Properties of type K expensive cement of pure components II. Proposed mechanism of ettringite formation and expansion in unrestrained paste of pure expansive component

Abstract A model is proposed to account for the behaviour of unrestrained paste hydrated pure K expansive component, based on growth of a porous ettringite layer around the C4A3S grains, resulting in an expanding sphere. At the critical degree of hydration, αcr, first contact is formed between the expanding spheres and they start pushing against each other, causing expansion. The model accounts quantitatively for the course of expansion and variation in porosity upon hydration and the variations of these parameters with temperature, as well as for the pore size distribution.