Title: Estimating Rheological Properties of Superplasticized Cement Paste at High Temperature and Prolonged Mixing Using Various Rheological Models and Oscillatory Rheology
Author(s): Samer Al Martini, Ahmad Khartabil, and Moncef L. Nehdi
Publication: Materials Journal
Appears on pages(s): 359-370
Keywords: cement paste; high temperature; mixing time; oscillatory rheology; plastic viscosity; rheological models; superplasticizer; yield stress
In this study, the rheological properties of cement pastes incorporating various superplasticizers and subjected to prolonged mixing at high temperatures were estimated using shear flow and oscillatory rheology tests. Various rheological models were employed to estimate the rheological parameters from shear flow curves. This study proposed an approach to determine the consistency index and flow behavior index in the Power Law, Herschel-Bulkley, and Casson models. The performance of the rheological models was evaluated by calculating the standard error for each model. The results show that the standard error depended on the model used, mixing time, temperature, and admixture dosage. There was a common, increasing trend of the standard error with increased mixing duration for all models investigated. The yield stress from oscillatory shear tests was estimated using the intersection between the viscous part of the oscillatory shear strain/stress curve and the oscillatory shear stress axis. At a low shear stress range, the oscillatory shear strain/stress curve of cement paste was characteristic of a linear elastic solid, while at a higher stress range, it was characteristic of a viscous liquid. It was found that the yield stress estimated from conventional flow curves using the rheological models was generally higher than the corresponding value estimated using the oscillatory rheology test. Moreover, the yield stress from the Casson and Herschel-Bulkley models exhibited the lowest percentage difference compared to that from the oscillatory rheology tests.