1、Designation: C490/C490M 11Standard Practice forUse of Apparatus for the Determination of Length Change ofHardened Cement Paste, Mortar, and Concrete1This standard is issued under the fixed designation C490/C490M; the number immediately following the designation indicates the yearof original adoption
2、 or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers the requirements for the apparatusand equipment used t
3、o prepare specimens for the determinationof length change in hardened cement paste, mortar, andconcrete, the apparatus and equipment used for the determina-tion of these length changes, and the procedures for its use.1.2 Methods for the preparation and curing of test speci-mens, conditions of testin
4、g and curing, and detailed proceduresfor calculating and reporting test results are contained inapplicable test methods.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, each
5、system shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.2. Referenced Documents2.1 ASTM Standards:2C511 Specification for Mixing Rooms, Moist Cabinets,Moist Rooms, and Water Storage Tanks Used in theTesting of Hydraulic Cem
6、ents and ConcretesC1005 Specification for Reference Masses and Devices forDetermining Mass and Volume for Use in the PhysicalTesting of Hydraulic Cements3. Terminology3.1 length changean increase or decrease in the lineardimension of a test specimen, measured along the longitudinalaxis, due to cause
7、s other than applied load.4. Significance and Use4.1 This practice is intended to provide standard require-ments for apparatus common to many test methods used inconnection with cement and concrete and standardized proce-dures for its use. The detailed requirements as to materials,mixtures, specimen
8、s, conditioning of specimens, number ofspecimens, ages at which measurements are to be made,interpretation of results, and precision and bias are left to bedealt with in specific test methods.5. Apparatus5.1 Reference Masses and Devices for Determining Massand Volume, shall conform to the requiremen
9、ts of SpecificationC1005.5.2 Molds, shall have either one or two compartments andshall be constructed as shown in Fig. 1 or Fig. 2. Molds for testspecimens used in determining the length change of cementpastes and mortars shall provide for 25 by 25 by 285-mmprisms having a 250-mm gauge length, or fo
10、r 1 by 1 by 1114in. prisms having a 10in. gauge length. Molds for testspecimens used in the length change of concretes shall providefor prisms of the desired cross section having a 10-in. or250-mm gauge length. In some routine tests, 25 by 25 by160-mm specimens with a gauge length of 125 mm, or 1 by
11、 1by 614 in. specimens with a gauge length of 5-in. arepermitted, but in case of dispute, results obtained with speci-mens of 250-mm 10-in. gauge length shall govern.5.2.1 The gauge length shall be considered as the nominallength between the innermost ends of the gauge studs. Theparts of the molds s
12、hall be tight fitting and firmly held togetherwhen assembled, and their surfaces shall be smooth and free ofpits. The molds shall be made of steel or other hard metal notreadily attacked by the cement paste, mortar, or concrete. Thesides of the molds shall be sufficiently rigid to preventspreading o
13、r warping. For the molds shown in Fig. 1, thetolerance on dimension A is 60.7 mm. For the molds shown inFig. 2, the tolerance on dimension A is 60.03 in.5.2.2 Each end plate of the mold shall be equipped to holdproperly in place, during the setting period, one of the gaugestuds shown in Fig. 1 or Fi
14、g. 2. The gauge studs shall be ofAmerican Iron and Steel Institute (AISI)3Type 316 stainlesssteel or other corrosion-resistant metal of similar hardness.1This practice is under the jurisdiction ofASTM Committee C01 on Cement andis the direct responsibility of Subcommittee C01.95 on Coordination of S
15、tandards.Current edition approved Oct. 1, 2011. Published November 2011. Originallyapproved in 1962. Last previous edition approved in 2010 as C490/C490M10.DOI: 10.1520/C0490_C0490M-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceast
16、m.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Details on this material are available from American Iron and Steel Institute(AISI), 1140 Connecticut Ave., NW, Suite 705, Washington, DC 20036, http:/www.steel.org.1*A Summar
17、y of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Gauge studs of Invar or similar metal shall be used whenspecimens are tested at widely different temperatures. Toprevent restrain
18、t of the gauge studs before demolding of thespecimen, the device for holding the gauge studs in positionshall be so arranged that, if necessary, it can be partially orcompletely released after the compaction of the paste or mortarinto place in the mold. The gauge studs shall be set so that theirprin
