1、Designation: C 138/C 138M 08American Association StateHighway and Transportation Officials StandardAASHTO No.: T121Standard Test Method forDensity (Unit Weight), Yield, and Air Content (Gravimetric)of Concrete1This standard is issued under the fixed designation C 138/C 138M; the number immediately f
2、ollowing the designation indicates the yearof original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been a
3、pproved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers determination of the density(see Note 1) of freshly mixed concrete and gives formulas forcalculating the yield, cement content, and air content of theconcrete. Yield is defined as the volume of concrete pro
4、ducedfrom a mixture of known quantities of the component materi-als.1.2 The values stated in either inch-pound or SI units shallbe regarded separately as standard. The SI units are shown inbrackets. The values stated might not be exact equivalents;therefore each system must be used independently of
5、the other.NOTE 1Unit weight was the previous terminology used to describethe property determined by this test method, which is mass per unitvolume.1.3 The text of this test method references notes andfootnotes that provide explanatory information. These notesand footnotes (excluding those in tables)
6、 shall not be consid-ered as requirements of this test method.2. Referenced Documents2.1 ASTM Standards:2C 29/C 29M Test Method for Bulk Density (“Unit Weight”)and Voids in AggregateC 150 Specification for Portland CementC 172 Practice for Sampling Freshly Mixed ConcreteC 188 Test Method for Density
7、 of Hydraulic CementC 231 Test Method for Air Content of Freshly MixedConcrete by the Pressure Method3. Terminology3.1 Symbols:A = air content (percentage of voids) in the concreteC = actual cement content, lb/yd3or kg/m3Cb= mass of cement in the batch, lb or kgD = density (unit weight) of concrete,
8、 lb/ft3or kg/m3M = total mass of all materials batched, lb or kg (see Note3)Mc= mass of the measure filled with concrete, lb or kgMm= mass of the measure, lb or kgRy= relative yieldT = theoretical density of the concrete computed on anairfree basis, lb/ft3or kg/m3(see Note 2)Y = yield, volume of con
9、crete produced per batch, yd3orm3Yd= volume of concrete which the batch was designed toproduce, yd3or m3Yf= volume of concrete produced per batch, ft3V = total absolute volume of the component ingredientsin the batch, ft3or m3Vm= volume of the measure, ft3or m3NOTE 2The theoretical density is, custo
10、marily, a laboratory determi-nation, the value for which is assumed to remain constant for all batchesmade using identical component ingredients and proportions. It is calcu-lated from the following equation:T 5 M/V (1)The absolute volume of each ingredient in cubic feet is equal to thequotient of t
11、he mass of that ingredient divided by the product of itsspecific gravity times 62.4. The absolute volume of each ingredient incubic metres is equal to the mass of the ingredient in kilograms divided by1000 times its specific gravity. For the aggregate components, the bulkspecific gravity and mass sh
12、ould be based on the saturated, surface-drycondition. For cement, the actual specific gravity should be determined byTest Method C 188. A value of 3.15 may be used for cements manufac-tured to meet the requirements of Specification C 150.NOTE 3The total mass of all materials batched is the sum of th
13、emasses of the cement, the fine aggregate in the condition used, the coarseaggregate in the condition used, the mixing water added to the batch, andany other solid or liquid materials used.1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the
14、 direct responsibility of SubcommitteeC09.60 on Testing Fresh Concrete.Current edition approved March 1, 2008. Published March 2008. Originallyapproved in 1938. Last previous edition approved in 2007 as C 138/C 138M 07.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
15、STM 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Cons
16、hohocken, PA 19428-2959, United States.4. Apparatus4.1 BalanceA balance or scale accurate to 0.1 lb 45 g orto within 0.3 % of the test load, whichever is greater, at anypoint within the range of use. The range of use shall beconsidered to extend from the mass of the measure empty tothe mass of the m
17、easure plus its contents at 160 lb/ft32600kg/m3.4.2 Tamping RodA round, straight steel rod,58 in. 16mm in diameter and approximately 24 in. 600 mm in length,having the tamping end rounded to a hemispherical tip thediameter of which is58 in.4.3 Internal VibratorInternal vibrators may have rigid orfle
18、xible shafts, preferably powered by electric motors. Thefrequency of vibration shall be 7000 vibrations per minute orgreater while in use. The outside diameter or the side dimen-sion of the vibrating element shall be at least 0.75 in. 19 mmand not greater than 1.50 in. 38 mm. The length of the shaft
19、shall be at least 24 in. 600 mm.4.4 MeasureAcylindrical container made of steel or othersuitable metal (see Note 4). The minimum capacity of themeasure shall conform to the requirements of Table 1 based onthe nominal size of aggregate in the concrete to be tested. Allmeasures, except for measuring b
20、owls of air meters which arealso used for Test Method C 138/C 138M tests, shall conformto the requirements of Test Method C 29/C 29M. When mea-suring bowls of air meters are used, they shall conform to therequirements of Test Method C 231, and shall be calibrated forvolume as described in Test Metho
21、d C 29/C 29M. The top rimof the air meter bowls shall be smooth and plane within 0.01 in.0.3 mm (see Note 5).NOTE 4The metal should not be readily subject to attack by cementpaste. However, reactive materials such as aluminum alloys may be usedin instances where as a consequence of an initial reacti
22、on, a surface filmis rapidly formed which protects the metal against further corrosion.NOTE 5The top rim is satisfactorily plane if a 0.01-in. 0.3-mm feelergage cannot be inserted between the rim and a piece of14-in. 6-mm orthicker plate glass laid over the top of the measure.4.5 Strike-Off PlateA f
23、lat 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 mmgreater 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.
