AASHTO TP 118:17(2018) Standard Method of Test for Characterization of the Air-Void System of Freshly Mixed Concrete by the Sequential Pressure Method.
3.1. This test method covers the determination of the air content and the system air metric (SAM) number of freshly mixed concrete. The test determines the air content of freshly mixed concrete exclusive of any air that exists inside voids within aggregate particles. For this reason, it is applicable only to concrete made for which the aggregate correction factor can be determined. (See Sections 7.1 and 10.1.)
3.2. This test method and T 152, T l2lM/T 121, and T 196M/T 196 provide sequential pressure, static pressure, gravirnetric, and volumetric procedures, respectively, for determining the air content of freshly mixed concrete. The sequential pressure procedure of this test method gives substantially the same air content as the other test methods for concrete made with dense aggregates. The sequential pressure procedure of this test method also gives the SAM number, which can be used to estimate the freeze-thaw durability of the paste in a hardened concrete mixture.
3.3. The air content of the same hardened concrete mixture may be either higher or lower than determined by this test method. This depends on the methods and amount of consolidation effort applied to the concrete from which the hardened concrete specimen is taken; uniformity and stability of the air voids in the fresh and hardened concrete; accuracy of the microscopic examination to measure the hardened air content, if used: time of comparison; environmental exposure; stage in the delivery, placement, and consolidation processes at which the air content is determined, that is, before or after the concrete goes through a pump: and other factors.
3.4. In cases where the air content did not vary between the fresh and hardened concrete, this test method has shown to predict freeze-thaw durability as well as the spacing factor as measured by ASTM C457/C457M.
4.1 Air Meter—A device consisting of a measuring bowl and cover assembly as shown in Figure 1 conforming to the requirements of Sections 4.2 and 4.3. The operational principle of this meter consists of sequentially equalizing known volumes of air in a sealed air chamber, at a series of known pressures, with the unknown volume of air in the concrete sample placed in the measuring bowl. A digital pressure gauge with 0.01 psi (0.07 kPa) accuracy shall be used. The digital gauge shall be able to compute and report the air content within 0.1 percent and the SAM number to 0.01 psi (0.07 kPa). The cover assembly shall be fixed to the measuring bowl with the same uniform pressure that was used during the calibration of the meter.AASHTO TP 118 pdf download.