Interactions between polymeric dispersants and calcium silicate hydrates. The Wulff shape of alumina. I. Modeling the kinetics of morphological evolution

• Published in: Journal of the American Ceramic Society 2000-10, Vol.83 (10), p.2556-2560
• Main Authors: Gartner, E, Geoffroy, G, Renou-Gonnord, M F, Faucon, P.,-, Popova, A
• Format: Article
• Language: English
• ISSN: 0002-7820

To better understand the mechanism of interaction between hydrating silicate-based cements and polymeric dispersants of the type used as 'superplasticizers' in modern construction concretes, two different types of polymeric dispersant were added (at concentrations of 1 and 10 g/L) during the synthesis of calcium silicate hydrate (C-S-H) via the 'pozzolanic reaction' in dilute slurries of lime and reactive silica, at Ca/Si ratios in the range of 0.66-1.50. Although both polymers gave degrees of adsorption of > 79% in all cases studied, no significant structural modifications of the resulting C-S-H products were observed via X-ray diffraction or exp 29 Si magic angle spinning- nuclear magnetic resonance. These results differ from recent work in which it was shown that similar types of polymer could intercalate into the interlayers of C-S-H that was made using an alternative process. It is suggested that the process by which the C-S-H is formed may have a strong influence on whether C-S-H can intercalate polymers. This observation is relevant to understanding the fate of such polymers in concrete. The rate at which fully facetted nonequilibrium shaped particles and pores approach their equilibrium (Wulff) shape via surface diffusion was modeled, and calculations relevant to alumina were performed to guide experimental studies. The modeling focuses on 2-D features, and considers initial particle/pore shape, size, surface energy anisotropy, and temperature (surface diffusivity) as variables. As expected, the most important parameters affecting the evolution times are the cross-sectional area (volume in 3-D) and the temperature through its effect on the surface diffusivity. Pores of micrometer size are predicted to reach near-equilibrium shapes in reasonable times at temperatures as low as 1600 deg C.