1、Designation: C 231 04Standard Test Method forAir Content of Freshly Mixed Concrete by the PressureMethod1This standard is issued under the fixed designation C 231; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers determination of t
3、he air contentof freshly mixed concrete from observation of the change involume of concrete with a change in pressure.1.2 This test method is intended for use with concretes andmortars made with relatively dense aggregates for which theaggregate correction factor can be satisfactorily determined byt
4、he technique described in Section 6. It is not applicable toconcretes made with lightweight aggregates, air-cooled blast-furnace slag, or aggregates of high porosity. In these cases, TestMethod C 173/C 173M should be used. This test method isalso not applicable to nonplastic concrete such as is comm
5、onlyused in the manufacture of pipe and concrete masonry units.1.3 The text of this test method references notes andfootnotes that provide explanatory information. These notesand footnotes (excluding those in tables and figures) shall notbe considered as requirements of this standard.1.4 The values
6、stated in inch-pound units are to be regardedas the standard. The values given in parentheses are forinformation only.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-pria
7、te safety and health practices and determine the applica-bility of regulatory limitations prior to use. (WarningFreshhydraulic cementitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.)22. Referenced Documents2.1 ASTM Standards:3C 138/C 138M Test Metho
8、d for Density (Unit Weight),Yield, and Air Content (Gravimetric) of ConcreteC 172 Practice for Sampling Freshly Mixed ConcreteC 173/C 173M Test Method for Air Content of FreshlyMixed Concrete by the Volumetric MethodC 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the Laboratory
9、C 670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsE 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3. Significance and Use3.1 This test method covers the determination of the aircontent of freshly mixed concrete. The test de
10、termines the aircontent of freshly mixed concrete exclusive of any air that mayexist inside voids within aggregate particles. For this reason, itis applicable to concrete made with relatively dense aggregateparticles and requires determination of the aggregate correctionfactor (see 6.1 and 9.1).3.2
11、This test method and Test Method C 138/C 138M andC 173/C 173M provide pressure, gravimetric, and volumetricprocedures, respectively, for determining the air content offreshly mixed concrete. The pressure procedure of this testmethod gives substantially the same air contents as the othertwo test meth
12、ods for concretes made with dense aggregates.3.3 The air content of hardened concrete may be eitherhigher or lower than that determined by this test method. Thisdepends upon the methods and amount of consolidation effortapplied to the concrete from which the hardened concretespecimen is taken; unifo
13、rmity and stability of the air bubbles inthe fresh and hardened concrete; accuracy of the microscopicexamination, if used; time of comparison; environmentalexposure; stage in the delivery, placement and consolidationprocesses at which the air content of the unhardened concreteis determined, that is,
14、 before or after the concrete goes througha pump; and other factors.1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates, and is the direct responsibility of SubcommitteeC09.60 on Testing Fresh Concrete.Current edition approved July 1, 2004. Published
15、July 2004. Originally approvedin 1949. Last previous edition approved in 2003 as C 231 03.2Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual Book of ASTM Standards, Vol 04.02.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Se
16、rvice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
17、428-2959, United States.4. Apparatus4.1 Air MetersThere are available satisfactory apparatusof two basic operational designs employing the principle ofBoyles law. For purposes of reference herein these aredesignated Meter Type A and Meter Type B.4.1.1 Meter Type AAn air meter consisting of a measuri
18、ngbowl and cover assembly (see Fig. 1) conforming to therequirements of 4.2 and 4.3. The operational principle of thismeter consists of introducing water to a predetermined heightabove a sample of concrete of known volume, and theapplication of a predetermined air pressure over the water. Thedetermi
19、nation consists of the reduction in volume of the air inthe concrete sample by observing the amount the water level islowered under the applied pressure, the latter amount beingcalibrated in terms of percent of air in the concrete sample.4.1.2 Meter Type BAn air meter consisting of a measuringbowl a
