APPLICATION OF SELECTIVE SI-29 ISOTOPIC ENRICHMENT TO STUDIES OF THE STRUCTURE OF CALCIUM SILICATE HYDRATE (C-S-H) GELS

Selective isotopic enrichment of SiO2 with Si-29 in a mixture with tricalcium silicate (C3S) has allowed the Si from this phase to be effectively labeled during the course of the hydration reaction, thus isolating its contribution to the reaction. A double Q(2) signal has been observed in Si-29 solid-state MAS NMR spectroscopy of C-S-H gels of relatively low Ca/Si ratio, prepared by hydration or by carbonation of a C3S paste. The origin of the weaker, downfield peak is discussed and tentatively attributed to bridging tetrahedra of a dreierkette silicate chain structure.