1、Designation: C426 151C426 16Standard 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 revisi
2、on. 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 U.S. Department of Defense.1 NOTEEditorially corrected 3.2.1 in February 2016.1. S
3、cope*1.1 This test method covers a routine standardized procedure for determining the linear drying shrinkage of concrete masonryunits or related concrete units under specified accelerated drying conditions.1.2 The text of this test method references notes and footnotes that provide explanatory mate
4、rial. These notes and footnotes(excluding those in tables and figures) shall not be considered as requirements of the standard.1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematicalconversions to SI units that are provided for infor
5、mation only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulato
6、rylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C490 Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and ConcreteC1093 Practice for Accreditation of Testing Agencies for MasonryC1232 Terminology of Masonry2.2 ANSI Standard:
7、B94.11M1993 Twist Drills33. Terminology3.1 Terminology defined in Terminology C1232 shall apply for this test method.3.2 Definitions of Terms Specific to This Standard:3.2.1 linear drying shrinkage, nin this test method, the change in linear dimension of the test specimen due to drying froma saturat
8、ed condition to an equilibrium weight and length under specified accelerated drying conditions.4. Significance and Use4.1 This test method is intended to evaluate the drying shrinkage characteristics of a given unit. The results of this laboratorymethod are considered in determining concrete masonry
9、 crack control provisions.NOTE 1The testing laboratory performing this test method should be evaluated in accordance with Practice C1093.5. Apparatus5.1 Strain GaugeThe instruments for measuring linear drying shrinkage shall be so designed as to permit or provide theconditions described in 5.1.1 thr
10、ough 5.1.5.1 This test method is under the jurisdiction ofASTM Committee C15 on Manufactured Masonry Units and is the direct responsibility of Subcommittee C15.03 on ConcreteMasonry Units and Related Units.Current edition approved Dec. 1, 2015June 1, 2016. Published January 2016July 2016. Originally
11、 approved in 1958. Last previous edition approved in 20102015 asC426 10.C426 151. DOI: 10.1520/C0426-15E01.10.1520/C0426-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, re
12、fer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indica
13、tion of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be con
14、sidered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 2Strain gauges may be obtained with various gauge lengths. The 10-in. (254-mm) gauge l
15、ength is recommended for use with regular concretemasonry units, however, particular sizes of products may require other lengths. The length of the shrinkage specimen shall not be less than required fora minimum gauge length (distance between gauge plugs) of 6 in. (152.4 mm).5.1.1 A means of positiv
16、e contact with the specimen that will ensure reproducible measurements of length.5.1.2 Means for precise measurement, consisting of a dial micrometer or other measuring device graduated to read in 0.0001-in.(0.0025-mm) units, and accurate within 0.0001 in. (0.0025 mm) in any 0.0010-in. (0.025-mm) ra
17、nge, and within 0.0002 in.(0.0050-mm) in any 0.0100-in. (0.254-mm) range.5.1.3 Sufficient range to allow for small variations in the gauge 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) provides amplera
18、nge in the instrument.5.1.4 Means for checking the strain gauge at regular intervals against a standard reference bar. The standard reference bar shallbe protected from air currents by placing it inside a wooden box which should be closed except when the strain gauge is beingchecked against it.NOTE
19、4A standard reference bar shall be furnished by the manufacturer of the instrument. A standard bar of ordinary steel is satisfactory, butcorrections must be made for variations in its length due to temperature changes. When a more nearly constant datum is desired, Invar is preferablebecause of its l
20、ow coefficient of thermal expansion.5.1.5 Convenient and rapid measurement of specimens.5.2 ComparatorWhen desirable to measure specimens end to end, a comparator conforming to the requirements of PracticeC490 may be used as an alternative to the strain gauge for measuring linear drying shrinkage.5.
