1、Designation: C426 10Standard Test Method forLinear Drying Shrinkage of Concrete Masonry Units1This standard is issued under the fixed designation C426; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu
2、mber 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 a routine standardized proce-du
3、re for determining the linear drying shrinkage of concretemasonry units or related concrete units under specified accel-erated drying conditions.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are p
4、rovided for information onlyand are not considered standard.1.3 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-priate safety and health practices and determine the applica-b
5、ility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C490 Practice for Use of Apparatus for the Determinationof Length Change of Hardened Cement Paste, Mortar, andConcreteC1093 Practice for Accreditation of Testing Agencies forMasonry2.2 ANSI Standard:B94.11M1993 T
6、wist Drills33. Terminology3.1 Definition:3.1.1 linear drying shrinkagein this test method, thechange in linear dimension of the test specimen due to dryingfrom a saturated condition to an equilibrium weight and lengthunder specified accelerated drying conditions.4. Significance and Use4.1 This test
7、method is intended to evaluate the dryingshrinkage characteristics of a given unit. The results of thislaboratory method are considered in determining concretemasonry crack control provisions.NOTE 1The testing laboratory performing this test method should beevaluated in accordance with Practice C109
8、3.5. Apparatus5.1 Strain GaugeThe instruments for measuring lineardrying shrinkage shall be so designed as to permit or providethe conditions described in 5.1.1 through 5.1.5.NOTE 2Strain gauges may be obtained with various gauge lengths.The 10-in. (254-mm) gauge length is recommended for use with r
9、egularconcrete masonry units, however, particular sizes of products may requireother lengths. The length of the shrinkage specimen shall not be less thanrequired for a minimum gauge length (distance between gauge plugs) of6 in. (152.4 mm).5.1.1 A means of positive contact with the specimen thatwill
10、ensure reproducible measurements of length.5.1.2 Means for precise measurement, consisting of a dialmicrometer or other measuring device graduated to read in0.0001-in. (0.0025-mm) units, and accurate within 0.0001 in.(0.0025 mm) in any 0.0010-in. (0.025-mm) range, and within0.0002 in. (0.0050-mm) in
11、 any 0.0100-in. (0.254-mm) range.5.1.3 Sufficient range to allow for small variations in thegauge lengths.NOTE 3If the shrinkage reference points are set carefully to position,a dial micrometer with a travel of 0.2 or 0.3 in. (5.1 or 7.6 mm) providesample range in the instrument.5.1.4 Means for chec
12、king the strain gauge at regular inter-vals against a standard reference bar. The standard referencebar shall be protected from air currents by placing it inside awooden box which should be closed except when the straingauge is being checked against it.NOTE 4A standard reference bar shall be furnish
13、ed by the manufac-turer of the instrument.Astandard bar of ordinary steel is satisfactory, but1This test method is under the jurisdiction of ASTM Committee C15 onManufactured Masonry Units and is the direct responsibility of SubcommitteeC15.03 on Concrete Masonry Units and Related Units.Current edit
14、ion approved Dec. 1, 2010. Published December 2010. Originallyapproved in 1958. Last previous edition approved in 2007 as C426 07. DOI:10.1520/C0426-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMSta
15、ndards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM
16、International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.corrections must be made for variations in its length due to temperaturechanges. When a more nearly constant datum is desired, Invar ispreferable because of its low coefficient of thermal expansion.5.1
17、.5 Convenient and rapid measurement of specimens.5.2 ComparatorWhen desirable to measure specimensend to end, a comparator conforming to the requirements ofPractice C490 may be used as an alternative to the strain gaugefor measuring linear drying shrinkage.5.3 Gauge PlugsThe gauge plugs shall be mad
18、e frommetal that is resistant to corrosion. Plugs for use with straingauges shall be38 to12 in. (9.5 to 12.7 mm) in diameter and12 618 (12.7 6 3.2 mm) in thickness. Plugs for use with thecomparator shall consist of14-in. (6.4-mm) diameter stainlesssteel gauge studs shown in Practice C490.5.4 Drying
19、OvenThe oven shall be reasonably airtight andprovide the features described in 5.4.1 through 5.4.4.NOTE 5One suggested oven construction is shown in Fig. 1.5.4.1 A minimum storage capacity of three whole testspecimens and a clearance of 1 in. (25.4 mm) on all sides ofeach test specimen.5.4.2 A const
20、ant, uniform temperature of 122 6 2F (50 60.9C) throughout the insulated cabinet attained by means ofan electrical heat source (Note 6).NOTE 6Direct heating of test specimens with the combustion prod-ucts of gas or other carbonaceous fuels is not satisfactory due to thepresence of carbon dioxide and
21、 water and their possible effect on thedrying characteristics of portland cement products.5.4.3 A means of drying specimens to a condition ofequilibrium with a relative humidity of 17 6 2%(Note 7).5.4.3.1 Calcium chloride (CaCl2), if used for this purpose,shall be in flake form. Suitable dishes or t
22、rays shall be providedto give an exposed solution area of not less than 25 in.2for eachcubic foot (5800 cm2for each m3) of oven volume. Dishes ortrays shall contain sufficient solid calcium chloride so that thecrystals will be exposed above the surface of the solutionNOTE 1Provide access to heaters.
