Tests of Concrete Containing Air-Entraining Portland Cements or Air-Entraining Materials Added to Batch at Mixer
H. F. Gonnerman
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Presents some of the more significant results obtained in extensive laboratory studies made in connection with the construction of 18 experimental road projects, and in several separate laboratory investigations conducted during the past 6 years with air-entraining portland cements, and with air-entraining materials added at the mixer. Concrete specimens from nearly every experimental road project and from all laboratory series were subjected to scaling and to freezing and thawing tests. These specimens consisted of slabs made in the field from the concrete used in the pavement, of cores drilled from the pavement, and of many prisms made in the laboratory from the cements used in the roads. The laboratory studies included also many slabs and prisms made with various cements. Resistance to scaling, and to freezing and thaw-ing while immersed, was markedly improved when the concrete was made with air-entraining portland cements, or with air-entraining materials added at the mixer. Increase in air content of the concrete caused reductions in flexural and compressive strength. Suppl. 1944. See also 40-26, 4 l-5, 42-4, 42-15, and 42-24 to 42-38. both strength- and resistance to freezing and thaw- Each percentage point increase in air content reduced excellent performance was obtained when the total amount of entrained air in the fresh concrete was about 3 percent, or about 2 percentage points the modulus of rupture 2 to 3 percent and the com-pressive strenqth 3 to 5 percent. Taking into account higher than that of concrete without air-entraining additions. With this percentage of air, the loss in strength was generally not more than 6 percent in flexure and IO percent in compression. Higher air contents than 3 percent caused greater reductions in strength without any compensating increase in resistance to scaling and to freezing and thawing. The performance under service conditions of ex-perimental paving projects constructed since 1938 with air-entraining portland cements parallels the results of the laboratory studies. Supplementary data - H. F. Gonnerman - Nov.