The study on the dispersing mechanism of starch sulfonate as a water-reducing agent for cement

Many water-reducing agents are environmentally unacceptable and non-renewable. As environment-friendly and renewable organic resource, starch has been used to synthesize starch sulfortate (SS). In this paper, the adsorption characteristics of SS on Portland cement particles were investigated by measuring zeta potentials, X-ray photo spectroscopy and UV-visible adsorption and its effects on the fluidity of cement paste were studied in comparison with traditional naphthalene sulfonated formaldehyde condensates (FDN) whose dispersion ability mainly depends on electrostatic repulsive forces. The results indicate the adsorption isotherm of SS conforms to Langmuir-type adsorption and the adsorption conformation of SS is dendritic due to its molecular structure. The adsorption layer of SS is much thicker than FDN. The dispersion capacity of SS mainly comes from steric hindrance effects rather than electrostatic repulsive forces. The dispersions stabilized by steric hindrance have better fluidity at lower adsorption amount and higher stability than those stabilized by electrostatic repulsive forces. (C) 2007 Published by Elsevier Ltd.