Interactions between calcium silicate hydrate (C-S-H) and calcium chloride, bromide and nitrate

The interaction between C-S-H and anions, especially chloride, is already well documented. However, the conclusions vary from one author to another and a comparison of the obtained data is not always possible. Thus, this study aims to clarify this phenomenon and extend it to the case of bromide and nitrate. For this matter, a new analytical method has been developed in order to make the measurement directly in synthetic C-S-H suspensions, i.e. without any filtration, after calcium salt addition. Various parameters have been taken into account: the anion type and concentration, the Ca/Si of the C-S-H particles (ranging from 0.8 to 1.42) and the incorporation of aluminum inside the C-S-H structure. It has been found that there is no specific adsorption of chloride, bromide or nitrate by C-S-H. Calcium adsorption, which has been detected and measured, is limited, whatever the initial Ca/Si, and the presence of aluminum does not have any influence on it.