Q: We are thinking about proposing the use of self-consolidating concrete on an upcoming project, but one challenge we face is coming up with acceptance criteria everybody feels comfortable with. What’s going on with the development of standardized tests for SCC?
A: Several test methods have become popular for attributes such as slump flow and the ability to pass through congested rebar. Those who are using SCC have generally agreed on the best methods for running the tests and interpreting the results, but all the paperwork hasn’t been filed yet, so there are currently no ASTM standards to reference. However, progress is being made, and at least two test methods should gain approval very soon.
ASTM's subcommittee on self-consolidating concrete met December 6 in Washington to address the few remaining issues related to standard specifications for the static segregation test, which measures stability (ability to resist segregation), and the slump flow test, which measures flow. Following recent votes on both documents, the one remaining question focused on how to incorporate a discussion of segregation in these relatively fluid concrete mixes. It seems likely that with the revisions the committee adopted, these standards will pass on the next ballot and the published documents should then become available sometime next year.
You should be aware that a large part of resolving the segregation issue was understanding that different applications require different mix designs. Even with standardized test methods, it is still necessary to confirm that a mix design is suitable for its intended purpose—especially with SCC. For example, while these test methods will describe in detail how to measure slump flow and segregation, they don’t state an acceptable range for these values, but rather defer to the project specifications.
Round-robin testing has been completed on a third test, the J-ring test, which measures passability (ability to flow through congested rebar). That document is nearing completion and should be put up for a vote soon.
A fourth test, the U-box test, which measures fillability, is growing in use in this country. The subcommittee voted to initiate development of a standard test procedure for that test as well. If you have an interest in contributing to that effort, visit the C09.47 section of the ASTM Web site, www.astm.org.