1、Designation: C457/C457M 11Standard Test Method forMicroscopical Determination of Parameters of the Air-VoidSystem in Hardened Concrete1This standard is issued under the fixed designation C457/C457M; the number immediately following the designation indicates the yearof original adoption or, in the ca
2、se 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 test method describes procedures for microscopicaldeterminations of the air content
3、of hardened concrete and ofthe specific surface, void frequency, spacing factor, and paste-air ratio of the air-void system in hardened concrete (1).2Twoprocedures are described:1.1.1 Procedure A, the linear-traverse method (2, 3).1.1.2 Procedure B, the modified point-count method (3, 4, 5,6).1.2 Th
4、is test method is based on prescribed procedures thatare applied to sawed and lapped sections of specimens ofconcrete from the field or laboratory.1.3 It is intended to outline the principles of this test methodand to establish standards for its adequate performance but notto describe in detail all
5、the possible variations that might beused to accomplish the objectives of this test method.1.4 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, eachsystem shall be used independ
6、ently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.5 This standard does not purport to address all of thesafety concerns associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth prac
7、tices and determine the applicability of regulatorylimitations prior to use. For specific hazard statements see 8.3and 10.1.2. Referenced Documents2.1 ASTM Standards:3C42/C42M Test Method for Obtaining and Testing DrilledCores and Sawed Beams of ConcreteC125 Terminology Relating to Concrete and Conc
8、rete Ag-gregatesC138/C138M Test Method for Density (Unit Weight),Yield, and Air Content (Gravimetric) of ConcreteC173/C173M Test Method for Air Content of FreshlyMixed Concrete by the Volumetric MethodC231 Test Method for Air Content of Freshly Mixed Con-crete by the Pressure MethodC666/C666M Test M
9、ethod for Resistance of Concrete toRapid Freezing and ThawingC670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsC672/C672M Test Method for Scaling Resistance of Con-crete Surfaces Exposed to Deicing ChemicalsC823 Practice for Examination and Sampling
10、of HardenedConcrete in ConstructionsC856 Practice for Petrographic Examination of HardenedConcreteD92 Test Method for Flash and Fire Points by ClevelandOpen Cup Tester2.2 American Concrete Institute Standards:201.2R Guide to Durable Concrete4211.1 Recommended Practice for Selecting Proportions forNo
11、rmal, Heavyweight, and Mass Concrete43. Terminology3.1 For definitions of terms used in this test method, refer toTerminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 average chord length ( l ), nthe average length ofthe chords formed by the transection of the voids by the line
12、oftraverse; the unit is a length.3.2.2 paste-air ratio (p/A), nthe ratio of the volume ofhardened cement paste to the volume of the air voids in theconcrete.3.2.3 paste content (p), nthe proportion of the totalvolume of the concrete that is hardened cement paste expressedas percentage by volume.1Thi
13、s test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.65 on Petrography.Current edition approved Oct. 1, 2011. Published November 2011. Originallyapproved in 1960. Last previous edition approved in 2010 as
14、 C457/C457M10a.DOI: 10.1520/C0457_C0457M-11.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
15、lume information, refer to the standards Document Summary page onthe ASTM website.4Available fromAmerican Concrete Institute (ACI), P.O. Box 9094, FarmingtonHills, MI 48333-9094, http:/www.aci-int.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 10
16、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3.1 DiscussionWhen this parameter is calculated, it isthe sum of the proportional volumes of the cement, the netmixing water (including the liquid portions of any chemicaladmixtures), and any supplementary cementit
17、ious materialspresent (7, 8).3.2.4 spacing factor ( L ), na parameter related to themaximum distance in the cement paste from the periphery ofan air void, the unit is a length.3.2.5 specific surface (a), nthe surface area of the airvoids divided by their volume, expressed in compatible unitsso that
18、the unit of specific surface is a reciprocal length.3.2.6 void frequency (n), nvoids per unit length of tra-verse; the number of air voids intercepted by a traverse linedivided by the length of that line; the unit is a reciprocal length.3.2.6.1 DiscussionThe value for void frequency (n) can-not be d
