Revised air test.

Q. In the past several months, we've been having trouble gaining inspector approval of our concrete when they used the revised air test (ASTM C 173-01). Most testing problems seemed limited to projects where we batched concrete with lightweight aggregate.

The inspectors could not determine

A. According to Gene Daniel, who chairs the ASTM subcommittee responsible for this method, the change in the testing procedure was field driven. The committee received many requests from a wide range of practitioners to help speed the field test by eliminating the waiting period for foam to disperse.

During the discussion stage of the standard review, the committee received a great deal of information of comparative testing of the two procedures. In fact Dick Gaynor, a widely respected researcher in the properties of fresh concrete and the task group leader for handling this test method in ASTM C 09.60, was involved in some of this comparative testing data. Gaynor performed the new procedure with several different air-entraining admixtures and did not encounter the problems in false readings.

So there was minimal concern about field problems when the method was revised. "The verification information available to ASTM C 09.60, at the time C 173 was revised, indicated the revision produced meaningful results in a greatly shortened time period," says Daniel.

That's not to say that the committee and task group members don't recognize that there could be some problems. "After a method is revised we often hear of some problems," says Daniel. "That's why we continue to encourage producers and testing labs to provide the committee with comparative test results."

One problem that the committee heard about was from a producer who has had experience with both methods of air testing. The producer indicated that as long as the plant used an aggregate that doesn't have a high rate of absorption, the revised volumetric air test appeared to work fine.

Initially the producer tried to test concrete batched with No. 67 stone, with a rate of absorption of more than 6% (2.19 ssd). The new procedure caused problems. The producer indicated that the new volumetric air test seemed to pull the air out of the rock and give false air readings. On concrete batched with this material, the old method was the preferred method.

When the producer began to use a coarse aggregate with a much lower absorption of around 2% (2.6 ssd), the volumetric air test was accurate.

Committee members are curious if there's a pattern to the problems with the new method. Are problems more common when the concrete contains lightweight aggregate? Or is the problem focused on mixes with high cement content?

Daniel asks that any specific problems with the test method should be shared with Gaynor at rdgaynor@erols.com or Daniel at dgenedinc@aol.com. The more detail available to the subcommittee and the task group responsible, the quicker the group can determine the best fix for this test.