Comb-shaped polymers as nanostructure modifiers of calcium silicate hydrate: a 29Si Solid-State NMR investigation

Calcium silicate hydrate gel (C–S–H) is the complex phase mostly responsible for the binding properties and the mechanical resistance of Portland cement. The clarification of the C–S–H nanostructure and how the presence of organic additives affects it is still an intriguing and not trivial task, especially due to C–S–H scarce crystallinity and intrinsic complexity. In this work, we exploited 29Si solid-state nuclear magnetic resonance (NMR) to investigate the effects of different comb-shaped superplasticizers on the silicate structure. The analysis of 29Si solid-state NMR spectra shows that the additives increase the degree of polymerization and hence the average length of the silicate chains in C–S–H. This finding correlates well with the increase of the globule dimensions estimated by means of small angle scattering techniques showing that the comb-shaped polymers are able to tune the overall dimension of the C–S–H globule. This effect is dependent on the molecular architecture of the superplasticizer and allows a molecular imprinting to the globular structure of the C–S–H gel.