Researchers perform a penetration test with an inverted slump cone.
The SCC mixture in this penetration test is classified as “unstable.”
The device is designed so that the drop of the penetration head represents movement of coarse aggregates in the fresh SCC. The mass of the penetration head was important to the test's effectiveness. The proposed standard calls for the penetration head to be 45 g.
The penetration device is simple and inexpensive to construct. It's also sturdy enough to survive in both the field and lab.How the test is conducted
Technicians first identify a test area that's level and free from vibration. They next place the dampened slump cone with the smaller opening facing down. After gathering a sample of concrete representative of the batch obtained according to the procedures in ASTM C 172, the technician immediately fills the slump cone in one lift and avoids placing all of the sample in one location.
There should be enough test material to slightly overfill the slump cone's top. The technician concludes this preparation by leveling the upper surface with a strike-off bar.
The technician then places the penetration apparatus on the slump cone's top. The penetration cylinder is aligned to the cone's center. Before the test, the apparatus supports the penetration so it is just above the fresh concrete's surface.
After about two minutes, the technician releases a locking screw that allows the penetration cylinder to gently lower and come to rest on the concrete's surface. The cylinder will slowly drop into the fresh concrete from its own weight.
The procedure requires the technician to observe this dropping action for 30 seconds. The technician then records the penetration depth.
After the reading, the penetration apparatus is removed from the slump cone's rim. Since the SCC is still fresh, the technician can raise the cone to conduct a slump flow test.A real number
The BASF researchers used this procedure to test 34 SCC mixes that each had different levels of static stability, as determined by VSI observations. The team also tested each mix with the slump flow test and the column segregation test. In its report, the team provided information containing mix ingredients and proportions.
By comparing the rapid penetration results to those of the VSI and column segregation tests, the BASF team found a very strong correlation. It was able to offer a quantitative-based stability classification. The researchers found:Highly stable SCC mixes – Penetration depths less than or equal to 10 mm;Stable SCC mixes – Penetration depths greater than 10 mm but less than or equal to 25 mm;Unstable SCC mixes – Penetration depths greater than 25 mm.
Reference: “A Rapid Test for Segregation Resistance of Self-Consolidating Concrete,” by Van Bui, Emmanuel Attiogbe, Dan Vojtko, Steve Schaef, and Heather See, 2007 Concrete Technology Forum, National Ready Mixed Concrete Association.
For more information on this test, e-mail Van Bui firstname.lastname@example.org Emmanuel Attiogbe email@example.com.Or telephone BASF Construction Chemicals, Admixture Systems, in Cleveland at 216-839-7362.