Synthesis of dispersing agents from starch – Influence on rheological properties and early age hydration of OPC

Abstract

This study deals with the influence and effectivity of synthesized starch-based superplasticizers on rheological behaviour of cement pastes and on cement hydration. By varying molecular parameters, like molecular weight and the amount of introduced anionic charges, key parameters which induce thickening or liquefying behaviour in cement pastes were identified. Cement hydration was monitored by isothermal calorimetry, ultrasonic measurements and conductivity experiments. The investigations were supplemented by adsorption measurements by the phenol-sulphuric acid method. Results clearly show that low molecular weights and anionic charges in the molecular structure are necessary to create superplasticizers from starch. Also, the amount of anionic charges implemented in the molecular structure by chemical modification is a key parameter for a high dispersing performance. Furthermore, the starch-based superplasticizers delay the hydration of cement pastes, because of adsorption on cement surface, especially on the first hydration products.