Study of the Effect of Blended Coarse Aggregate on Air Entrained Concrete Second Progress Report

When the first progress report on this study of blended aggregate was prepared in January, 1947, only three of the nine groups of samples in Series I had completed the durability tests, and specimens in four of the seven groups composing Series II had not even been prepared. In contrast, at the present all samples in Series I have completed the durability tests thus concluding the results pertaining to Ohio River gravel from Louisville, and specimens in three groups of Series II (applicable to glacial gravel) have finished the durability tests. Further than that, several additional groups of samples which form a part of the over-all study of combined aggregate materials have been prepared in the interim, and some of these were placed in durability tests several weeks ago. These, however, are of doubtful ultimate value because of defects in operation of equipment, and for that reason--plus the fact that nothing of significance has shown up in the tests--they are not given consideration in this report. As shown in Table I, where the results are summarized, only four sets (or two groups) of specimens were able to withstand freezing and thawing for 200 cycles - the maximum duration of test or point at which beams were removed if failure had not occurred previously. These samples were in Series I, Group G, where the mix contained 100 percent limestone coarse aggregate and 4.3 percent air, and Series II, Group A, which had 100 percent glacial gravel and 6.1 percent air in the mix. Apparently, the unusual durability of the latter must be dependent upon its high air content, because mixes with the same aggregate but only 1.7 percent air (Series C) or even 4.1 nercent air (Series B) could withstand not more than 172 cycles. Thus, for practical purposes all mixes except those with 100 percent limestone and air entrainment failed in less than 200 cycles