24、 2 mm.4.6 MalletA mallet (with a rubber or rawhide head)having a mass of 1.25 6 0.50 lb 600 6 200 g for use withmeasures of 0.5 ft314 L or smaller, and a mallet having amass of 2.25 6 0.50 lb 1000 6 200 g for use with measureslarger than 0.5 ft3.4.7 Scoopof a size large enough so each amount ofconcr
25、ete obtained from the sampling receptacle is representa-tive and small enough so it is not spilled during placement inthe measure.5. Sample5.1 Obtain the sample of freshly mixed concrete in accor-dance with Practice C 172.6. Procedure6.1 Base the selection of the method of consolidation on theslump,
26、 unless the method is stated in the specifications underwhich the work is being performed. The methods of consoli-dation are rodding and internal vibration. Rod concretes with aslump greater than 3 in. 75 mm. Rod or vibrate concrete witha slump of 1 to 3 in. 25 to 75 mm. Consolidate concretes witha
27、slump less than 1 in. by vibration.NOTE 6Nonplastic concrete, such as is commonly used in themanufacture of pipe and unit masonry, is not covered by this test method.6.2 Place the concrete in the measure using the scoopdescribed in 4.7. Move the scoop around the perimeter of themeasure opening to en
28、sure an even distribution of the concretewith minimal segregation. Fill the measure in the number oflayers required by the consolidation method (6.3 or 6.4).6.3 RoddingPlace the concrete in the measure in threelayers of approximately equal volume. Rod each layer with 25strokes of the tamping rod whe
29、n nominal 0.5-ft314-L orsmaller measures are used, 50 strokes when nominal 1-ft328-L measures are used, and one stroke per 3 in.220 cm3of surface for larger measures. Rod the bottom layer through-out its depth but the rod shall not forcibly strike the bottom ofthe measure. Distribute the strokes uni
30、formly over the crosssection of the measure and for the top two layers, penetrateabout 1 in. 25 mm into the underlying layer. After each layeris rodded, tap the sides of the measure 10 to 15 times with theappropriate mallet (see 4.6) using such force so as to close anyvoids left by the tamping rod a
31、nd to release any large bubblesof air that may have been trapped. Add the final layer so as toavoid overfilling.6.4 Internal VibrationFill and vibrate the measure in twoapproximately equal layers. Place all of the concrete for eachlayer in the measure before starting vibration of that layer.Insert t
32、he vibrator at three different points for each layer. Incompacting the bottom layer, do not allow the vibrator to reston or touch the bottom or sides of the measure. In compactingthe final layer, the vibrator shall penetrate into the underlyinglayer approximately 1 in. 25 mm. Take care that the vibr
33、atoris withdrawn in such a manner that no air pockets are left in thespecimen. The duration of vibration required will depend uponthe workability of the concrete and the effectiveness of thevibrator (see Note 7). Continue vibration only long enough toachieve proper consolidation of the concrete (see
34、 Note 8).Observe a constant duration of vibration for the particular kindof concrete, vibrator, and measure involved.NOTE 7Usually, sufficient vibration has been applied as soon as theTABLE 1 Capacity of MeasuresNominal Maximum Sizeof Coarse AggregateCapacity of MeasureAin. mm ft3L1 25.0 0.2 6112 37
35、.5 0.4 11250 .5 4375 1 28412 112 2.5 706 150 3.5 100AThe indicated size of measure shall be used to test concrete containingaggregates of a nominal maximum size equal to or smaller than that listed. Theactual volume of the measure shall be at least 95 % of the nominal volume listed.C 138/C 138M 082s
36、urface of the concrete becomes relatively smooth.NOTE 8Overvibration may cause segregation and loss of appreciablequantities of intentionally entrained air.6.5 On completion of consolidation the measure must notcontain a substantial excess or deficiency of concrete. Anexcess of concrete protruding a
