Calculation of plastic viscosity of concrete mixture using the modified empirical formula

摘要

Nowadays various types of viscometers are being designed to measure the rheological properties of cement paste and fresh concrete. Most of them are very expensive and require specific knowledge about their usage. Then in practice usually the empirical formulas are used to calculate the main rheological properties - yield stress (Pa) and plastic viscosity (Pas). Therefore, in the literature, there are some formulas which can't be used to calculate analytically plastic viscosity of concrete mixture, e.g. it cannot estimate the influence of different chemical admixture on plastic viscosity of concrete. The paper focuses on the modification of the empirical formula to calculate the plastic viscosity of fresh concrete mixture. In this paper the way of viscosity formula modification was described. For an empirical formula modification, the coefficients which describe the influence of different chemical admixture on plastic viscosity of concrete mixture were used. Coefficients K_(calc). were calculated as a ratio between different viscosity values of cement pastes obtained without and with certain chemical admixtures. Viscosity of cement paste was obtained by using rotational viscometer Rheotest RN4. Coefficients describe the change in cement pastes viscosity when adding different type (superplasticizer, viscosity modifying agent, air-entraining agent and air voids removing agent) and amount of chemical admixture.