1、Designation: C426 151Standard 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 n
2、umber 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 U.S. Department of Defense.1NOTEEditorially corrected 3.2.1 in February 2016.1. Scope*1.1
3、 This test method covers a routine standardized proce-dure 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 parent
4、heses are mathematicalconversions to SI units that are provided 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
5、 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C490 Practice for Use ofApparatus for the Determination ofLength Change of Hardened Cement Paste, Mortar, andConcreteC1093 Practice for Accreditation of Tes
6、ting Agencies forMasonryC1232 Terminology of Masonry2.2 ANSI Standard:B94.11M1993 Twist Drills33. Terminology3.1 Terminology defined in Terminology C1232 shall applyfor this test method.3.2 Definitions of Terms Specific to This Standard:3.2.1 linear drying shrinkage, nin this test method, thechange
7、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 method is intended to evaluate the dryingshrinkage characteristics of a given unit. The results of th
8、islaboratory method are considered in determining concretemasonry crack control provisions.NOTE 1The testing laboratory performing this test method should beevaluated in accordance with Practice C1093.5. Apparatus5.1 Strain GaugeThe instruments for measuring lineardrying shrinkage shall be so design
9、ed 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 regularconcrete masonry units, however, particular sizes of products may requireother lengths. The len
10、gth 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 ensure reproducible measurements of length.5.1.2 Means for precise measurement, consisting of a dialm
11、icrometer 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 any 0.0100-in. (0.254-mm) range.5.1.3 Sufficient range to allow for small variations in thegauge len
12、gths.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 checking the strain gauge at regular inter-vals against a standard reference bar. The standard referenceb
13、ar 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.1This test method is under the jurisdiction of ASTM Committee C15 onManufactured Masonry Units and is the direct responsibility of SubcommitteeC15.0
14、3 on Concrete Masonry Units and Related Units.Current edition approved Dec. 1, 2015. Published January 2016. Originallyapproved in 1958. Last previous edition approved in 2010 as C426 10. DOI:10.1520/C0426-15E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
15、tomer Service at serviceastm.org. For Annual Book of ASTMStandards 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.*A Summary of Changes
16、section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 4A standard reference bar shall be furnished by the manufac-turer of the instrument.Astandard bar of ordinary steel is satisfactory, butco
17、rrections 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.5.1.5 Convenient and rapid measurement of specimens.5.2 ComparatorWhen desirable to measure specimensend
18、 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 made frommetal that is resistant to corrosion. Plugs for use with straingauges shall be38 to12 in. (9.5
19、to 12.7 mm) in diameter and12618 (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 OvenThe oven shall be reasonably airtight andprovide the features described in 5.4.1 through 5.4.4.NOT
20、E 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 constant, uniform temperature of 122 6 2F (50 60.9C) throughout the insulated cabinet attained by means ofa
21、n electrical heat source (Note 6).NOTE 6Direct heating of test specimens with the combustion productsof gas or other carbonaceous fuels is not satisfactory due to the presenceof carbon dioxide and water and their possible effect on the dryingcharacteristics of portland cement products.5.4.3 A means
22、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 trays shall be providedto give an exposed solution area of not less than 25 in.2for eachcubic foot (5800
23、cm2for each m3) of oven volume. Dishes ortrays shall contain sufficient solid calcium chloride so that theNOTE 1Provide access to heaters.NOTE 2Insulating fill is recommended in cabinets having outer covers of sheet metalNOTE 3The following materials are required:Quantity Description1 5-in. (127-mm)
24、 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 aluminum60 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 m
25、2) 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. iron pipe4 100-W porcelain light fixtures1 500-W thermostat1 2430112-in. (610 762 38-mm) tray, borosilicate glass or equivalent1 pr 8-in. (203-mm) hinges and haspFIG
26、. 1 Drying Oven Suitable for Determining Drying Shrinkage of Concrete BlockC426 1512crystals will be exposed above the surface of the solutionthroughout the test. The calcium chloride solution shall bethoroughly stirred every 24 h, and more often if necessary, toprevent the formation of lumps and cr