20、nd cover assembly (see Fig. 2) conforming to therequirements of 4.2 and 4.3. The operational principle of thismeter consists of equalizing a known volume of air at a knownpressure in a sealed air chamber with the unknown volume ofair in the concrete sample, the dial on the pressure gage beingcalibra
21、ted in terms of percent air for the observed pressure atwhich equalization takes place. Working pressures of 7.5 to30.0 psi (51 to 207 kPa) have been used satisfactorily.4.2 Measuring BowlThe measuring bowl shall be essen-tially cylindrical in shape, made of steel, hard metal, or otherhard material
22、not readily attacked by the cement paste, havinga minimum diameter equal to 0.75 to 1.25 times the height, anda capacity of at least 0.20 ft3(5.7 L). It shall be flanged orotherwise constructed to provide for a pressure tight fitbetween bowl and cover assembly. The interior surfaces of thebowl and s
23、urfaces of rims, flanges, and other component fittedparts shall be machined smooth. The measuring bowl andcover assembly shall be sufficiently rigid to limit the expansionfactor, D, of the apparatus assembly (Annex A1.5) to not morethan 0.1 % of air content on the indicator scale when undernormal op
24、erating pressure.4.3 Cover Assembly:4.3.1 The cover assembly shall be made of steel, hard metal,or other hard material not readily attacked by the cement paste.It shall be flanged or otherwise constructed to provide for apressure-tight fit between bowl and cover assembly and shallhave machined smoot
25、h interior surfaces contoured to providean air space above the level of the top of the measuring bowl.The cover shall be sufficiently rigid to limit the expansionfactor of the apparatus assembly as prescribed in 4.2.4.3.2 The cover assembly shall be fitted with a means ofdirect reading of the air co
26、ntent. The cover for the Type Ameter shall be fitted with a standpipe, made of a transparentgraduated tube or a metal tube of uniform bore with a glasswater gage attached. In the Type B meter, the dial of thepressure gage shall be calibrated to indicate the percent of air.Graduations shall be provid
27、ed for a range in air content of atleast 8 % readable to 0.1 % as determined by the proper airpressure calibration test.4.3.3 The cover assembly shall be fitted with air valves, airbleeder valves, and petcocks for bleeding off or through whichFIG. 1 Illustration of the Pressure Method for Air Conten
28、tType-A MeterFIG. 2 Schematic DiagramType-B MeterC231042water may be introduced as necessary for the particular meterdesign. Suitable means for clamping the cover to the bowl shallbe provided to make a pressure-tight seal without entrappingair at the joint between the flanges of the cover and bowl.
29、Asuitable hand pump shall be provided with the cover either asan attachment or as an accessory.4.4 Calibration VesselA measure having an internal vol-ume equal to a percent of the volume of the measuring bowlcorresponding to the approximate percent of air in the concreteto be tested; or, if smaller,
30、 it shall be possible to checkcalibration of the meter indicator at the approximate percent ofair in the concrete to be tested by repeated filling of themeasure. When the design of the meter requires placing thecalibration vessel within the measuring bowl to check calibra-tion, the measure shall be
31、cylindrical in shape and of an insidedepth12 in. (13 mm) less than that of the bowl.NOTE 1A satisfactory calibration vessel to place within the measuringbowl may be machined from No. 16 gage brass tubing, of a diameter toprovide the volume desired, to which a brass disk12 in. in thickness issoldered
32、 to form an end. When design of the meter requires withdrawingof water from the water-filled bowl and cover assembly, to checkcalibration, the measure may be an integral part of the cover assembly ormay be a separate cylindrical measure similar to the above-describedcylinder.4.5 The designs of vario
33、us available types of air meters aresuch that they differ in operating techniques; therefore, all ofthe items described in 4.6-4.16 may not be required. The itemsrequired shall be those necessary for use with the particulardesign of apparatus used to satisfactorily determine air contentin accordance
34、 with the procedures prescribed herein.4.6 Coil Spring or Other Device for Holding CalibrationCylinder in Place.4.7 Spray TubeA brass tube of appropriate diameter,which may be an integral part of the cover assembly, or whichmay be provided separately. It shall be so constructed thatwhen water is add
