Highly Reactive β‐Dicalcium Silicate: II, Hydration Behavior at 25°C Followed by ²⁹ Si Nuclear Magnetic Resonance

Abstract

The hydration behavior at 25°C of highly reactive β‐dicalcium silicate synthesized from hillebrandite (Ca 2 (SiO 3 )(OH) 2 ) was studied over a period of 7 to 224 d using 29 Si magic‐angle spinning nuclear magnetic resonance (MAS NMR). The hydration product, C‐S‐H, contains Q 2 and Q 1 silicate tetrahedra, the chemical shifts of which are independent of the water/solid (w/s) ratio and curing time. Until the reaction is completed, the amounts of Q 1 and Q 2 formed are independent of the w/s ratio, being determined only by the degree of reaction. The ratio Q 2 /Q 1 increases as the reaction progresses and as the curing time becomes longer. From the values of Q 2 /Q 1 , it appears that the hydrate is a mixture of dimers and short single‐chain polymers. The Ca/Si ratio of the hydrate is high, taking values close to 2.0, but the Ca/Si ratio does not influence the Q 2 /Q 1 ratio. It was also found that the NMR peak intensities allow quantitative assessment similar to XRD.