The hydration of tricalcium aluminate in Portland cement-related systems

In a recently published review article, experiments, simulations and derived theories for the hydration of tricalcium aluminate in Portland cement-related systems are summarised and further conclusions are drawn.

In recent years, the knowledge on tricalcium aluminate, its synthesis as well as new examination methods concerning relevant hydration mechanisms reached a higher quality and diversity, leading to a substantial gain in knowledge and an increasing number of publications. Image source: fotofrank (symbol image).

Highly reactive calcium sulfates lead to an earlier sulfate depletion, possibly due to their faster dissolution and consequently enhanced sulfate consumption by forming more ettringite instead of AFm. Sodium in solid solution decreases the crystal symmetry of tricalcium aluminate (Ca3Al2O6) and is released over-proportionally during dissolution. When reacting only with water, sodium in solid solution and in the pore solution decreases the dissolution.

Delayed hadration

At lower humidity, hydration starts with a delay, and the minimum humidity that allows a reaction depends on the overall composition of the system. Organic admixtures may interfere with the balance between aluminate phases and calcium sulfates thus disturbing the silicate reaction. The retardations of aluminate phases by sulfate and silicate phases by aluminate are likely due to surface sorption of ions suppressing the dissolution.

The review has been published in Cement and Concrete Research, Volume 168, June 2023.

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