35、ed to the container, it is sprayed to the wallsof the cover in such a manner as to flow down the sides causinga minimum of disturbance to the concrete.4.8 TrowelA standard brick masons trowel.4.9 Tamping RodThe tamping rod shall be a roundstraight steel rod58 in. (16 mm) in diameter and not less tha
36、n16 in. (400 mm) in length, having the tamping end rounded toa hemispherical tip the diameter of which is58 in. (16 mm).4.10 MalletA mallet (with a rubber or rawhide head)weighing approximately 1.25 6 0.50 lb (0.57 6 0.23 kg) foruse with measures of 0.5 ft3(14 L) or smaller, and a malletweighing app
37、roximately 2.25 6 0.50 lb (1.02 6 0.23 kg) foruse with measures larger than 0.5 ft3(14 L).4.11 Strike-Off BarA flat straight bar of steel or othersuitable metal at least18 in. (3 mm) thick and34 in. (20 mm)wide by 12 in. (300 mm) long.4.12 Strike-Off PlateA flat rectangular metal plate at least14 in
38、. (6 mm) thick or a glass or acrylic plate at least12 in. (12mm) thick with a length and width at least 2 in. (50 mm)greater than the diameter of the measure with which it is to beused. The edges of the plate shall be straight and smooth withina tolerance of116 in. (1.5 mm).4.13 Funnel, with the spo
39、ut fitting into spray tube.4.14 Measure for Water, having the necessary capacity tofill the indicator with water from the top of the concrete to thezero mark.4.15 Vibrator, as described in Practice C 192/C 192M.4.16 Sieves,112-in. (37.5-mm) with not less than 2 ft2(0.19m2) of sieving area.5. Calibra
40、tion of Apparatus5.1 Make calibration tests in accordance with proceduresprescribed in the annex. Rough handling will affect thecalibration of both Types A and B meters. Changes in baro-metric pressure will affect the calibration of Type A meter butnot Type B meter. The steps described A1.2 to A1.6,
41、 asapplicable to the meter type under consideration, are prerequi-sites for the final calibration test to determine the operatingpressure, P, on the pressure gage of the Type A meter asdescribed in A1.7, or to determine the accuracy of thegraduations indicating air content on the dial face of thepre
42、ssure gage of the Type B meter. The steps in A1.2 to A1.6need be made only once (at the time of initial calibration), oronly occasionally to check volume constancy of the calibrationcylinder and measuring bowl. The calibration test described inA1.7 and A1.9, as applicable to the meter type being che
43、cked,must be made as frequently as necessary and at intervals not toexceed three months to ensure that the proper gage pressure, P,is being used for the Type A meter or that the correct aircontents are being indicated on the pressure gage air contentscale for the Type B meter. A change in elevation
44、of more than600 ft (183 m) from the location at which a Type-A meter waslast calibrated will require recalibration in accordance withA1.7.6. Determination of Aggregate Correction Factor6.1 ProcedureDetermine the aggregate correction factoron a combined sample of fine and coarse aggregate as directed
45、in 6.2 to 6.4. It is determined independently by applying thecalibrated pressure to a sample of inundated fine and coarseaggregate in approximately the same moisture condition,amount, and proportions occurring in the concrete sampleunder test.6.2 Aggregate Sample SizeCalculate the weights of fineand
46、 coarse aggregate present in the sample of fresh concretewhose air content is to be determined, as follows:Fs5 S/B! 3 Fb(1)Cs5 S/B! 3 Cb(2)where:Fs= mass of fine aggregate in concrete sample under test,lb (kg),S = volume of concrete sample (same as volume ofmeasuring bowl), ft3(m3),B = volume of con
47、crete produced per batch (Note 2), ft3(m3),Fb= total mass of fine aggregate in the moisture conditionused in batch, lb (kg),Cs= mass of coarse aggregate in concrete sample undertest, lb (kg), andC231043Cb= total mass of coarse aggregate in the moisture condi-tion used in batch, lb (kg).NOTE 2The vol
48、ume of concrete produced per batch can be deter-mined in accordance with applicable provisions of Test Method C 138/C 138M.NOTE 3The term “weight” is temporarily used in this test methodbecause of established trade usage. The word is used to mean both “force”and “mass,” and care must be taken to det
49、ermine which is meant in eachcase (SI unit for force = newton and for mass = kilogram).6.3 Placement of Aggregate in Measuring BowlMix rep-resentative samples of fine aggregate Fsand coarse aggregateCs, and place in the measuring bowl filled one-third full withwater. Place the mixed aggregate, a small amount at a time,into the measuring bowl; if necessary, add additional water soas to inundate all of the aggregate. Add each scoopful in amanner that will entrap as little air as possible and removeaccumulations of foam promptly. Tap the sides of the bo
