EFFECT OF VISCOSITY MODIFYING ADMIXTURES ON THE RHEOLOGICAL PROPERTIES AND STABILITY OF SELF CONSOLIDATING CEMENTITIOUS MATERIALS

Cement paste serves as the basis for the workability properties of selfcompacting concrete (SCC) and these properties could be assessed by self consolidating cementitious materials (SCCM). SCCMs have to be sufficiently fluid to ensure the fluidity of the SCC itself and sufficiently viscous to support the coarse aggregates. Viscosity modifying admixtures (VMAs) are water-soluble polymers that increase the viscosity of mixing water and enhance the ability of cement paste to retain its constituents in suspension. From a rheological point of view, the use of a VMA along with adequate superplasticizers (SPs) content enables to ensure high deformability and stability. Two VMAs in addition of constant polycarboxylic based SPs were used in this study. In this research, role of VMAs on the stability of SCCMs have been investigated. The paste measurements were conducted on empirical tests, namely Mini-slump, Marsh cone and Mezur test. These tests are performed on the 36 cement pastes. Bleeding and segregation were determined by Mezur test in 5, 10, 15 and 20 minutes. This paper reports test results leading to the recommendation of suitable water/cement (W/C) ratio, and amount of VMAs that can be used to achieve adequate viscosity which leads to stable cement paste. It is proved that the rheological properties of cement paste are mainly affected by the W/C ratio and other parameters have an indirect effect on rheological properties.