The CEMAGREF-IMG (Ferraris and Brower 2001) is a large coaxial-cylinders rheometer originally developed to measure mud-flow rheology, but which has also been used to measure concrete rheology. Only one prototype of the device exists.
Since the CEMAGREF-IMG was not initially intended to measure the rheology of concrete, it is significantly larger than other rheometers. In fact, the large size of the device makes it impractical for measuring concrete. The outer cylinder is 120 cm in diameter and 90 cm tall, while the inner cylinder is 76 cm in diameter. The rheometer holds 500 liters of concrete and is mounted on a trailer. The inner cylinder rotates and measures torque while the outer cylinder remains stationary. Blades on the outer cylinder and a metallic grid on the inner cylinder reduce concrete slippage. Since the inner cylinder is mounted within the outer cylinder from the bottom instead of from the top, a rubber seal is provided at the base of the inner cylinder to ensure that all concrete remains within the gap between the cylinders. The torque on the inner cylinder at various rotation speeds is logged and used to calculate yield stress and plastic viscosity.
Although the large dimensions of the CEMAGREF-IMG allow the testing of concrete mixtures with large maximum aggregate sizes, the ratio of the outer radius to the inner radius is too large. As a result, plug flow occurs as the concrete near the inner cylinder is sheared while the shear stress applied to the concrete near the outer cylinder is insufficient to overcome the yield stress
of the concrete. The large size of the CEMAGREF-IMG also makes the device impractical to transport.
Advantages:
• The device measures yield stress and plastic viscosity.
• The size of the device accommodates large maximum aggregate sizes.
Disadvantages:
• The device was not originally designed to measure concrete and is too large for common field use.
• The geometry of the device should be improved to more accurately measure concrete rheology.
• The seals at the bottom of the inner cylinder must be replaced periodically and must be accounted for in the device’s calibration.