37、pproximately18 in. 3 mmabove the top of the mold is optimum. A small quantity ofconcrete may be added to correct a deficiency. If the measurecontains a great excess of concrete at completion of consoli-dation, remove a representative portion of the excess concretewith a trowel or scoop immediately f
38、ollowing completion ofconsolidation and before the measure is struck-off.6.6 Strike-OffAfter consolidation, strike-off the top sur-face of the concrete and finish it smoothly with the flatstrike-off plate using great care to leave the measure just levelfull. The strike-off is best accomplished by pr
39、essing thestrike-off plate on the top surface of the measure to cover abouttwo thirds of the surface and withdrawing the plate with asawing motion to finish only the area originally covered. Thenplace the plate on the top of the measure to cover the originaltwo thirds of the surface and advance it w
40、ith a vertical pressureand a sawing motion to cover the whole surface of the measureand continue to advance it until it slides completely off themeasure. Several final strokes with the inclined edge of theplate will produce a smooth finished surface.6.7 Cleaning and WeighingAfter strike-off, clean a
41、ll ex-cess concrete from the exterior of the measure and determinethe mass of the concrete and measure to an accuracy consistentwith the requirements of 4.1.7. Calculation7.1 Density (Unit Weight)Calculate the net mass of theconcrete in pounds or kilograms by subtracting the mass of themeasure, Mm,
42、from the mass of the measure filled withconcrete, Mc. Calculate the density, D,ft3or yd3,by dividingthe net mass of concrete by the volume of the measure, Vmasfollows:D 5 Mc Mm!/Vm(2)7.2 YieldCalculate the yield as follows:Yyd3! 5 M/D3 27! (3)orYm3! 5 M/D (4)7.3 Relative YieldRelative yield is the r
43、atio of the actualvolume of concrete obtained to the volume as designed for thebatch (see Note 9) calculated as follows:Ry5 Y/Yd(5)NOTE 9A value for Rygreater than 1.00 indicates an excess ofconcrete being produced whereas a value less than this indicates the batchto be “short” of its designed volum
44、e. In practice, a ratio of yield in cubicfeet per cubic yard of design concrete mixture is frequently used, forexample, 27.3 ft3/yd3.7.4 Cement ContentCalculate the actual cement contentas follows:C 5 Cb/Y (6)7.5 Air ContentCalculate the air content as follows:A 5 T 2 D!/T 3 100 (7)orA 5 Yf2 V!/Yf#
45、3 100 inch2pound units! (8)orA 5 Y 2 V!/Y 3 100 SI units! (9)8. Report8.1 Report the following information:8.1.1 Identification of concrete represented by the sample.8.1.2 Date of test.8.1.3 Volume of density measure to the nearest 0.001 ft30.01 L.8.1.4 Density (Unit Weight) to the nearest 0.1 lbs/f
46、t31.0kg/m3.8.1.5 Yield, when requested, to the nearest 0.1 yd30.1 m3.8.1.6 Relative Yield, when requested, to the nearest 0.01.8.1.7 Cement Content, when requested, to the nearest 1.0 lb0.5 kg.8.1.8 Air Content, when requested, to the nearest 0.1 per-cent.9. Precision and Bias9.1 The following estim
47、ates of precision for this test methodare based on a collection of data from various locations by theNational Ready Mixed Concrete Association.3The data repre-sent concrete mixtures with slump ranging from 3 to 6 in. 75to 150 mm and density ranging from 115 to 155 lb/ft31842 to2483 kg/m3 and include
48、d air-entrained and non air-entrainedconcrete. The study was conducted using 0.25 ft37-L and 0.5ft314-L measures.9.1.1 Single-Operator PrecisionThe single operator stan-dard deviation of density of freshly mixed concrete has beenfound to be 0.65 lb/ft310.4 kg/m3 (1s). Therefore, results oftwo proper
49、ly conducted by the same operator on the samesample of concrete should not differ by more than 1.85 lb/ft329.6 kg/m3 (d2s).9.1.2 Multi-Operator PrecisionThe multi-operator stan-dard deviation of density of freshly mixed concrete has beenfound to be 0.82 lb/ft313.1 kg/m3 (1s). Therefore, results oftwo properly conducted tests by the two operators on the samesample of concrete should not differ by more than 2.31 lb/ft337.0 kg/m3 (d2s).9.2 BiasThis test method ha