23、NOTE 2Insulating fill is recommended in cabinets having outer covers of sheet metalNOTE 3The following materials are required:Quantity Description1 5-in. (127-mm) fan assembly, as shown1130-hp (25-W) shaded-pole, fan-cooled, stud-mounted electric motor75 ft (22.9 m) 1-in. (25.4-mm) angle, steel or a
24、luminum60 ft2(5.6 m2) Outer cover,12-in. (12.7-mm) plywood or equivalent, faced with sheet metal or other material to provide a positive vapor barrier60 ft2(5.6 m2) Inner cover,38-in. (9.5-mm) asbestos board or equivalent1 Heat baffle, 25 by 34-in. (635 by 864-mm), sheet metal16 ft (4.8 m)12-in. iro
25、n pipe4 100-W porcelain light fixtures1 500-W thermostat1243 30 3 112-in. (610 3 762 3 38-mm) tray, borosilicate glass or equivalent1 pr 8-in. (203-mm) hinges and haspFIG. 1 Drying Oven Suitable for Determining Drying Shrinkage of Concrete BlockC426 102throughout the test. The calcium chloride solut
26、ion shall bethoroughly stirred every 24 h, and more often if necessary, toprevent the formation of lumps and crusting over.NOTE 7The air immediately above a saturated solution of calciumchloride (CaCl2) at 122F (50C) is approximately 17 %.5.4.4 Moderate circulation of air within the oven, over andar
27、ound all test specimens and the drying agent.5.5 Cooling ChamberAn airtight enclosure of sufficientcapacity for cooling a minimum of three whole specimens to atemperature of 73.4 6 2F (23 6 1.1C).5.6 Immersion TankA suitable container for completelyimmersing three whole test specimens in water maint
28、ained at73.4 6 2F (23 6 1.1C).5.7 Balance or ScaleThe balance shall be sensitive towithin 0.1 % of the weight of the smallest specimen tested.6. Test Specimens6.1 The test specimens selected shall be whole units, free ofvisible cracks or other structural defects, which shall berepresentative of the
29、lot from which they are selected (Note 8).Portions of face shells (see 6.1.1) may be used for test in lieuof whole units providing they are cut lengthwise from hollowunits at least 12 in. (304.8 mm) in length. Specimens to be usedfor testing shall not be exposed to external heat sources.NOTE 8In tes
30、ts of short units such as concrete brick by this method,use of a 10-in. (254-mm) Whittemore strain gauge is reported to befeasible when two units are butted together and joined using an epoxyresin cement to form an extremely thin joint between the units. Theabutting ends of the units should be groun
31、d to ensure intimate contact anda thin joint; these precautions are necessary to ensure the thinnest jointspracticable and thereby avoid abnormal shrinkage indications. Somelaboratories have obtained satisfactory results using a 10-in. Whittemorestrain gauge on specimens joined with unfilled epoxy c
32、ements.6.1.1 The number of specimens selected should consist ofthree whole units or three half face-shells. (See Fig. 2.)6.1.2 The portions known as half face-shells should be atleast 4 in. (101.6 mm) wide and should be of the same lengthas the face shell. Half face-shell specimens must be saw-cutfr
33、om hollow units not less than 12 in. (304.8 mm) in length.6.2 Methods of Attaching Gauge Plugs to Specimens:6.2.1 Gauge Plug Inserts for Use with Strain GaugesPlace a pair of gauge plugs at or near, and parallel to, thecenter line in each of two opposite faces of the specimen. Drillplug holes with a
34、 drill that is slightly smaller in size than theplug diameter so as to provide a snug fit (Note 9). The depth ofthe holes shall be such that the exposed surface of the insertedgauge plug is approximately18 in. (2.5 mm) below the surfaceof the specimen. Prior to setting of the plug, plug holes shall
35、bedry and dust free. After the bonding material (Note 10) hasbeen placed in the hole, insert the gauge plug and prick punchthe plug to proper gauge length with the gauge bar provided.Wipe off excessive bonding material and allow the remainderto cure. After the bonding material is sufficiently hard,
36、drillreceiving holes for strain gauge points with a No. 56 to 60 twistdrill.4NOTE 9A516-in. (7.9-mm) diameter carbide-tipped masonry drill hasbeen found satisfactory for gauge plugs38 in. (9.5 mm) in diameter.NOTE 10Anumber of bonding agents have been reported satisfactoryfor setting gauge plugs. Te
