Development and Study of Apparatus and Methods for the Determination of the Air Content of Fresh Concrete


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Title: Development and Study of Apparatus and Methods for the Determination of the Air Content of Fresh Concrete

Author(s): Carl A. Menzel

Publication: Journal Proceedings

Volume: 43

Issue: 5

Appears on pages(s): 1053-1072

Keywords: none

Date: 5/1/1947

Describes new apparatus and methods developed for the determination of the entrained air content of fresh concrete. The test methods developed are based on two different principles, neither of which requires weighing scales: (I Direct Volumetric Method in which the volume o1 air removed from a sample of fresh concrete inundated in an approximately equal volume of water is indicated directly by the volume of liquid required to restore the original liquid level after the removal of the entrained air; (2) Pressure Method (proposed by Klein and Walker) in which the volume of air entrained in a sample of fresh concrete is indicated by the change in volume of the concrete when a known pressure is applied to the sample. Extensive tests show good correlation between the Rolling Method (a direct volumetric method in which air is removed by rolling the concrete in an excess of water) and the Pressure Method for concrete mixes representing a wide range in cement con-tent, consistency, natural coarse aggregate, and method of incorporating the air-entraining agent. Good correlation has also been obtained in tests conducted at four temperatures (44, 62, 79, and 100 F). Both laboratory and field experience with different methods indicate that, all things considered, the pressure method is probably the most practical for field tests. The rolling and modified rolling methods, although equal in dependability to the pressure meth-od, appear to rank second to it in practicability. These studies provided a basis for the design of suitable apparatus for testing 0.22 cu ft concrete samples (with 2-in. maximum size aggregate) by the pressure and rolling methods.