Effect of Different Molecular Weights and Chemical Composition of Superplasticizers on the Structural Build-up of Cement Paste Using Dynamic Oscillatory Rheology

摘要

Two polycarboxylate ether (PCE) superplasticizers with different molar masses and functionalities were studied in relation to their strain and time-dependant Theological properties.The effect of dosage on cement paste fluidity and structural-build up was of particular interest.Through size exclusion chromatography (SEC) the relative molar mass and polydispersity index (PDI) was determined.Superplasticizer A (SP-A) was found to be three times the molar mass of superplasticizer B (SP-B).The dosage limitations were then determined through a spread flow test.The SP-B,with a lower molar mass,and a backbone functionality of a methacrylate-ester,began to flow at higher dosages and with relatively small changes in dosage,a large impact on the fluidity was notable.Dynamic oscillatory rheology was used to determine structural build-up,as a non-destructive method.The structural build-up of cement paste is a time-dependent phenomenon therefore a time sweep was done.A constant strain and angular frequency,within the linear viscoelastic regime (LVE),was used.The LVE was determined through a series of oscillatory strain sweeps for cement pastes with and without SP-A and B.Thereafter the rate of rigidification (G_(ridge)) and percolation time (t_(perc)) as a function of hydration time was investigated.