19、irectly determined by the paste-air ratio method as thisvalue refers to the voids per unit measure of traverse in the totalconcrete (including aggregate).3.2.7 water void, na space enclosed by the cement pastethat was occupied by water at the time of setting and frequentlyfound under an aggregate pa
20、rticle or reinforcing bar. A water-void is usually identified by its irregular shape or evidence thata channel or cavity has been created by bleed water trapped inthe concrete at the time it hardened.4. Summary of Test Method4.1 Procedure A, Linear-Traverse MethodThis procedureconsists of the determ
21、ination of the volumetric composition ofthe concrete by summing the distances traversed across a givencomponent along a series of regularly spaced lines in one ormore planes intersecting the sample. The data gathered are thetotal length traversed (Tt), the length traversed through airvoids (Ta), the
22、 length traversed through paste (Tp), and thenumber of air voids intersected by the traverse line (N). Thesedata are used to calculate the air content and various param-eters of the air-void system. If only the air content is desired,only Taand Ttneed be determined.4.2 Procedure B, Modified Point-Co
23、unt MethodThis pro-cedure consists of the determination of the volumetric compo-sition of the concrete by observation of the frequency withwhich areas of a given component coincide with a regular gridsystem of points at which stops are made to enable thedeterminations of composition. These points ma
24、y be in one ormore planes intersecting the sample. The data gathered are thelinear distance between stops along the traverse (I), the totalnumber of stops (St), the number of stops in air voids (Sa), thenumber of stops in paste (Sp), and the number of air voids (N)intersected by the line of traverse
25、 over which the componentdata is gathered. From these data the air content and variousparameters of the air-void system are calculated. If only the aircontent is desired, only Saand Stneed be determined.4.3 Paste-Air Ratio ModificationIn some instances thesample is not representative of the concrete
26、 as a whole, so Ttand Stlose their significance and cannot be used as a basis forcalculations. The most common examples are concrete withlarge coarse aggregate and samples from the finished surfaceregion, for both of which the examined sample consists of adisproportionately large amount of the morta
27、r fraction. In suchinstances the usual procedure must be changed, and thepaste-air ratio modification must be used (see 5.5).5. Significance and Use5.1 The parameters of the air-void system of hardenedconcrete determined by the procedures described in this testmethod are related to the susceptibilit
28、y of the cement pasteportion of the concrete to damage by freezing and thawing.Hence, this test method can be used to develop data to estimatethe likelihood of damage due to cyclic freezing and thawing orto explain why it has occurred. The test method can also beused as an adjunct to the development
29、 of products or proce-dures intended to enhance the resistance of concrete to cyclicfreezing and thawing (1).5.2 Values for parameters of the air-void system can beobtained by either of the procedures described in this testmethod.5.3 No provision is made for distinguishing among en-trapped air voids
30、, entrained air voids, and water voids. Anysuch distinction is arbitrary, because the various types of voidsintergrade in size, shape, and other characteristics. Reports thatdo make such a distinction typically define entrapped air voidsas being larger than 1 mm in at least one dimension beingirregu
31、lar in shape, or both. The honey-combing that is aconsequence of the failure to compact the concrete properly isone type of entrapped air void (9, 10).5.4 Water voids are cavities that were filled with water at thetime of setting of the concrete. They are significant only inmixtures that contained e
32、xcessive mixing water or in whichpronounced bleeding and settlement occurred. They are mostcommon beneath horizontal reinforcing bars, pieces of coarseaggregate and as channelways along their sides. They occuralso immediately below surfaces that were compacted byfinishing operations before the compl
33、etion of bleeding.5.5 Application of the paste-air ratio procedure is necessarywhen the concrete includes large nominal maximum sizeaggregate, such as 50 mm 2 in. or more. Prepared sections ofsuch concrete should include a maximum of the mortarfraction, so as to increase the number of counts on air
34、voids ortraverse across them. The ratio of the volume of aggregate tothe volume of paste in the original mix must be accuratelyknown or estimated to permit the calculation of the air-voidsystems parameters from the microscopically determinedpaste-air ratio.NOTE 1The air-void content determined in ac
