Concrete Workability

Wigmore Consistometer

The LCL flow test (Bartos 1992; Ferraris 1999; Bartos, Sonebi and Tamimi 2002) is very similar to the Angles flow box test. The test is suitable for concretes with low and moderate workability and is not appropriate for concretes with very low or very high workability. The device consists of a 150 mm by 600 mm rectangular box with a height of 150 mm. An external vibrator is attached to one end. A triangular wedge holds uncompacted concrete in the opposite end of the box. Rubber supports beneath the box isolate the box and absorb vibrations. To start the test, the wedge is removed and the vibrator is started. The time for concrete to spread to the other end of the box and fill to a line marked on the side of the box is measured. The results of the LCL flow test are related to plastic viscosity. Further, yield stress could be determined by slowly increasing the amplitude of vibration until the concrete begins to flow. Although the test provides a direct and usable result, the device must be calibrated using a standard aggregate and a standard mix design in order to interpret the results further. The difficulty in determining the endpoint of the test reduces the precision of the test results. Two sizes of the device exist: one for normal concrete and another for mortars and concretes with maximum aggregate size less than 12.5 mm. The larger device requires 35 liters of concrete.

Advantages:
• The LCL flow test is a dynamic test, capable of measuring values related to both yield stress and plastic viscosity.
• The test partially represents actual field conditions.
• A direct result is quickly obtained.
Disadvantages:
• The test is more expensive and complicated than the slump test and requires electricity, thus reducing the likelihood it would be used in the field.
• Although the test does measure values related to yield stress and plastic viscosity, the values are not determined in fundamental units.
• The precise end point of the test can be difficult to determine.

The Wigmore consistometer (Scanlon 1994) is a dynamic penetration test that was developed as an improvement of the slump test. The test measures consistency by adding energy to the concrete and measuring penetration resistance.

The apparatus consists of cylindrical container mounted on a drop table. A removable lid placed atop the cylinder includes a hole that guides a graduated rod with an attached 2 inch ball vertically downward through the concrete. To perform the test, concrete is placed into the container and compacted with eight drops of the table. The container is filled to the top and struck off level. The lid with the rod and ball is placed on top of the container. The number of drops required to lower the ball 7 ¾ inches into the concrete is recorded as a measure of consistency.

Typical results vary from 20 drops for soft and fluid concrete to 200 drops for stiff, low slump concrete. Large aggregates can interfere with the descent of the ball and lead to variability in the test results.

Advantages:
• The Wigmore consistometer is a dynamic test that provides a direct result.
• The test can be used on a wide range of concrete workability.
Disadvantages:
• In order to minimize the disproportionate effects of coarse aggregate particles on test
results, the ball should be significantly larger than the maximum coarse aggregate size.
Such a test device would be impractically large.
• Although the results of the test are related both to yield stress and plastic viscosity, results are not expressed in fundamental rheological units.
• The drop table must be mounted on an object of sufficient mass to absorb vibrations created by the drop table. Accordingly, the device is likely to be too large and bulky for field use.

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