Observations at the Research Council, coupled with the national interest in possible changes in the air void characteristics of air-entrained concretes because of the wide use of admixtures and changes in cement properties, raised a question as to whether or not there was a progressive increase over the years in the size of air voids being incorporated in concrete. Thus, the main objective of the study reported here was to evaluate the changes in air void characteristics of hardened concrete as determined by ASTM C457 and by other means for concrete produced in Virginia from 1945 to 1980. Air void parameters including the air content, specific surface, and spacing factor --were determined on 630 concretes. The results did not indicate an overall significant increase in the size of air voids; however, it was observed that, in general, they did show that the average size and the distribution of the voids were marginal compared to generally accepted values. While this finding indicates that air voids may not be as small as optimum, the freeze-thaw performance of air-entrained concretes in Virginia supplied under the present specifications generally has been satisfactory.
The properties of hydraulic cement concretes containing silica fume were investigated to assess their suitability for use in overlays with s minimum t...
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