The study reported here has revealed very poor agreement between air contents determined by the Chace air indicator (CAI) and those by the pressure method. In tests of highway concretes the pressure method gave values typically 30% higher than anticipated based on the CAI readings, which could result in the production of concrete with lower than anticipated strengths. The poor agreement was found to involve relationships between the volumes of the stems, the volume of the bowls, and the mortar correction factors supplied by the manufacturers of the CAI. Consequently, it is recommended that AASHTO Specification T199-72 be modified to account for these relationships. It is concluded that the CAI can be used to provide a reasonably accurate indication of the air content of fresh concrete, when the results are based on the average of tests on a minimum of two samples and the results are corrected using a Chace conversion nomograph that takes into account the Chace factor (the volume of one graduation on the stem as a percentage of the volume of the bowl), the mortar content of the concrete, and the tendency of the CAI to provide a low result at high air contents.
This report contains the reprint of six articles on the subject of quality assurance that have appeared in the past issues of "Public Roads" magazine....
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