Journal
CEMENT AND CONCRETE RESEARCH
Volume 157, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cemconres.2022.106833
Keywords
Dicalcium silicate; Dissolution; Thermodynamics; Kinetics; Atomistic simulations; Rare event sampling
Funding
- Na-tional Science Fund for Distinguished Young Scholars [51925205]
- National Science Fund for Distinguished Young Scholars [51925205]
- China Scholarship Council [51925205]
- U.S. Department of Energy (DOE) , Office of Science, Office of Basic Energy Sciences (BES) , Chemical Sciences, Geosciences, and Biosciences Division through its Geosciences program at the University of California Irvine through an Early Career award [201906950033]
- U.S. National Science Foundation [DE-SC0022301]
- [CMMI-2103125]
- U.S. Department of Energy (DOE) [DE-SC0022301] Funding Source: U.S. Department of Energy (DOE)
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Low-temperature cement manufacturing attracts attention for its low environmental impact, but slow hydration kinetics affects early-age strength development. This study uses rare event sampling techniques to uncover the mechanism of calcium ion dissolution from a kink site, and calculates the rate and equilibrium constants for each reaction step.
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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