35、cordance with this testmethod usually agrees closely with the value determined on the freshconcrete in accordance with Test Methods C138/C138M, C173/C173M,or C231 (11). However, significant differences may be observed if thesample of fresh concrete is consolidated to a different degree than thesampl
36、e later examined microscopically. For concrete with a relatively highair content (usually over 7.5 %), the value determined microscopicallymay be higher by one or more percentage points than that determined byTest Method C231.C457/C457M 112SAMPLING AND SECTION PREPARATION6. Apparatus and Materials f
37、or Sample Preparation (foreither procedure)6.1 Apparatus and materials for the preparation of surfacesof concrete samples for microscopical observation are de-scribed in Practice C856; other apparatus may be equallysuitable.NOTE 2Apparatus for measurement of prepared samples is describedin the two f
38、ollowing procedures.7. Sampling (for either procedure)7.1 Samples of concrete can be obtained from specimenscast in the field or laboratory, or by coring, sawing, orotherwise removing concrete from structures or products. Theprocedure followed and the location from which the samplesare obtained will
39、 depend on the objectives of the program. Ingeneral, secure samples of hardened concrete in accordancewithTest Method C42/C42M or Practice C823 or both. Provideat least the minimum area of finished surface given in Table 1in each sample. A sample may be composed of any number ofspecimens.7.2 For ref
40、eree purposes or to determine the compliance ofhardened concrete with requirements of specifications for theair-void system, obtain samples for analysis by this test methodfrom at least three randomly selected locations over the area orthroughout the body of concrete to be tested, depending uponthe
41、objectives of the investigation.8. Preparation of Sections (for either procedure)8.1 Unless the objectives of the program dictate otherwise,saw the section for observation approximately perpendicular tothe layers in which the concrete was placed or perpendicular tothe finished surface. Individual se
42、ctions should be as large ascan be ground and examined with the available equipment. Therequired area may consist of more than one prepared section.Spread the selected traverse length uniformly over the avail-able surface so as to compensate for the heterogeneity of theconcrete.8.2 If gross irregula
43、rities are present, begin the surfacepreparation by lapping (grinding on a flat surface) withnominal 150 m (No. 100) silicon carbide abrasive. Lap thesurface with successively finer abrasives until it is suitable formicroscopical observation. An appropriate series of abrasiveswould include nominal 7
44、5, 35, 17.5 and 12.5 m grit sizes (No.220, 320, 600, and 800, respectively), and perhaps 5-m (No.2500 grit) aluminum oxide (Note 3). From time to time duringlapping, and when changing to a finer abrasive and whenlapping is complete, clean all surfaces of the specimen gentlyand thoroughly to remove t
45、he grinding compound. Use ofultrasonic cleaners may be harmful to the surface. Suchtreatment should not be used without care and experimentation.Cleaning with a soft cosmetic brush under running water, or bya pressurized dental spray has been successful.Asurface that issatisfactory for microscopical
46、 examination will show an excel-lent reflection of a distant light source when viewed at a lowincident angle and there shall be no noticeable relief betweenthe paste and the aggregate surfaces.Areas that are scratched orimperfect indicate the need for additional preparation; usespecial techniques if
47、 required (see 8.3). The edges of thesections of the air voids will be sharp and not eroded orcrumbled, and air-void sections including those as small as 10m 0.0004 in. in diameter will be clearly distinguishable.(See Fig. 1.) Do not include scratched or broken portions of thesurface in the analyzed
48、 area. If needed to meet the require-ments of Table 1, prepare additional surfaces.NOTE 3Grit numbers of abrasives can denote slightly differentparticle sizes, depending on the manufacturer. The suggested sizes willusually be appropriate, but others may be selected according to theexperience of the
49、user.8.3 Sometimes difficulty will be encountered in preparingthe lapped surfaces. The usual cause is a weak cement-pastematrix. The problem is manifested by the plucking of sandgrains from the surface during the lapping, with consequentscratching of the surface, and by undercutting of the pastearound the harder aggregate particles. Friable particles ofaggregate can also cause difficulty. In such instances thefollowing procedure is helpful. Heat the partially preparedspecimen of concrete to about 150 C 300 F in an oven.(WarningIf the specimen was sawn wit
