Developing Falling-Ball Viscometer for Highly Flowable Cement-Based Materials

Abstract

Northwestern University's Center for Advanced Cement-Based Materials designed and developed a scale, suspended steel ball, and spring based falling-ball viscometer to measure cement-based materials' rheological properties. By investigating the relationship between falling-ball velocity and drag force exerted on ball surface, the viscometer can determine a fluid's yield stress and plastic viscosity. The authors discuss a two-step study. The first step investigated paste properties when water-cement ratio was the same but high-range water-reducing admixtures and viscosity-modifying admixture contents varied. The second stage researched the same paste matrix with varied sand content mortars. Study results showed that mixture composition variation changes could be measured by the falling-ball viscometer. The mini-cone slump test determined slump flow diameter, which corresponded very well to measured yield stress. Viscometer application to high fluidity concretes, such as self-consolidating concrete, has high potential.