Application of ²⁹Si Homonuclear and ¹H−²⁹Si Heteronuclear NMR Correlation to Structural Studies of Calcium Silicate Hydrates

Abstract

Structural characterization of calcium silicate hydrate (C-S-H) is of major importance, as it is the main constituent of Portland cement and is responsible for its principal cohesion and durability properties. In this paper we apply homonuclear and heteronuclear solid-state NMR methods for the investigation of C-S-H. We use double quantum homonuclear 29Si−29Si correlation using the BAck to BAck recoupling scheme to gain information about connectivity between silicates and 2D 1H−29Si HETeronuclear chemical shift CORelation (HETCOR) to characterize the proton environment of the silicate chains. Our observations are in agreement with the tobermorite model and with previous results, but we get evidence of a continuous decrease of the silicate chain length with increasing Ca/Si ratio rather than a bimodal distribution of chain length.

Incorporation of aluminium in calcium-silicate-hydrates

“…Previous studies assigned the different environments (e.g. [4,7,11,14,40,41]) as the end of chain Q 1 at − 79.4 ppm, the bridging silica Q 2 b at − 83.4 ppm within the "dreierketten", the pairing site Q 2 p at −85.3 ppm occurring in synthetic C-S-H and a bridging tetrahedra connected to another bridging silica tetrahedra by hydrogen bonding, Q 2 u at 88.5 ppm [27,42,43]. At Al/ Si = 0.2, in addition to the Q 2 p the presence of stratlingite leads to a signal at −85.6 ppm [44].…”

Impact of carbonation on unsaturated water transport properties of cement-based materials

“…29 Si Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) was used to probe the effect of carbonation on the C-S-H structure as commonly done [45,[48][49][50][51]. We did not use 13 C NMR because it was found difficult to distinguish one calcium carbonate from the others [52].…”

“…Morandeau [12,13] conducted similar experiments using CEM I pastes with or without fly ash (using 10% of CO 2 ). The pore volume of the CEM I pastes was almost uniformly Cement and Concrete Research 74 (2015) [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] reduced over the whole pore size distribution whereas a significant coarsening was obtained for pastes containing fly ash.…”

NMR research on cement clinker and its structures in early age hydration

“…Up to hydration for seven days, the trimeric Q 2 showed in a single structure, and hydration of samples for seven days was more complete than that of being hydrated for three days. If the hydration system contains the structures of Q 1 and Q 2 according to the formula [30] , it is deduced that the value of the integrated chain length (CL) is 2.7. If the Q 2 structure amount is 25%, the value of the integrated chain length (CL) is 3.0.…”

“…In different hydration stages, C-S-H formation, the microstructure of cement pastes with various silicate tetrahedron and their contents including the chain length and hydration rate of silicate tetrahedron could be characterized by NMR. The silicate tetrahedron structures were clearly detected in Q 0 -Q 4 fi ve styles [28][29][30][31][32][33][34] . Common phases(C 3 S, C 2 S, C 3 A and C 3 AF) in clinkers and cements were detected in the previous works [2] .…”