1、Designation: C 231 08bStandard 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 r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its
7、 use. It is theresponsibility of the user of this standard to establish appro-priate 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 prolo
8、nged exposure.)22. Referenced Documents2.1 ASTM Standards:3C 138/C 138M Test Method 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
9、192/C 192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryC 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
10、 covers the determination of the aircontent of freshly mixed concrete. The test determines 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 a
11、nd requires determination of the aggregate correctionfactor (see 6.1 and 9.1).3.2 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 t
12、his testmethod gives substantially the same air contents as the othertwo test methods 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 effo
13、rtapplied to the concrete from which the hardened concretespecimen is taken; uniformity 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 consolidationpr
14、ocesses at which the air content of the unhardened concreteis determined, that is, 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 SubcommitteeC
15、09.60 on Testing Fresh Concrete.Current edition approved June 1, 2008. Published July 2008. Originally approvedin 1949. Last previous edition approved in 2008 as C 231 08a.2Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual Book of ASTM Standards, Vol 04.02.3For reference
16、d ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service 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.Copyrigh
17、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, 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 Me
18、ter Type A and Meter Type B.4.1.1 Meter Type AAn air meter consisting of a measuringbowl 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 vol
19、ume, and theapplication of a predetermined air pressure over the water. Thedetermination 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
20、the concrete sample.4.1.2 Meter Type BAn air meter consisting of a measuringbowl and 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 unkno
21、wn volume ofair in the concrete sample, the dial on the pressure gauge beingcalibrated 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 e
22、ssen-tially cylindrical in shape, made of steel, hard metal, or otherhard material 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 pressu
23、re tight fitbetween measuring bowl and cover assembly. The interiorsurfaces 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 sufficientlyrigid to limit the expansion factor, D, of the apparatu
24、s assembly(Annex A1.5) to not more than 0.1 % of air content on theindicator scale when under normal operating 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 cons
25、tructed to provide for apressure-tight fit between measuring bowl and cover assemblyand shall have machined smooth interior surfaces contoured toprovide an air space above the level of the top of the measuringbowl. The cover shall be sufficiently rigid to limit the expan-sion factor of the apparatus
26、 assembly as prescribed in 4.2.4.3.2 The cover assembly shall be fitted with a means ofdirect reading of the air content. 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 gauge attached. In the Type
27、B meter, the dial of thepressure gauge shall be calibrated to indicate the percent of air.Graduations shall be provided 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, airbl
28、eeder valves, and petcocks for bleeding off or through whichwater may be introduced as necessary for the particular meterdesign. Suitable means for clamping the cover to the measuringbowl shall be provided to make a pressure-tight seal withoutentrapping air at the joint between the flanges of the co
29、ver andmeasuring bowl. A suitable hand pump shall be provided withthe cover either as an 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
30、 tested; or, if smaller, 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-tio
31、n, the measure shall be cylindrical in shape and of an insidedepth12 in. (13 mm) less than that of the measuring bowl.NOTE 1Asatisfactory calibration vessel to place within the measuringbowl may be machined from No. 16 gauge brass tubing, of a diameter toprovide the volume desired, to which a brass
32、disk12 in. in thickness issoldered to form an end. When design of the meter requires withdrawingof water from the water-filled measuring bowl and cover assembly, tocheck calibration, the measure may be an integral part of the coverassembly or may be a separate cylindrical measure similar to theabove
33、-described cylinder.4.5 The designs of various 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 satis
34、factorily determine air contentin accordance 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 s
35、hall be so constructed thatwhen water is added 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 ro
36、d58 in. (16 mm) in diameter and not less than16 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 ft
37、3(14 L) or smaller, and a malletweighing approximately 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 Plate
38、A flat rectangular metal plate at least14 in. (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
39、of116 in. (1.5 mm).4.13 Funnel, with the spout fitting into spray tube.C 231 08b24.14 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
40、not less than 2 ft2(0.19m2) of sieving area.4.17 Scoopof a size large enough so each amount ofconcrete obtained from the sampling receptacle is representa-tive and small enough so it is not spilled during placement inthe measuring bowl.5. Calibration of Apparatus5.1 Make calibration tests in accorda
41、nce 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 describedA1.2-A1.6, as applicableto the meter type under consideration, are p
42、rerequisites for thefinal calibration test to determine the operating pressure, P,onthe pressure gauge of the TypeAmeter as described inA1.7,orto determine the accuracy of the graduations indicating aircontent on the dial face of the pressure gauge of the Type Bmeter as described in A1.9. The steps
43、in A1.2-A1.6 need bemade only once (at the time of initial calibration), or onlyoccasionally 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 checked,must be made as frequently as necessary
44、and at intervals not toexceed three months to ensure that the proper gauge pressure,P, is being used for the Type A meter or that the correct aircontents are being indicated on the pressure gauge air contentscale for the Type B meter. A change in elevation of more than600 ft (183 m) from the locatio
45、n at which a Type-A meter waslast calibrated will require recalibration in accordance withA1.7.5.2 Calibration RecordsInformation to be maintained inthe records shall include determination of expansion factor;size of the calibration vessel used; and the reading of the meterat the calibration test po
46、int(s).6. Determination of Aggregate Correction Factor6.1 ProcedureDetermine the aggregate correction factoron a combined sample of fine and coarse aggregate as directedin 6.2 to 6.4. It is determined independently by applying thecalibrated pressure to a sample of inundated fine and coarseaggregate
47、in approximately the same moisture condition,amount, and proportions occurring in the concrete sampleunder test.6.2 Aggregate Sample SizeCalculate the weights of fineand 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!
48、 3 Cb(2)where:Fs= mass of fine aggregate in concrete sample under test,lb (kg),FIG. 1 Illustration of the Pressure Method for Air ContentType-A MeterFIG. 2 Schematic DiagramType-B MeterC 231 08b3S = volume of concrete sample (same as volume ofmeasuring bowl), ft3(m3),B = volume of concrete produced
49、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), andCb= total mass of coarse aggregate in the moisture condi-tion used in batch, lb (kg).NOTE 2The volume 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