27、usting 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 andaround all test specimens and the drying agent.5.5 Cooling ChamberAn airtight enclosure of sufficientcapacity for
28、 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 maintained at73.4 6 2F (23 6 1.1C).5.7 Balance or ScaleThe balance shall be sensitive towithin 0.1 % of the weight o
29、f 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 lot from which they are selected (Note 8).Portions of face shells (see 6.1.1) may be used for test in lieuof wh
30、ole 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 tests of short units such as concrete brick by this method,use of a 10-in. (254-mm) Whittemore strain gauge is rep
31、orted 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 ground to ensure intimate contact anda thin joint; these precautions are necessary to ensure the thinnest jointsprac
32、ticable and thereby avoid abnormal shrinkage indications. Somelaboratories have obtained satisfactory results using a 10-in. Whittemorestrain gauge on specimens joined with unfilled epoxy cements.6.1.1 The number of specimens selected should consist ofthree whole units or three half face-shells. (Se
33、e 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-cutfrom hollow units not less than 12 in. (304.8 mm) in length.6.2 Methods of Attaching Gauge Plugs to SpecimensAtta
34、ch gauge plugs to specimens using one of the followingprocedures.6.2.1 Gauge Plug Inserted into Specimen for StrainGaugePlace a pair of gauge plugs at or near, and parallel to,the center line in each of two opposite faces of the specimen.Drill plug holes with a drill that is slightly smaller in size
35、 thanthe plug diameter so as to provide a snug fit (Note 9).The depthof the holes shall be such that the exposed surface of theinserted gauge plug is approximately18 in. (2.5 mm) below thesurface of the specimen. Prior to setting of the plug, plug holesshall be dry and dust free.After the bonding ma
36、terial (Note 10)has been placed in the hole, insert the gauge plug and prickpunch the plug to proper gauge length with the gauge barprovided. Wipe off excessive bonding material and allow theremainder to cure. After the bonding material is sufficientlyhard, drill receiving holes for strain gauge poi
37、nts with a No. 56to 60 twist drill.4NOTE 9A516-in. (7.9-mm) diameter carbide-tipped masonry drill hasbeen found satisfactory for gauge plugs38 in. (9.5 mm) in diameter.NOTE 10A number of bonding agents have been reported satisfactoryfor setting gauge plugs. Tests to determine the effect of water imm
38、ersionand subsequent drying on the bonding agents adhesion should be madeprior to use. Satisfactory results have been reported with the use ofaluminum putty for both drilled gauge plugs as well as surface-mountedplugs.6.2.2 Gauge Plugs Surface Mounted to Specimen for StrainGaugeDrill receiving holes
39、 in gauge plugs for strain gaugepoints prior to attachment of gauge plugs. Place a pair of gaugeplugs at or near, and parallel to, the center line of each of thetwo opposite faces of the specimen. Attach gauge plugs with abonding agent (Note 10) using the strain gauge punch bar orother convenient te
40、mplate to set gauge holes the properdistance apart. Gauge plugs shall be approximately level witheach other with respect to the surface of the specimen.6.3 Gauge Plugs for Comparator MeasurementsOn oppo-site ends of the test specimen, mount spherically shaped gaugeplugs, for use with the comparator
41、(see 5.2). Drill a shallow4Detailed requirements 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 1513recess (Note 11) at the desired location
42、using a drill 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 f
43、rom the exposed 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.7. Proce
44、dure7.1 Immerse specimens in water at 73.4 6 2F (23 6 1.1C)for 48 6 2 hours.7.2 Take the initial reading of specimen length, atsaturation, with the unit positioned in the water tank so that itsgauge line is about at the level of the water surface to avoiderror due to cooling by evaporation. Take acc
45、ompanying lengthreadings of the standard reference bar. (See 8.1 and 8.2 formethods of adjusting and correcting length readings.) Recordthe temperature 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-i
46、n. (9.5-mm) (or larger) mesh and removing visiblesurface water by blotting with 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 tem
47、perature of 75 6 15F (24 6 8C)and a relative humidity of less than 80 % (Note 12). 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 masonr
48、y units during the early part of the drying period than can beabsorbed by the calcium 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 th
49、e drying oven and cool to 73.4 6 2F (23 61.1C) within8h(Note 13). Following cooling, 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 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
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