37、sts to determine the effect of water immersionand subsequent drying on the bonding agents adhesion should be madeprior to use.6.2.2 Drill receiving holes in gauge plugs for strain gaugepoints prior to attachment of gauge plugs. Attach gauge plugswith a bonding agent (Note 10) using the strain gauge
38、punchbar or other convenient template to set gauge holes the properdistance apart.6.3 Inserts for Comparator MeasurementsOn oppositeends of the test specimen, mount spherically shaped gaugeplugs, for use with the comparator (see 5.2). Drill a shallowrecess (Note 11) at the desired location using a d
39、rill slightlyless in size than the plug diameter. Fill the recess with abonding agent, and firmly press the plug into position, takingcare that the bonding agent extends slightly above the level ofthe center of the sphere. After the bonding agent is sufficientlyhard, clean excess material from the e
40、xposed portion of thegauge plug.NOTE 11Satisfactory results without a drilled recess have beenreported with the use of quick-setting bonding agents. Aluminum puttyhas been demonstrated to perform well in this test as an adhesive to adheregauge plugs to the surface of test specimens.4Detailed require
41、ments for these twist drills are given in the American NationalStandard for Twist Drills (ANSI B5.10).FIG. 2 View of Sawed Block Showing a Suggested Sequence of Cuts and Location of Half-Face Shell SpecimensC426 1037. Procedure7.1 Immerse specimens in water at 73.4 6 2F (23 6 1.1C)for 486 2h.7.2 Tak
42、e the initial reading of specimen length, at satura-tion, with the unit positioned in the water tank so that its gaugeline is about at the level of the water surface to avoid error dueto cooling by evaporation. Take accompanying length readingsof the standard reference bar. (See 8.1 and 8.2 for meth
43、ods ofadjusting and correcting length readings.) Record the tempera-ture of the water as Tx.7.3 Weigh and record the saturated surface-dry weight ofthe test specimen by draining the test specimen for 1 min 6 5s over a38-in. (9.5-mm) (or larger) mesh and removing visiblesurface water by blotting with
44、 a damp cloth.7.4 Within 48 h after the specimens have been removedfrom the water, place them in the drying oven described in 5.4.During this period of up to 48 h, the specimens shall be storedcontinuously in air at a temperature of 75 6 15F (24 6 8C)and a relative humidity of less than 80 % (Note 1
45、2). To ensureuniformity of drying, the individual specimens should berotated to different positions in the drying oven each timereadings are taken.NOTE 12Reports have indicated that moisture is exuded faster bysome masonry units during the early part of the drying period than can beabsorbed by the c
46、alcium chloride solution, causing condensation to formon the interior surfaces of the oven.7.5 At the end of 5 days of drying, including any period ofpreliminary drying in air up to 48 h, remove shrinkagespecimens from the drying oven and cool to 73.4 6 2F (23 61.1C) within8h(Note 13). Following coo
47、ling, record thetemperature of the cooling chamber of Tx, remove eachspecimen from the cooling container and immediately takespecimen length readings. Take accompanying length readingsof the standard reference bar. Weigh the specimens. The airtemperature of the laboratory at the time length readings
48、 aremade on the specimens shall be 73.4 6 5F (23 6 2.8C).NOTE 13Use a cooling chamber consisting of a steel, drum-typecontainer equipped with a ring-sealed, rubber-gasketed type cover. Thedrum cover should be equipped with a thermometer, the bulb of which isin the proximity of the uppermost test spe
49、cimen. The drum must be storedin a temperature-controlled room in order that its final equilibriumtemperature will be 73.4 6 2F (23 6 1.1C). Length measurements madeat temperatures other than 73.4F (23C) shall be corrected as shown in8.1.7.6 Return test specimens to the drying oven for a secondperiod of drying. The duration of the second, and subsequent,oven drying periods shall be 44 6 4 h. Following the secondperiod of drying, repeat cooling, length readings, and weightdeterminations as specified in 7.5.7.7 Continue
