Mechanism of the hydration of 3CaO, Al₂O

Abstract

Abstract Hydration of pastes of 3CaO, Al 2 O 3 with water shows two different heat effects: (1) on the first contact of the 3CaO, Al 2 O 3 particles with water, (2) when crystallisation of the ultimate hydration product, the cubic 3CaO, Al 2 O 3 ,6H 2 O, from the intermediate hexagonal calcium hydroaluminates becomes more pronounced. Addition of 3CaO, Al 2 O 3 ,6H 2 O shifts the second peak to earlier times and accelerates the hydration. The results appear to be at variance with a mechanism involving particle disintegration through crystallisation of hydration products in surface cracks, as a cause for the second peak. The results suggest that water transport through a layer of hydration product is the rate‐determining step, and that the layer is likely to be removed partly by being dissolved when 3CaO, Al 2 O 3 ,6H 2 O is formed predominantly.