1、Designation: C426 10C426 15Standard 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 revisio
2、n. 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. Scope*1.1 This test method covers a routine standardi
3、zed procedure for determining the linear drying shrinkage of concrete masonryunits or related concrete units under specified accelerated drying conditions.1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematicalconversions to SI units
4、 that are provided for information only and are not considered standard.1.3 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 t
5、he applicability of regulatorylimitations 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
6、of Masonry2.2 ANSI Standard:B94.11M1993 Twist Drills33. Terminology3.1 Terminology defined in Terminology C1232 shall apply for this test method.3.2 Definitions:Definitions of Terms Specific to This Standard:3.2.1 linear drying shrinkagein this test method, the change in linear dimension of the test
7、 specimen due to drying from asaturated 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 consi
8、dered in determining concrete masonry 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
9、 theconditions 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 regular concretemasonry units, however, particular sizes of products may require other lengths. The length of the shrinkage spe
10、cimen shall not be less than required fora minimum gauge length (distance between gauge plugs) of 6 in. (152.4 mm).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 Rela
11、ted Units.Current edition approved Dec. 1, 2010Dec. 1, 2015. Published December 2010January 2016. Originally approved in 1958. Last previous edition approved in 20072010as C426 07.C426 10. DOI: 10.1520/C0426-10.10.1520/C0426-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or
12、contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer 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
13、 document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication 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 edition
14、s as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered 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. U
15、nited States15.1.1 A means of positive 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. (0.002
16、5 mm) in any 0.0010-in. (0.025-mm) range, 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
17、 in. (5.1 or 7.6 mm) provides amplerange 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 g
18、auge is beingchecked against it.NOTE 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
19、, Invar is preferablebecause of its low 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
20、 measuring linear drying shrinkage.5.3 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
21、-in. (6.4-mm) diameter stainless steel 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 speci
22、mens and a clearance of 1 in. (25.4 mm) 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 o
23、r other carbonaceous fuels is not satisfactory 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 Calc
24、ium chloride (CaCl2), if used for this 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 tha
25、t the crystals will be exposed above 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 c
26、hloride (CaCl2) at 122F (50C) is approximately 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 (
27、23 6 1.1C).5.6 Immersion TankA suitable 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 s
28、elected shall be whole units, free of 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
29、 12 in. (304.8 mm) in length. Specimens to be used fortesting 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 reported to be feasible whentwo units are butted together and joined us
30、ing an epoxy resin cement to 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 lab
31、oratories have obtained satisfactory results using a 10-in. Whittemore strain gauge on specimens joined withunfilled epoxy cements.6.1.1 The number of specimens selected should consist of three whole units or three half face-shells. (See Fig. 2.)6.1.2 The portions known as half face-shells should be
32、 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 from hollow units not less than 12 in. (304.8 mm) in length.C426 1526.2 Methods of Attaching Gauge Plugs to Specimens: SpecimensAttach gauge plugs to specimens using one of th
33、e followingprocedures.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-mm) fan assembly, as shown1 130-hp (25-W) shaded-pole, fan-cooled, stud-mounted electri
34、c 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 m2) Inner cover, 38-in. (9.5-mm) asbestos board or equivalent1 Heat baffle, 25 by
35、 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 and haspFIG. 1 Drying Oven Suitable for Determining Drying Shrinkage of Concrete BlockF
36、IG. 2 View of Sawed Block Showing a Suggested Sequence of Cuts and Location of Half-Face Shell SpecimensC426 1536.2.1 Gauge Plug Inserts for Use with Strain GaugesInserted into Specimen for Strain GaugePlace a pair of gauge plugsat or near, and parallel to, the center line in each of two opposite fa
37、ces of the specimen. Drill plug holes with a drill that is slightlysmaller in size than the plug diameter so as to provide a snug fit (Note 9). The depth of the holes shall be such that the exposedsurface of the inserted gauge plug is approximately 18 in. (2.5 mm) below the surface of the specimen.
38、Prior to setting of the plug,plug holes shall be dry and dust free. After the bonding material (Note 10) has been placed in the hole, insert the gauge plug andprick punch the plug to proper gauge length with the gauge bar provided. Wipe off excessive bonding material and allow theremainder to cure.
39、After the bonding material is sufficiently hard, drill receiving holes for strain gauge points with a No. 56 to 60twist drill.4NOTE 9A 516-in. (7.9-mm) diameter carbide-tipped masonry drill has been found satisfactory for gauge plugs 38 in. (9.5 mm) in diameter.NOTE 10A number of bonding agents have
40、 been reported satisfactory for setting gauge plugs. Tests to determine the effect of water immersion andsubsequent drying on the bonding agents adhesion should be made prior to use. Satisfactory results have been reported with the use of aluminum puttyfor both drilled gauge plugs as well as surface
41、-mounted plugs.6.2.2 Gauge Plugs Surface Mounted to Specimen for Strain GaugeDrill receiving holes in gauge plugs for strain gauge pointsprior to attachment of gauge plugs. Place a pair of gauge plugs at or near, and parallel to, the center line of each of the two oppositefaces of the specimen. Atta
42、ch gauge plugs with a bonding agent (Note 10) using the strain gauge punch bar or other convenienttemplate to set gauge holes the proper distance apart. Gauge plugs shall be approximately level with each other with respect tothe surface of the specimen.6.3 Inserts Gauge Plugs for Comparator Measurem
43、entsOn opposite ends of the test specimen, mount spherically shapedgauge plugs, for use with the comparator (see 5.2). Drill a shallow recess (Note 11) at the desired location using a drill slightlyless in size than the plug diameter. Fill the recess with a bonding agent, and firmly press the plug i
44、nto position, taking care thatthe bonding agent extends slightly above the level of the center of the sphere. After the bonding agent is sufficiently hard, cleanexcess material from the exposed portion of the gauge plug.NOTE 11Satisfactory results without a drilled recess have been reported with the
45、 use of quick-setting bonding agents. Aluminum putty has beendemonstrated to perform well in this test as an adhesive to adhere gauge plugs to the surface of test specimens.7. Procedure7.1 Immerse specimens in water at 73.4 6 2F (23 6 1.1C) for 486 48 6 2 h.hours.7.2 Take the initial reading of spec
46、imen length, at saturation, with the unit positioned in the water tank so that its gauge lineis about at the level of the water surface to avoid error due to cooling by evaporation. Take accompanying length readings of thestandard reference bar. (See 8.1 and 8.2 for methods of adjusting and correcti
47、ng length readings.) Record the temperature of thewater as Tx.7.3 Weigh and record the saturated surface-dry weight of the test specimen by draining the test specimen for 1 min 6 5 s overa 38-in. (9.5-mm) (or larger) mesh and removing visible surface water by blotting with a damp cloth.7.4 Within 48
48、 h after the specimens have been removed from the water, place them in the drying oven described in 5.4. Duringthis period of up to 48 h, the specimens shall be stored continuously in air at a temperature of 75 6 15F (24 6 8C) and a relativehumidity of less than 80 % (Note 12). To ensure uniformity
49、of drying, the individual specimens should be rotated to differentpositions in the drying oven each time readings are taken.NOTE 12Reports have indicated that moisture is exuded faster by some masonry units during the early part of the drying period than can be absorbedby the calcium chloride solution, causing condensation to form on the interior surfaces of the oven.7.5 At the end of 5 days of drying, including any period of preliminary drying in air up to 48 h, remove shrinkage specimensfrom the drying oven and
