Concrete workability is a crucial factor that affects the quality and durability of construction. Among various workability tests, the Powers Remolding Test stands out as a dynamic method developed specifically to assess the plastic shear capacity and workability of concrete, especially low-slump mixes. This article explores the history, procedure, features, advantages, and disadvantages of the Powers Remolding Test.
The Powers Remolding Test is a specialized workability test for concrete that was developed by Powers in 1932. It was later standardized and adopted by the U.S. Army Corps of Engineers under the code CRD C6-74. This test shares some similarities with the vee-bee consistometer test, but with notable differences in its approach to evaluating concrete’s behavior under vibration.
Test Procedure
The test utilizes a 12-inch diameter cylindrical mold mounted on a standard drop table. Attached to the top of the mold is a ring measuring 8 1/4 inches in diameter. A standard slump cone is placed inside this ring, into which the concrete sample is poured and compacted carefully. On top of the concrete, a clear plate with a vertical stem rests, ensuring uniform pressure.
During the test, the drop table is repeatedly dropped, causing the concrete to “remold” or reshape inside the mold. The primary measurement is the number of drops needed for the concrete to change shape and fit the outer cylinder perfectly—this count is known as the “remolding effort.” The ring plays a critical role by restricting lateral movement of the concrete, allowing for the assessment of the concrete mix’s plastic shear capacity.
If the concrete passes through the ring effortlessly with minimal drops, it indicates a high shear capacity and better workability. Conversely, if the concrete struggles to flow through the ring and requires many drops to remold—often clogging inside the ring—it indicates lower shear capacity and reduced workability.
Features of the Powers Remolding Test
One of the key differences between the Powers Remolding Test and the vee-bee test is the mode of vibration: while the vee-bee test uses an electric vibrator, the Powers test relies on physical drops of the table. The test produces a single value—the number of drops required for remolding—which directly reflects the concrete’s workability.
During testing, the drop table generates a high initial shear rate on the concrete, which then quickly drops to zero as the concrete conforms to the mold. This process provides valuable insights into the rheological behavior of concrete, focusing on how the material moves and flows under applied shear stresses.
Advantages of the Powers Remolding Test
The Powers Remolding Test offers several advantages:
- It is a dynamic test, simulating real-world shear stresses more accurately than static tests.
- It is especially suitable for low-slump concrete mixes, which are typically difficult to test using other methods.
- The test delivers direct results without complex calculations or interpretations.
Disadvantages of the Powers Remolding Test
Despite its benefits, the Powers Remolding Test has limitations:
- The drop table must be placed on a surface that can absorb vibrations, which may not always be available on construction sites.
- The equipment setup is bulky and cumbersome, restricting the test’s usability in field conditions.
- The test is only applicable to low-slump concretes, limiting its range of use.
Conclusion
The Powers Remolding Test remains a valuable tool for understanding the workability and shear capacity of low-slump concrete mixes. By focusing on dynamic shear behavior through physical drops, it offers unique insights that help engineers assess concrete performance before application. However, due to equipment size and surface requirements, it is often confined to laboratory environments rather than field use. For those working with low-slump concrete, the Powers Remolding Test provides a reliable and direct measure of mix workability and rheological properties.