Atomistic thermodynamics and kinetics of dicalcium silicate dissolution

Y Tao and S Zare and FZ Wang and MJA Qomi, CEMENT AND CONCRETE RESEARCH, 157, 106833 (2022).

DOI: 10.1016/j.cemconres.2022.106833

Low-temperature cement manufacturing has garnered academic and industrial attention for its low environmental footprints. However, the sluggish hydration kinetics of the resultant cement affects their early- age strength development. This motivates fundamental studies to unravel the mechanistic picture of the dissolution process and discover science- informed pathways to accelerate hydration. Standard atomistic simulations seldomly exceed a microsecond making them impractical to study slow dissolution processes. Here, using rare event sampling techniques, we provide the mechanistic picture of Ca2+ ion dissolution from a kink site on the dicalcium silicate surface. The Ca2+ ion dissolution is comprised of two sequential stages: breaking restraints from the kink sites to form a ledge adatom and detaching from the ledge/terrace adatom sites into the solution. The first and second stages feature free energy barriers of -63 kJ/mol and - 29 kJ/mol respectively, making the first stage the rate-limiting step of the entire Ca2+ dissolution kinetics. Using the reactive flux method, the rate and equilibrium constants for each reaction step are calculated, which yield the Ca2+ ion activity of -1.03 x 10-5. The diffusion calculations indicate that the surface effects lower the self-diffusion coefficient of Ca2+ ions at the solid-water interface.

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