies two competing mechanisms by which C4AF modulates C3A dissolution in sulfate environments.

## Key findings

- C4AF dissolution is minimally affected by C3A presence.
- C3A dissolution is strongly influenced by C4AF through sulfate-dependent pathways.
- Two mechanisms—common-ion suppression and sulfate adsorption acceleration—compete during dissolution.

## Abstract

The concurrent dissolution and early hydration of tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) 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 C4AF’s dissolution exhibited limited sensitivity to C3A’s presence, C3A’s kinetics were profoundly altered by C4AF through sulfate-concentration-dependent pathways, which originated from two competing C4AF-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.