Dissolution of Portlandite in Pure Water: Part 2 Atomistic Kinetic Monte Carlo (KMC) Approach

Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology changes of a hexagonal platelet portlandite crystal. First, the atomistic rate constants of individual Ca dissolution events are computed by a transition state theory equation based on inputs of the computed activation energies (ΔG*) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or [Formula: see text] , 010 or 0 [Formula: see text] 0, [Formula: see text] or [Formula: see text] , and 001 or 00 [Formula: see text]) are considered, resulting in a total of 16 different atomistic event scenarios. Results of the upscaled KMC simulations demonstrate that dissolution process initially takes place from edges, sides, and facets of 010 or 0 [Formula: see text] 0 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 0 [Formula: see text]) was computed to be 1.0443 mol/(s cm(2)); however, 0.0032 mol/(s cm(2)) for [Formula: see text] or [Formula: see text] , 2.672 × 10(−7) mol/(s cm(2)) for 001 or 00 [Formula: see text] , and 0.31 × 10(−16) mol/(s cm(2)) for 100 or [Formula: see text] were represented in a decreasing order for less reactive facets. Obtained upscaled dissolution rates between each facet resulted in a huge (16 orders of magnitude) difference, reflecting the importance of crystallographic orientation of the exposed facets.