Rheological behaviors of fresh cement pastes with polycarboxylate superplasticizer

Abstract

The rheological behaviors of fresh cement paste with polycarboxylate superplasticizer were systematically investigated. Influential factors including superplasticizer to cement ratio (Sp/C), water to cement ratio (w/c), temperature, and time were discussed. Fresh cement pastes with Sp/Cs in the range of 0 to 2.0% and varied W/Cs from 0.25 to 0.5 were prepared and tested at 0, 20 and 40 °C, respectively. Flowability and rheological tests on cement pastes were conducted to characterize the development of the rheological behavior of fresh cement pastes over time. The exprimental results indicate that the initial flowability and flowability retention over shelf time increase with the growth in superplasticizer dosage due to the plasticizing effect and retardation effect of superplasticizer. Higher temperature usually leads to a sharper drop in initial flowability and flowability retention. However, for the cement paste with high Sp/C or w/c, the flowability is slightly affected by temperature. Yield stress and plastic viscosity show similar variation trends to the flowability under the abovementioned influential factors at low Sp/C. In the case of high Sp/C, yield stress and plastic viscosity start to decline over shelf time and the decreasing rate descends at elevated temperature. Moreover, two equations to roughly predict yield stress and plastic viscosity of the fresh cement pastes incorporating Sp/C, w/c, temperature and time are developed on the basis of the existing models, in which experimental constants can be extracted from a database created by the rheological test results.