19、cipal axes coincide with the principal axis of the testspecimen. For the molds shown in Fig. 1, gauge studs shallextend into the specimen 17.5 6 0.5 mm and the distancebetween the inner ends of the gauge studs shall be 250.0 6 2.5mm and 250 mm shall be considered the gauge length forcalculating leng
20、th change. For the molds shown in Fig. 2,gauge studs shall extend into the specimen 0.625 6 0.025 in.and the distance between the inner ends of the gauge studs shallbe 10.00 6 0.10 in. and 10 in. shall be considered the gaugelength for calculating length change.5.3 Length Comparator, for determining
21、 length change ofspecimens, shall be designed to accommodate the size ofspecimen employed and to provide or permit a positive meansof contact with the gauge studs and the convenient and rapidobtaining of comparator readings (Note 1).5.3.1 The comparator for determining length changes ofspecimens pro
22、duced in the molds shown in Fig. 1 shall providea dial micrometer or other measuring device graduated to readin 0.002-mm units or less, accurate within 0.002 mm in any0.020-mm range, and within 0.004 mm in any 0.200-mmrange, and sufficient range (at least 8.0 mm) in the measuringdevice to allow for
23、small variations in the actual length ofvarious specimens. The terminals of the comparator shall beplane, polished and heat-treated. They shall be fitted withcollars held in place with set screws. The collars shall extend1.5 6 0.1 mm beyond the plane face of the terminal. Thecollars shall allow free
24、 rotation of the gauge stud tips that fitinside the collars and have an inside diameter no more than 0.5mm larger than the average diameter of that portion of thegauge stud tips that fit into the collars.NOTEDimension A to be specified by the purchaser.FIG. 1 Molds (SI Units)C490/C490M 112NOTE 1One
25、type of instrument that has been found satisfactory foruse with small prisms is shown in Fig. 3. A horizontal comparator shouldbe used with prisms with a cross section greater than 9 in.2or 58 cm2.5.3.2 The comparator for determining length changes ofspecimens produced in the molds shown in Fig. 2 s
26、hall providea dial micrometer or other measuring device graduated to readin 0.0001-in. units, accurate within 0.0001 in. in any 0.0010-in.range, and within 0.0002 in. in any 0.0100-in. range, andsufficient range (at least 0.3 in.) in the measuring device toallow for small variations in the actual le
27、ngth of variousspecimens. The terminals of the comparator shall be plane,polished and heat-treated. They shall be fitted with collars heldin place with set screws. The collars shall extend 0.062 60.003 in. beyond the plane face of the terminal. The collarsshall allow free rotation of the gauge stud
28、tips that fit inside thecollars and have an inside diameter no more than 0.02 in. largerthan the average diameter of that portion of the gauge stud tipsthat fit into the collars.5.3.3 The design shall provide a means for checking themeasuring device against a reference bar at regular intervals.5.4 R
29、eference Bar, shall have an overall length of 295 6 3.0mm or 170 6 3.0 mm 1158 618 in. or 658 618 in.,whichever is appropriate for the specimen in use. The bar shallbe of a steel alloy having a coefficient of thermal expansion notgreater than two millionths per degree Celsius. Each end of thereferen
30、ce bar shall be fitted with heat treated, hardened, andpolished tips machined to the same shape as the contact end ofthe gauge studs used in test specimens. That portion of the barthat extends into the comparators collar shall have a diameterof 6 6 0.25 mm 0.250 6 0.010 in., and the length of thatpo
31、rtion shall extend beyond the depth of the collar. Except forthe tips, which are attached after heat treatment, no part of thereference bar shall be heat treated (Note 2). The central 100mm 4 in. of the length of the reference bar shall be coveredby a rubber tube with a wall at least 3 mm 18 in. thi
32、ck tominimize the effect of temperature change during handling.The reference bar shall be provided near one end with apositioning mark.FIG. 2 Molds (Inch-Pound Units)C490/C490M 113NOTE 2Alloys such as invar lose their low coefficient of thermalexpansion properties when heat treated.5.5 Check and doc
33、ument the bar mold dimensions, gaugestud projection into the mold interior, length comparator, andlength measuring device for conformance to the design anddimensional requirements of this specification at least every212 years.6. Procedure6.1 Preparation of MoldsPrior to the molding of speci-mens, th
34、e outside joints of the mold and the contact lines of themold and base plate shall be sealed to prevent loss of mixingwater from a freshly molded specimen. Thinly cover theinterior surfaces of the mold with mineral oil. After thisoperation, set the gauge studs, taking care to keep them clean,and fre
