The IBB rheometer (Beaupre and Mindness 1994; Ferraris and Brower 2001; Bartos, Sonebi, and Tamimi 2002) is a modification of the Tattersall two-point device. Although the IBB rheometer was originally developed to measure the rheology of wet-mix shotcrete, it has been successfully used on a wide range of concretes, from concretes with a slump of 20 mm to self-compacting
concretes.
The device consists of a rotating impeller inserted into a fixed cylindrical container. When testing concrete, a fixed container with dimensions 360 mm by 250 mm is used. A smaller container with dimensions 230 mm by 180 mm can be used for mortars. A computer controlled DC motor turns an H-shaped impeller capable of rotating either in a planetary motion or in an axial rotation. For concrete, a 50 mm gap is left between the impeller and the sides and bottom of the container. When the mortar setup is used, a 25 mm gap exists between the impeller and the container. Based on these dimensions, the maximum aggregate size is 25 mm for concrete samples and 12 mm for mortar samples.
A load cell measures the reaction torque from the impeller while a tachometer measures the impeller’s rotation speed. Like the Tattersall two-point device, the linear relationship between torque and speed is defined by the slope h and the zero speed intercept g, which are related to plastic viscosity and yield stress, respectively. The values of g and h are calculated automatically by the computer and displayed at the end of the test. However, g is reported in terms of N-m (not the yield stress unit of Pa) and h is given in terms of N-m-s (not the plastic viscosity unit of Pa-s).
A portable version of the IBB has been developed. The device is based on the same design as the original IBB, just on a smaller scale. The portable IBB is constructed on an aluminum frame and includes wheels for easy transport.
Advantages:
• The device measures yield stress and plastic viscosity.
• The operation of the device is automated.
• The device is applicable to a wide range of concrete workability.
• The device is self-calibrating.
Disadvantages:
• The results for yield stress and plastic viscosity are not given in terms of Pa and Pa-s, respectively.
• The device, in its current form, is too large for field use. The volume of concrete required for the test is larger than for most other rheometers.
• Like the Tattersall two-point device, segregation can occur over the duration of the test, even when the particular concrete mix would not be susceptible to segregation in actual placement conditions.
IBB Rheometer
