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Global hydration kinetics of tricalcium silicate cement
1Institut für Computeranwendungen I, Universität Stuttgart, Pfaffenwaldring 27, D-70569 Stuttgart, Germany.
Summary
This study reveals that tricalcium silicate hydration follows two distinct power laws, indicating an initial acceleration followed by a slowdown. This behavior is linked to hydrate catalysis and inhibition, suggesting a plate-like microstructure.
Area of Science:
- Materials Science
- Chemical Engineering
- Physical Chemistry
Background:
- Tricalcium silicate (C3S) is a primary component of Portland cement.
- Understanding its hydration kinetics is crucial for concrete performance.
- Previous models often simplify the complex reaction pathways.
Purpose of the Study:
- To re-evaluate hydration kinetics of tricalcium silicate pastes.
- To characterize the time-dependent evolution of hydrated and unhydrated silica.
- To propose a rate equation explaining the observed kinetic behavior.
Main Methods:
- Analysis of experimental measurements of tricalcium silicate paste hydration.
- Modeling the ratio of hydrated to unhydrated silica mole numbers using power laws.
- Interpretation of kinetic data using a global second-order rate equation.
Main Results:
- Hydration kinetics are described by two power laws: accelerated (ψ=5/2) for early times and parabolic (ψ=1/2) for later times.
- A crossover time (tx) of approximately 16 hours was identified.
- Hydrates were found to catalyze early hydration and inhibit later stages.
Conclusions:
- The observed kinetics support a second-order rate equation where hydrates act as catalysts and inhibitors.
- The exponents (ψ=5/2, ψ=1/2) suggest a plate-like hydrate microstructure.
- This aligns with experimental observations of cellular hydrate microstructures in C3S materials.