Ceramics-Silikáty 56 (4) 389-395 (2012)

HYDRATION MECHANISMS OF CALCIUM SULPHOALUMINATE C₄A₃S̄ , C₄AS̄ PHASE AND ACTIVE BELITE β-C₂S

H. El-Didamony, Kh. A. Khalil, M. Heikal, I. A. Ahmed 

Highly reactive belite and calcium sulphoaluminate as well as monosulphate mix were prepared from nano-materials at lower temperatures ~1250°C. The crystal size of these materials was 25, 16 and 27 nm as determined from the X-ray analysis. The sulphoaluminate belite cement is a recent type of cement prepared at lower temperature with good properties. The aim of the present work is to synthesize C₄A₃S̄, monosulphate mix C₄AS̄ and active belite β-C₂S. The hydration mechanism was studied by XRD and DSC techniques as well as by the determination of chemically combined water contents of cement pastes with curing time. The results reveal that ettringite is first formed hydrates in the monosulphate mix, which then converted into monosulphate hydrates. The results of DSC and XRD are in good agreement with those of combined water contents. On the other side, the rate of hydration of active belite increases linearly from 3 up to 90 days, whereas, the traditional belite hydrates increase with lower rate up to 90 days, due to the thermodynamic stability structure of traditional belite.

Keywords: Calcium sulphoaluminate (C₄A₃S̄ ), β-dicalsium silicate (active belite), Hydration characteristics, XRD and DSC