21、3 Gauge PlugsThe gauge plugs shall be made from metal that is resistant to corrosion. Plugs for use with strain gauges shallbe 38 to 12 in. (9.5 to 12.7 mm) in diameter and 12 6 18 (12.7 6 3.2 mm) in thickness. Plugs for use with the comparator shallconsist of 14-in. (6.4-mm) diameter stainless stee
22、l gauge studs shown in Practice C490.5.4 Drying OvenThe oven shall be reasonably airtight and provide 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 test specimens and a clearance of 1 in. (25.4 m
23、m) on all sides of each testspecimen.5.4.2 A constant, uniform temperature of 122 6 2F (50 6 0.9C) throughout the insulated cabinet attained by means of anelectrical heat source (Note 6).NOTE 6Direct heating of test specimens with the combustion products of gas or other carbonaceous fuels is not sat
24、isfactory due to the presence ofcarbon dioxide and water and their possible effect on the drying characteristics of portland cement products.5.4.3 A means of drying specimens to a condition of equilibrium with a relative humidity of 17 6 2 % (Note 7).5.4.3.1 Calcium chloride (CaCl2), if used for thi
25、s purpose, shall be in flake form. Suitable dishes or trays shall be provided togive an exposed solution area of not less than 25 in.2 for each cubic foot (5800 cm2 for each m3) of oven volume. Dishes or traysshall contain sufficient solid calcium chloride so that the crystals will be exposed above
26、the surface of the solution throughout thetest. The calcium chloride solution shall be thoroughly stirred every 24 h, and more often if necessary, to prevent the formationof lumps and crusting over.NOTE 7The air immediately above a saturated solution of calcium chloride (CaCl2) at 122F (50C) is appr
27、oximately 17 %.5.4.4 Moderate circulation of air within the oven, over and around all test specimens and the drying agent.5.5 Cooling ChamberAn airtight enclosure of sufficient capacity for cooling a minimum of three whole specimens to atemperature of 73.4 6 2F (23 6 1.1C).5.6 Immersion TankA suitab
28、le container for completely immersing three whole test specimens in water maintained at 73.4 62F (23 6 1.1C).5.7 Balance or ScaleThe balance shall be sensitive to within 0.1 % of the weight of the smallest specimen tested.6. Test Specimens6.1 The test specimens selected shall be whole units, free of
29、 visible 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 lieu ofwhole units providing they are cut lengthwise from hollow units at least 12 in. (304.8 mm) in length. Specime
30、ns to be used fortesting shall not be exposed to external heat sources.General:NOTE 8In tests of short units such as concrete brick by this method, use of a 10-in. (254-mm) Whittemore strain gauge is reported to be feasible whentwo units are butted together and joined using an epoxy resin cement to
31、form an extremely thin joint between the units. The abutting ends of the unitsshould be ground to ensure intimate contact and a thin joint; these precautions are necessary to ensure the thinnest joints practicable and thereby avoidabnormal shrinkage indications. Some laboratories have obtained satis
32、factory results using a 10-in. Whittemore strain gauge on specimens joined withunfilled epoxy cements.C426 1626.1.1 The number of specimensSpecimens shall comply with the requirements of 6.1.2 selected shouldthrough 6.1.5 consist ofthree whole unitsand the applicable requirements for the type of spe
33、cimen in 6.2 or 6.3three half face-shells. (See .Fig. 2.)6.1.2 A minimum of three specimens shall be tested.NOTE 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-m
34、m) fan assembly, as shown1 130-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
35、(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. iron pipe4 100-W porcelain light fixtures1 500-W thermostat1 24 30 112-in. (610 762 38-mm) tray, borosilicate glass or equivalent1 pr 8-in. (203-mm) hinges a
36、nd haspFIG. 1 Drying Oven Suitable for Determining Drying Shrinkage of Concrete BlockFIG. 2 View of Sawed Block Showing a Suggested Sequence of Cuts and Location of Half-Face Shell SpecimensC426 1636.1.3 Test specimens shall be representative of the lot from which they are selected. Specimens shall
