Two tests for fresh self-consolidating concrete (SCC) are now available as ASTM standard test methods, but only the slump flow test serves much use in the field. But a test being developed at the University of Illinois also looks promising for field use.

At the ASTM sub-committee on self-consolidating concrete's meeting in Toronto in June, Leslie J. Struble, a professor at the University of Illinois, presented an overview of a new Segregation Probe that may provide a rapid and reliable field indication of SCC mix stability.

The probe is similar to a spindle for holding papers. It weighs 18 grams and consists of a 2.38 mm (3/32-inch) diameter steel wire bent into a 100 mm circle and a 150 mm rod, which is at right angles to the plane of the circle. After penetrating the cement paste at the top of the cylinder, the device settles atop the aggregates it encounters below the surface.

To run the test, the probe is placed on the top surface of a concrete cylinder two minutes after it has been cast. After allowing it to settle for one minute, its penetration depth is read. A stability rating is assigned based on that reading. If it settles less than 4 mm, it is rated 0. Settlement of 4-7 mm is rated 1, from 7-25 mm is rated 2, and greater than 25 mm is rated 3. Ratings of 0 and 1 are stable; 2 and 3 are unstable.

Correlation has been very good between measurements using the segregation probe, which can be in a very few minutes, and results of the column segregation test, which take 30 minutes. Because even small changes in aggregate moisture content or admixture dosages can significantly affect the stability of SCC, the segregation probe may be useful in the field.