Effect of urea on the thixotropic behavior of mixtures containing calcium aluminate cement and portland cement

Abstract

This study investigates influence of urea utilization on the rheological and thixotropic properties of Portland and calcium aluminate cementitious system. In each cementitious system, a total of eight different paste mixtures were prepared with 2.5%, 5% and 10% replacement of cement weight with urea. Thixotropic behavior was evaluated using the step change and the loop methods. The use of urea in cementitious systems, independent of the type of cement, was found to result in a decrease in dynamic shear stress and viscosity values, in other words, an increase in flow performance. The addition of urea was observed to increase the formation of thixotropic structure, and this effect is more pronounced in Portland cement mixtures. The Herschel-Bulkley model is more consistent with the rheological data obtained in Portland cement mixtures. In Portland cement mixtures, the values of structural build-up are observed to be higher compared to the values of structural breakdown, while in calcium aluminate cement mixtures, the opposite has been observed. The viscosity after rest value decreased by 95% with the addition of 10% urea to the mixture containing Portland cement, and this value decreased by 76% with the addition of 10% urea to the mixture containing calcium alumina.