William B. Ledbetter

An Investigation Of A High Speed Shear Mixer On Selected Pastes And Mortars

The influence of shear mixing on selected properties of cement pastes and mortars was investigated by preparing specimens using an ordinary paddle mixer and a high speed shear mixer. The results appear to indicate that shear mixing influences the bond between paste and aggregate, particularily at low water:cement ratios. The properties of hardened cement paste did not change markedly as a result of high speed shear mixing used in this initial study.

Prediction of mortar-cube strength from cement characteristics

Abstract A model was developed to predict portland cement mortar-cube strengths at any age from one to 28 days with consistently high accuracy, based on a linear regression of selected physical and chemical characteristics routinely obtained in the cement laboratory. Random differences between model predictions and measured mortar-cube strengths appeared at all ages, but declined in magnitude with increasing age. Data “clustering” at given test ages resulted in low predictive capability of the model until it was “corrected” through a time-sequence dynamic correction procedure. The final model is: f′t = a(C3S)+b(C2S)+c(C3A+1.125{SO3})+d(C4AF)+e(SO3) + f(Blaine)+g(lnWC′) + Co.

ON THE GENERATION OF HEAT DURING THE MIXING OF CEMENT PASTES

Abstract A substantial amount of heat is generated during high-speed shear mixing of low water/cement ratio pastes (w/c = 0.24). It was found that the major source of this heat is mechanical friction. Under constant temperature conditions, no evidence was found to suggest that the degree of hydration is greater after high-speed shear mixing than after typical low-speed paddle mixing for the same period of time. Whether or not the temperature is controlled, shear mixing reduces the apparent viscosity of pastes having a low water/cement ratio, as compared with pastes from paddle mixing.