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Abstract

Most studies assume that fresh concrete is a Bingham fluid, but few studies precisely measure its Bingham constants, shear yield stress and viscosity, especially for normal fresh concrete. In stead of using commercial viscometer, this work developed a new experimental method and analytical procedure, based on the Stokes’ flow, for characterizing rheological properties of fluids. The experimental method developed here involved dragging a sphere submerged in the specimen fluid at a constant speed and measuring the resistance. Rheological properties of the specimen fluid can be calculated from the theoretical function correlating the drag velocity, drag force, and rheological properties of the fluid. Clay grout, fresh mortar and normal fresh concrete were tested. The measured Bingham constants were repeatable and stable, and importantly revealed that the clay grout and fresh mortar are Bingham fluids with very low viscosity, while normal fresh concrete is a Bingham fluid with rheological properties that depend on flow rate. This study also verifies that the shear stress required to start a concrete flow exceeds that required for maintaining it.

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