THE COMPOSITIONAL AND MOLECULAR CHARACTER OF THE CALCIUM SILICATE HYDRATES FORMED IN THE PASTE HYDRATION OF 3CAO.SIO2

Transmission electron microscopy has been used to determine the composition and characterize the molecular structure of the early calcium silicate hydrates formed in the paste hydration of 3CaO . SiO2. The initial surface hydrates were found to have a wide range of CaO/SiO2 compositions, consistent with the rapid and variable rate of dissolution of Ca2+ ions from only specific reactive surface sites. The very early surface hydrates appear disordered on a 1 nm scale. At later ages these become microheterogeneous, with more structurally ordered sheet-like fragments and regions developing within the disordered regions. Discrete 3 nm long and 1 nm thick fragments and more structurally ordered assemblies of these were observed. The basic molecular core structure was found to be a 1 nm thick sheet consisting of a protonated CaO(x) polyhedral layer sandwiched between short-chain silicate groups. In these paste hydrates, this layer extends for only 3 nm before disordering recurs.