Concrete Testing 1

[S2C2]

ASTM C31, Section 7.2 specifically states that concrete used in the air content test shall not be used in fabricating test specimens.

No mention is made concerning the re-use of the concrete that was used in the slump test to fabricate the compression test cylinders.

Comments?

 

[Roadbridge]

When I was a student doing my practical in concrete technology I asked the same question about reusing the sample from the slump test to make cubes. I was told that it was not good practice and not to consider it in the future.

 

[rllipham]

While laboratory tirals for the Florida DOT we are allowed to return the slumps to the mixer. We are using self consolidating concrete (SCC). SCC requires several additional tests beyond slump and air. In order to have enough mix to complete the series we must reurn the slumps to the mixer.

The air content test is a destructive test. By adding the water you change the characteristics of the concrete.

Best practices would be to not reuse the slump concrete. I have used it when the contractor comes to me and asks "Can we get another set of cylinders for an early break?"

 

[Rjeffery]

The intent is to use the same concrete to perform all the tests. By "the same concrete" i mean concrete that has not had additional actions done to it. If you used the roll-r-meter the concrete would have a large amount of water added so of course it would effect the results. the pressure method also adds water so would effect the strength results. when performing the slump test the concrete us additionally manipulated therefore moisture could be lost as well as some of the paste which adhears to the side of the cone, etc.

This being said, the intent of the procedure is to remove as much error as possable between operators. reusing any portion of the test sample introduces error that can't be quantified and therefore can't be removed.