35、e of oil, grease, and foreign matter.6.2 Use of Reference BarFor each reference readingtaken, place the reference bar into the comparator with thepositioning mark in the same orientation. With the bar in thecomparator, rotate it slowly through at least one completerevolution while the gauge reading
36、is being taken. Record theminimum (shortest) gauge reading (Note 3). Monitor andrecord the room temperature in which the comparator is used.Use the reference bar when the temperature difference is morethan 6 1.0 C of the previous use of the comparator apparatus,and at least at the beginning and end
37、of the specimen readingsmade within a half day.NOTE 3The reference bar is used in the comparator to correct forchanges occurring to the comparator apparatus and gauge that affectlength readings. The reference bar is always placed in the same orientationin the comparator apparatus to minimize changes
38、 in reading due todifferences in contact surfaces. Frequent use of the reference bar can resultin significant wear of the tips, which affects the indicated length of the bar.Appropriate steps should be taken to monitor reference bar condition andreplace as needed.NOTE 4The equation given in the sect
39、ion on calculation of lengthchange contemplates that a comparator reading for the reference bar willbe recorded each time the reference bar is used and a difference calculatedfor each test specimen reading. Alternatively, the dial gauge setting can bereset, if necessary, to its original setting with
40、 the reference bar in placeeach time the reference bar is read. Doing so simplifies the calculation oflength change by canceling the comparator reading of the reference barfrom the values of Lxand Li. If this procedure is used, care should be takento ensure that the dial set screw is tightened adequ
41、ately each time the dialis reset.6.3 Obtaining Comparator ReadingsRotate specimensslowly in the measuring instrument while the comparatorreading is being taken. Record the minimum reading of the dialif the rotation causes a change in the dial reading. Placespecimens in the instrument with the same e
42、nd up each time acomparator reading is taken.6.3.1 Obtaining Comparator Readings of Specimens StoredMoistClean the hole in the base of the comparator into whichthe gauge stud on the lower end of the bar fits before and afterevery reading. Read and record the comparator indication ofthe length of the
43、 reference bar and temperature of the room inwhich the comparator is being used (Note 4). Take one bar outof immersion, blot only around the pins, put the bar in thecomparator, read, and record the indication (Note 5). Returnthe bar to immersion. Take out the second bar and treat it in alike manner.
44、 Return the second bar to immersion and record thereading. Continue the procedure until all bars have been read,returned to immersion, and the readings recorded. After read-ing the last bar, read and record the reference-bar indicationand temperature of the room in which the comparator wasused. Comp
45、are the two reference bar readings. If the differencein the reference bar readings is greater than 0.010 mm 0.0004in, then use the average of the beginning and ending values forthe Lxand Lifactors in the formula in the calculations section.Otherwise use the beginning reading only.NOTE 5The purpose o
46、f the minimal blotting of the pins and noblotting of the bars is to avoid drying and shrinkage of the bars. It has beenobserved that if the pins are blotted, and the bar placed in the comparatorand the dial read, and the bar is then wiped gently with a dry cloth, the barwill shrink measurably. There
47、fore, drying should be minimized.7. Calculation of Length Change7.1 Calculate the length change at any age as follows:L 5Lx2 Li!G3 100where:L = change in length at x age, %,Lx= comparator reading of specimen at x age minuscomparator reading of reference bar at x age; inmillimetres when using Fig. 1
48、apparatus, in incheswhen using Fig. 2 apparatus,FIG. 3 Type of Suitable Apparatus for Measurement of LengthChangesC490/C490M 114Li= initial comparator reading of specimen minus com-parator reading of reference bar at that same time; inmillimetres when using Fig. 1 apparatus, in incheswhen using Fig.
49、 2 apparatus, andG = nominal gauge length, 250 mm when using Fig. 1apparatus, 10 in. when using Fig. 2 apparatus.7.2 Calculate length change values for each specimen to thenearest 0.001 % and report averages to the nearest 0.01 %.8. Temperature, Humidity, and Time8.1 Molding RoomThe temperature of the molding roomand dry materials shall be maintained between 23.0 6 4 C.The relative humidity shall be not less than 50 %. Thetemperature of the mixing water shall be 23.0 6 2.0 C.8.2 Moist Storage FacilityThe temperature and humidityof the air
