Air entrainment in mass concrete
Tynes, W. O. (William O.); Mather, Bryant.
Technical reportAbstract: In the first phase of this investigation, five low cement content mass concrete mixtures containing crushed limestone aggregate and having nominal air contents up to 12% in the portion of the mixture passing a 1-1/2-in. sieve were made and tested to determine if the 4 to 7% air content range stipulated by current Corps of Engineer practices is optimum. Workability, shrinkage, flexural and compressive strength, and modulus of elasticity tests were made on specimens from three batches of concrete for each mixture. The results of the tests indicated that no basis for determining the optimum air content for mass concrete could be found since no systematic method had been used in proportioning the mixtures of differing air contents. Changes in proportions had been based on the appearance of the mixture and the judgment of the operator. In the second phase of the investigation, fifteen additional mixtures were systematically proportioned; and: tested. In all cases the mixture proportions were adjusted, as the air content was increased, by maintaining the volume of cement and coarse aggregate constant per unit volume of concrete and decreasing the volume of water plus fine aggregate by amounts equal to the volume of air added. The mixtures in this phase were subjected to the same tests as in the first phase except that the tests for shrinkage, flexural strength, modulus of elasticity, and some of the tests for workability were not performed. From previous work it was known that the strength of concrete is reduced 5% for each 1% of air added. This study showed that for each percent of air added if 0.5% of a cubic yard of water is removed from low cement content concrete the effects on concrete strength of adding air and reducing water will be closely balanced. Compressive strength tests tended to confirm this relation when mixtures with water to cement ratios of less than 0.60 were excluded. In the third phase of the investigation, twenty additional mixtures were proportioned and tested. The results of these tests indicated that the water to fine aggregate ratio was not affected by varying the cement content.
Concrete Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Concrete--air entrainment; Mass concrete
Technical report (U.S. Army Engineer Waterways Experiment Station) ; C-69-1.
Approved for public release; distribution is unlimited.