The “Lump” Test

The slump test, a standard test for concrete, has been adopted as a common test for paste and thickened tailings. While the slump test is nominally quantita- tive (i.e., it gives a value for slump in millimetres), it measures a vaguely defined qualitative parameter (“workability”). To make the test more useful for design purposes, it is desirable to relate slump to measurable physical parameters, par- ticularly the slurry density and the apparent yield stress. For laboratory work, the cylinder slump test has been found to be more practical than the cone slump test, mainly due to the smaller test sample size. The Cylinder Model often used to correlate cylinder slump and yield stress has been shown to be consistent with vane test results for moderate to high relative slumps. However, at lower relative slumps the Cylinder Model consistently underestimates the yield stress. This pa- per discusses a variety of concepts relating to the rheological interpretation of the slump test. It also presents a semi-empirical model (the “Lump Model”) that extends the correlation range of the Cylinder Model and is simpler and easier to use. 74 Paste 2005, Santiago, Chile The “Lump” Test Hallbom, D.J.