How to increase the hydration degree of CA — The influence of CA particle fineness

It is shown that the hydration degree of CA is directly dependent on the fineness of CA-particles. Finer particles lead to an increased degree of hydration and also an increased hydration rate.The reaction of a sample with mainly coarse particles of CA (d50 = 50 μm) is characterized by a low hydration rate and only 34 rel.-% of CA dissolved after 22 h. Whereas in a very fine CA-sample (d50 = 4 μm) hydration starts delayed but then shows the highest hydration rate and a dissolution of 62 rel.-% CA. The behaviour is explained by the coverage of CA-particles with a dense hydrate layer of C2AHx and AHx. This reacted CA-rim is supposed to have the same thickness for different sized CA-particles. Optimization of Gauss distribution curves, which were applied to simulate a more realistic particle size distribution, leads to a reacted rim thickness of 1.3 μm until reaction is stopped.