Silicon‐29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates

The reaction products formed in a series of fully “equilibrated,” roomtemperature‐hydrated, fumed colloidal silica plus lime water mixtures were examined using 29 Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally distinct calcium silicate hydrate (C‐S‐H) phases exist in the system CaO–SiO 2 –H 2 O. The more silica‐rich C‐S‐H (Ca/Si = 0.65 to 1.0) consists predominantly of long chains of silica tetrahedra (Q 2 middle units) similar to those found in 1.4‐nm tobermorite. The studied more lime‐rich C‐S‐H (Ca / Si = 1.1 to 1.3) consists of a mixture of dimer (Q 1 ) and shorter chains (Q 1 end units and Q 2 middle units) similar to that reported for synthetic jennite. No monomer units (Q 0 ) were detected.