Mixing and pouring concrete is complex. The material itself is made from components and recipes that vary with temperature, geography and handler. Simple field tests are used on fresh batches of concrete to determine the suitability of the batch for the project at hand. The tests involve a device called an Abrams cone, an inverted mold into which fresh concrete is poured. The inverted cone is held tight to the ground to prevent leakage, and the cone is then lifted off the fresh concrete and the behavior of the liberated concrete is observed.
In the case of a flow test, the Abrams cone is lifted and the concrete forms a puddle with an expanding radius. The diameter of the puddle is measured as soon as it stops expanding and the "flow" informs the workers about the readiness of the concrete for use.
In the case of a slump test, the concrete is firmly tamped down within the Abrams cone before the mold is lifted. This concrete doesn't "flow" as in the flow test; instead it retains much of its shape and height. The amount of height lost as the concrete settles is measured. This value is called the "slump".
The following represents paired tests on 103 samples of concrete.
For slumps of less than 10 cm the highest flow was about
If a 104th sample of concrete produced a 65cm flow and 5 cm of slump and the correlation between flow and slump was then recalculated, the correlation will have