In our report entitled "A Summary of Experiments With Air Entrainment in Cement Concrete" released last September, we recommended among other things that "The gravimetric method (A.S.T.M. Designation: C138-44) be used only as a temperary expedient for determining air contents until the pressure method or some method not dependent upon physical properties of aggregates and not influenced by other variables can be firmly established" (see item 3, page 66 of that report). At that time we were thinking of the pressure apparatus demonstrated by representatives of the Portland Cement Association during construction of the Lexington-Nicholasville Road (Project F 524 (1)-1; S.P. 34-124). Results from the few pressure tests made on that job and listed in Table VI of our report were in such close accord with those determined simultaneously by the gravimetric method, that we purchased an air meter for the purpose of conducting more comparative tests in the laboratory.

Results of seventeen comparative tests on mixes with different aggregates, cements, cement factors, and designed air contents are summarized in Table I attached to this memorandum. Also attached are some suggested changes in our 1945 Standard Specifications; changes which are in line with the recommendations which we made last September and which we are prepared to supplement on the basis of these tests with the air meter. One proposed addition to the Specifications, dealing with HP-7 as an admixture, has not been formulated because we did not have sufficient time to establish specific requirements on a product not included heretofore in other specifications. In our suggested version of Article 4.1.8 we made reference to an Article 7.42.3 intended to cover the HP-7, and information for such an article could be worked up possibly within a week's time if the Research Board so desires. Also, nothing has been suggested for the text of a Supplement to the Field Testing Nanual which is referred to in every article. This supplement or an equivalent would be necessary in order to define the equipment and procedure for the test.

Report Date


Report Number

No. 21

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