Yield Stress of Mortars in Rotational and Oscillatory Shear Experiments Conducted Using A Ball Measuring System

Abstract

This study compared the flow curve fitting and oscillatory strain sweep methods to determine the yield stresses of Portland cement mortars using a ball measuring system (BMS). The tests were performed in two stages. In the first stage, the responses from a BMS with ball diameters of 8, 12, and 15 mm were compared to those from conventional cone-plate geometry with two different polymer dispersions. In the second stage, thirty-five mortars were prepared with 10 wt% of the cement replaced by silica fume. Five water-to-binder ratios and seven concentrations of a polycarboxylate-based superplasticizer were selected. An 8-mm diameter ball was selected for use in mortar production due to the smaller drag that it produced. The results indicated an increase in the linear viscoelastic region due to a reduction in the water-to-binder ratio and/or an increase in the superplasticizer concentration. In oscillatory tests, the dynamic yield stress was related to the stability of the cement paste and the strengths of the internal links between the cement particles. The flow and Herschel-Bulkley yield stresses result were not statistically different. Therefore, flow stress calculations could be carried out using either of these methods. An amplitude sweep test performed using the BMS may be an alternative method of studying the rheology of cement-based materials.

Keywords

• mortar
• yield stress
• crossover modulus
• viscoelastic linear region
• flow behavior