The following letter was received concerning the article titled “Measurement of Air Content in Concrete,” which was published in HPC Bridge Views, Issue No. 61, May/June 2010.
Editor
The article describes various methods for measuring the air content of concrete. I think we do a disservice when including the Chace Air Indicator in any discussion of test methods. The very title of the apparatus, “Air Indicator,” removes it from the category of test methods. The small sample is a concern. If there is a suspicion that the air content is out of specification, a more accurate method would need to be used prior to acceptance/rejection. I have had experience with concrete being rejected on the basis of results from the Chace Air Indicator and it is very difficult to absorb the financial loss when the concrete may well be within specification.
I would encourage the mandatory use of the gravimetric method in conjunction with the pressure or volumetric methods especially on critical placements. There have been enough instances of false readings in high performance concretes (especially on the high end) that would have been caught by gravimetric testing prior to placement. The mechanics are simple and the results are valuable. And gravity seems to be fairly consistent.
Thomas H. Adams, Executive Director
American Coal Ash Association
Editor’s Response
The Chace Air Indicator is an AASHTO standard method of test. Rather than ignore it, we included it but then pointed out its limitations and that it should not be used for determining compliance with the specifications.