The role of topological disorder and heterogeneity on the dissolution kinetics of glasses

The quest for sustainable concrete has led to the search of materials with a low-carbon footprint, known as supplementary cementitious materials (SCMs), that can substitute ordinary Portland cement (OPC) as binder. The major bottleneck limiting the replacement of OPC by SCMs is the slower reactivity of the latter, which results in insufficient early-strength development of the cement paste. As a result, there is a pressing need for discovering or designing new, highly reactive SCM formulations. However, our understanding of the dissolution kinetics of SCMs, which are made of calcium aluminosilicate (CAS) amorphous phases arranged in complex morphologies, remains very limited. Here, we use kinetic Monte Carlo simulations on a model system of a 3-D SCM particle to systematically investigate the role of topological disorder and multiphase morphology on the far-from-equilibrium dissolution kinetics. We find an interesting complex interplay between the average topological disorder in the particle, which is correlated to the average activation barrier associated to the dissolution events, and the heterogeneous distribution of that topological disorder in the particle. For high average activation barriers (i.e., more crystalline SCMs), heterogeneity in the topological disorder slows down dissolution, which is in agreement with our theoretical expectations. However, for low average activation barriers, increased heterogeneity speeds up dissolution. We show that his non-trivial, counterintuitive behavior arises from the incongruent dissolution mechanism of these systems and the fact that dissolution is a non-equilibrium, path-dependent process. Our results provide fundamental insight into the fundamental mechanisms that govern the dissolution kinetics of complex disordered materials like SCMs.