The K Slump test is covered by ASTM C 1362.
This device is used to determine the workability and degree of compaction of fresh concrete after being placed in the forms. It can be used for in-situ measurements or inside test moulds and forms. Results can theoretically be correlated against the slump test.
The test is very simple: insert the tester into the concrete up to the level of the disc, after 60 seconds, a measuring rod is lowered onto the surface of the concrete and the K-slump is read directly on a scale.