Improvement of acid resistance of calcium silicate hydrate by thermal treatment

The following conclusions were obtained from the examinations of the acid resistance of calcium silicate hydrate. (1) The 1.1-nm tobermorite was formed from the batch mixture with a Ca/Si molar ratio of 0.6. Xonotlite was formed from the batch mixture with a Ca/Si molar ratio of 1.0. (2) For the sample prepared from a Ca/Si molar ratio of 1.0 in a batch mixture, beta-wollastonitc was formed by thermal treatment as the transition phase, and it was significantly dissolved in a hydrochloric acid solution. (3) For the sample prepared from a Ca/Si molar ratio of 0.6 in a batch mixture, beta-wollastonite was formed by thermal treatment above 1000 degreesC, but the dissolved amount of this sample by acid treatment was small and left the original morphology. It was suggested that excess silica content was deposited on surface during the thermal transition from the 1.1-nm tobermorite to beta-wollastonite. The deposited silica content significantly improved the acid resistance of beta-wollastonite due to the surface coating with a silica layer. (C) 2004 Elsevier Ltd. All rights reserved.