Title:
Alternative Means of Measuring Air Content in Fresh Concrete
Author(s):
K. H. Khayat, K. W. Nasser, and W. Hester
Publication:
Materials Journal
Volume:
87
Issue:
4
Appears on pages(s):
355-362
Keywords:
air-entraining agents; air entrainment; fresh concretes; air meters; measuring instruments; plasticizers; Materials Research
DOI:
10.14359/2076
Date:
7/1/1990
Abstract:
The correlations of a new air meter, mini air meter, and two other ASTM standard air meters were examined to establish the reliability of the new apparatus. The mini air meter uses the volumetric principle to determine the air content of fresh concrete. It weighs 8 lb (3.63 kg) and requires a concrete sample that is approximately one-eleventh and one-twenty eighth the size of that needed by the conventional roller and pressure meters, respectively. The laboratory work involved testing the air content of 21 fresh concrete mixtures using the mini, roller, and pressure air meters. Both 3/8 and 1 in. (9.5 and 25.4 mm) nominal-size aggregates were used for making normal weight and lightweight concretes. The water-to-cementitious materials ratios of the mixes ranged between 0.22 and 0.51. The cement content varied from 450 to 910 lb/yd3 (267 to 540 kg/m3), with silica fume added to some mixes. All mixes incorporated superplasticizers. Air-entraining agents were also added to yield air content between 1.25 and 12.5 percent. Results indicate that the mini air meter exhibits excellent linear correlations with the other standard tests and can provide a quick means for monitoring the air content. For the materials employed in this investigation, the accuracy of air volume measurements recorded with the mini air meter does not seem to be influenced by the density of the aggregate, nominal size of the aggregate, cement content, water-to-cementitious materials ratio, or the presence of additives.