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 (& UDelta;G*) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or 1 over bar 00, 010 or 01 over bar 0, 1 over bar 10 or 11 over bar 0, and 001 or 001 over bar ) 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 01 over bar 0 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 01 over bar 0) was computed to be 1.0443 mol/(s cm(2)); however, 0.0032 mol/(s cm(2)) for 1 over bar 10 or 11 over bar 0, 2.672 x 10(-7) mol/(s cm(2)) for 001 or 001 over bar , and 0.31 x 10(-16) mol/(s cm(2)) for 100 or 1 over bar 00 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.

Automated summary

This study investigates the dissolution time and morphology changes of a hexagonal platelet portlandite crystal using an atomistic kinetic Monte Carlo (KMC) upscaling approach. Results show that the dissolution process initially occurs from the edges, sides, and facets of the crystal morphology. The dissolution rates vary significantly among different facets, highlighting the importance of crystallographic orientation.