37、be free of visible cracksor other structural defects, and shall not be exposed to external heat sources.6.1.4 The portions known as half face-shells should be at least 4 in. (101.6 mm) wide and should be of the same length as theface shell. Half face-shell specimens must be saw-cut fromSpecimens sha
38、ll have a minimum height of 3 in. (76.2 mm), and aminimum thickness of at least 0.75 in. (19 mm). The length of specimens shall conform to 6.1.4.1 hollowor 6.1.4.2units not lessthan 12 in. (304.8 mm) in length6.1.4.1 For full size units with a length of at least 12 in. (304.8 mm), use a test specime
39、n with a minimum length of 12 in. (304.8mm) and a gauge length of 10 in. (254 mm).6.1.4.2 For full size units with a length of less than 12 in. (304.8 mm), do one of the following: (1) use a test specimen witha minimum length of 7.5 in. (190.5 mm) and a gauge length of 6 in. (152.4 mm), or (2) butt
40、two test specimens of approximatelythe same thickness together and join with an epoxy resin cement to form a thin joint between units, and use a gauge length of 10in. (254 mm). (See Note 8.)NOTE 8In tests of short units such as concrete brick by this method, use of a 10-in. (254-mm) Whittemore strai
41、n gauge is reported to be feasible whentwo units are butted together and joined using an epoxy resin cement to form a thin joint between the units.The abutting ends of the units should be groundto ensure intimate contact and a thin joint; these precautions are necessary to ensure the thinnest joints
42、 practicable and thereby avoid abnormal shrinkageindications. Some laboratories have obtained satisfactory results using a 10-in. Whittemore strain gauge on specimens joined with unfilled epoxy cements.6.1.5 When specimens are saw-cut from larger units, sawing shall be performed in an accurate, comp
43、etent manner, subjectingthe specimen to as little saw vibration as possible. Use a diamond saw blade of proper hardness. Following cutting, residue fromthe cutting operation shall be removed prior to continuing testing (see Note 9).NOTE 9For specimens cut with a wet saw, rinsing with clean water is
44、typically sufficient for removing cutting residue. For specimens cut with a drysaw, brushing with a soft-bristle brush is typically sufficient for removing cutting residue.6.2 Concrete Masonry Units:6.2.1 Specimens shall be full-size units or portions of face shells saw-cut from full size units.6.2.
45、2 When specimens are portions of face shells, one specimen shall be removed from each of three full-size units.6.3 Other Related Units:6.3.1 For test specimens of units other than concrete masonry units, specimens shall be whole units, specimens saw-cut fromlarger units, or specimens molded specific
46、ally for testing.6.3.2 For specimens molded specifically for testing, the procedures used for molding and curing specimens shall berepresentative and consistent with the procedure used to produce the actual units represented by the specimens.6.4 Methods of Attaching Gauge Plugs to SpecimensAttach ga
47、uge plugs to specimens using one of the following procedures.6.4.1 Gauge Plug Inserted into Specimen for Strain GaugePlace a pair of gauge plugs at or near, and parallel to, the centerline in each of two opposite faces of the specimen. Drill plug holes with a drill that is slightly smaller in size t
48、han the plug diameterso as to provide a snug fit (Note 910). The depth of the holes shall be such that the exposed surface of the inserted gauge plugis approximately 18 in. (2.5 mm) below the surface of the specimen. Prior to setting of the plug, plug holes shall be dry and dustfree. After the bondi
49、ng materialagent (Note 1011) has been placed in the hole, insert the gauge plug and prick punch the plug toproper gauge length with the gauge bar provided. Wipe off excessive bonding materialagent and allow the remainder to cure. curein accordance with the bonding agent manufacturers instructions. After the bonding materialagent is sufficiently hard, cured, drillreceiving holes for strain gauge points with a No. 56 to 60 twist drill.4NOTE 10A 516-in. (7.9-mm) diameter carbide-tipped masonry drill has been found satisfa
