A 29Si MAS NMR study of modified C–S–H nanostructures

The sustainability of cement-based materials is a core technical issue of national importance. The serviceability of the concrete infrastructure, especially bridges, has recently received considerable media attention. Concurrently, the nanoscience of cements has emerged as a new discipline with the potential to positively manipulate the nanostructure of calcium silicate hydrate (C–S–H) in order to achieve sustainability objectives. Organic/inorganic C–S–H nanocomposites are being developed to enhance durability and long-term engineering behavior. Results of a 29Si MAS NMR study of phase pure C–S–H (prepared with C/S ratios 0.6–1.6) modified by interaction with hexadecyltrimethyl ammonium (HDTMA), methylene blue (MB), polyethylene glycol (PEG), polyvinylalcohol (PVA) and polyacrylic acid (PAA) are reported. It is apparent that the degree of silica polymerization is affected by the presence of the various organic molecules and the C/S ratio of the C–S–H. Possible mechanisms responsible for this effect are described. The implications of these nanostructural changes for sustainability are discussed. It is suggested that the interaction of polymers with the nanostructure of C–S–H that increases silicate polymerization may improve volume stability and promote mechanical properties of such systems. The resistance of polymer-modified C–S–H systems in chemically aggressive environments is likely to be increased as the defect sites in the silicate structure are eliminated by the presence of polymer molecules.