STUDIES ON RHEOLOGICAL PROPERTIES OF SUPERPLASTICISED PPC PASTE

Rheology is the science which deals with flow and deformation of matter under applied force. The study of rheological response of superplasticised PPC pastes subjected to a stepwise loading at a constant temperature using different flow models is presented here. Rheological tests are done in temperature controlled Coaxial Cylinder Viscometer (Brookfield DV-II) to determine the parameters which in turn describe the flow behaviour. Mix prepared at water-binder ratio of 0.37 using two brands Portland Pozzolana Cement (PPC) and Superplasticisers (SP) of four different families namely Polycarboxylate Ether, Sulphonated Melamine Formaldehyde, Sulphonated Naphthalene Formaldehyde and Lignosulphates were used for the study. The tests were done on 5 mixes in each superplasticiser, one on the optimum dosage obtained and the remaining were on the dosage values lower and higher than the optimum dosage. Optimum dosage of the superplasticiser was obtained from the empirical tests like mini slump test and marsh cone tests. Cement pastes were placed in the sample chamber of coaxial cylinder viscometer and shear stress produced when a known shear rate applied to the fluid through spindle is measured at a constant temperature of 27ºC. Two loading and unloading cycles were imposed by increasing, and later decreasing the shear rate. The response of downward curve of the second cycle is used for determining the rheological parameters. Rheological parameters obtained at constant test temperature by fitting the second cycle downward flow curves using Bingham model and Herschel Bulkley model are compared.