Cement-polymer and clay-polymer nano- and meso-composites: spotting the difference

Abstract

Calcium silicate hydrate (C-S-H), the most important reaction product of Portland cement with water, is a layered lattice silicate which has much in common with smectite clays. Both materials may be synthesised (C-S-H) or found in nature (smectites) in the form of particles which are stacks of negatively charged nanometre-thick platelets separated by water molecules and charge-compensating cations. Smectite clays are well known for their ability to intercalate molecular species including polymers, to “swell” in a remarkable variety of solvents and to form nano-composites with polymers in which total delamination may eventually be obtained. In this work, we explore the possibility of intercalating cationic, anionic and neutral water-soluble polymers in C-S-H. Contrary to recent reports, no clear signs for intercalation of the macromolecules were observed. Nevertheless, the significant amount of polymer retained by the silicate suggests that the composite materials formed may be considered as meso-composites in which the individual solid units are not the individual C-S-H sheets but crystallites thereof. The localisation of electric charges and the strong Coulombic forces acting in cement hydrates are thought to be responsible for this difference.