Si-29 and O-17 NMR investigation of the structure of some crystalline calcium silicate hydrates

This paper presents the results of a systematic investigation of the structure of O-17-enriched, hydrothermally synthesized 1.1-nm tobermorite, 1.4-nm tobermorite, jennite calciochondrodite, xonotlite, and hillebrandite, using Si-29 magic angle spinning (MAS) NMR, H-1-Si-29 cross-polarization magic angle spinning (CPMAS) NMR, and O-17 MAS NMR. The O-17 and most of the H-1-Si-29 CPMAS results are the first reported for these phases. Six types of oxygen sites were observed in tobermorite and jennite, including both Si-OH and Ca-OH linkages. The structure of 1.4-nm tobermorite is similar to that of 1.1-nm tobermorite with about 26% of the Ca2+'s in the interlayers. The results support the proposed jennite structure in which silicate chains and rows of OH- groups alternately occur along the CaO layers [1]. Jennite contains long, single silicate chains similar to those in 1.4-nm tobermorite, with Si-OH sites primarily occurring on bridging tetrahedra, and there seems to be no interlayer Ca2+'s. Although the Si sites in xonotlite and calciochondrodite cross-polarize well, neither contains Si-OH linkages.