ASTM C231-17 pdf download.Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method.
3. Significance and Use
3.1 This test method covers the determination of the air content of freshly mixed concrete. The test determines the air content offreshly mixed concrete exclusive ofany air that may exist inside voids within aggregate particles. For this reason, it is applicable to concrete made with relatively dense aggregate particles and requires determination ofthe aggregate correction factor (see 6.1 and 9.1).
3.2 This test method and Test Method C138/C138M and C173/C173M provide pressure, gravimetric, and volumetric procedures, respectively, for determining the air content of freshly mixed concrete. The pressure procedure of this test method gives substantially the same air contents as the other two test methods for concretes made with dense aggregates.
3.3 The air content of hardened concrete may be either higher or lower than that determined by this test method. This depends upon the methods and amount of consolidation effort applied to the concrete from which the hardened concrete specimen is taken; uniformity and stability ofthe air bubbles in the fresh and hardened concrete; accuracy of the microscopic examination, if used; time of comparison; environmental exposure; stage in the delivery, placement and consolidation processes at which the air content of the unhardened concrete is determined, that is, before or after the concrete goes through a pump; and other factors. 4. Apparatus 4.1 Air Meters—There are available satisfactory apparatus of two basic operational designs employing the principle of Boyle’s law. For purposes of reference herein these are designated Meter Type A and Meter Type B. 4.1.1 Meter Type A—An air meter consisting ofa measuring bowl and cover assembly (see Fig. 1) conforming to the requirements of 4.2 and 4.3. The operational principle of this meter consists of introducing water to a predetermined height above a sample of concrete of known volume, and the application of a predetermined air pressure over the water. The determination consists of the reduction in volume of the air in the concrete sample by observing the amount the water level is lowered under the applied pressure, the latter amount being calibrated in terms of percent of air in the concrete sample. 4.1.2 Meter Type B—An air meter consisting ofa measuring bowl and cover assembly (see Fig. 2) conforming to the requirements of 4.2 and 4.3. The operational principle of this meter consists of equalizing a known volume of air at a known pressure in a sealed air chamber with the unknown volume of air in the concrete sample, the dial on the pressure gauge being calibrated in terms of percent air for the observed pressure at which equalization takes place. Working pressures of50 to 205 kPa [7.5 to 30.0 psi] have been used satisfactorily. 4.2 Measuring Bowl—The measuring bowl shall be essen- tially cylindrical in shape, made of steel, hard metal, or other hard material not readily attacked by the cement paste, having a minimum diameter equal to 0.75 to 1.25 times the height, and a capacity of at least 6.0 L [0.20 ft 3 ]. It shall be flanged or otherwise constructed to provide for a pressure tight fit between measuring bowl and cover assembly. The interior surfaces of the measuring bowl and surfaces of rims, flanges, and other component fitted parts shall be machined smooth. The measuring bowl and cover assembly shall be sufficiently rigid to limit the expansion factor, D, ofthe apparatus assembly (Section A1.5) to not more than 0.1 % of air content on the indicator scale when under normal operating pressure. 4.3 Cover Assembly: 4.3.1 The cover assembly shall be made ofsteel, hard metal, or other hard material not readily attacked by the cement paste. It shall be flanged or otherwise constructed to provide for a pressure-tight fit between measuring bowl and cover assembly and shall have machined smooth interior surfaces contoured to provide an air space above the level ofthe top ofthe measuring bowl. The cover shall be sufficiently rigid to limit the expan- sion factor of the apparatus assembly as prescribed in 4.2.ASTM C231 pdf download.