1、Designation: C457/C457M 12C457/C457M 16Standard 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
2、or, in the case 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 microscopical determinations of th
3、e air content of hardened concrete and of thespecific surface, void frequency, spacing factor, and paste-air ratio of the air-void system in hardened concreteconcrete. (Three1).Two procedures are described:1.1.1 Procedure A, A the linear-traverse method Linear-traverse method. (2, 3).1.1.2 Procedure
4、 B, B the modified point-count methodModified point-count method. (3, 4, 5, 6).1.1.3 Procedure CContrast enhanced method.1.2 This test method is based on prescribed procedures that are applied to sawed and lapped sections of specimens of concretefrom the field or laboratory.1.3 It is intended to out
5、line the principles of this test method and to establish standards for its adequate performance but notto describe in detail all the possible variations that might be used to accomplish the objectives of this test method.1.4 The values stated in either SI units or inch-pound units are to be regarded
6、 separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.5 This standard does not purport to address all of the safety
7、 concerns associated with its use. It is the responsibility of theuser of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitationsprior to use. For specific hazard statements see 8.3Note 9 and 10.1Note 12.1.6 This international stan
8、dard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Refe
9、renced Documents2.1 ASTM Standards:2C42/C42M Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of ConcreteC125 Terminology Relating to Concrete and Concrete AggregatesC138/C138M Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of ConcreteC173/C173M Test M
10、ethod for Air Content of Freshly Mixed Concrete by the Volumetric MethodC231C231/C231M Test Method for Air Content of Freshly Mixed Concrete by the Pressure MethodC666/C666M Test Method for Resistance of Concrete to Rapid Freezing and ThawingC670 Practice for Preparing Precision and Bias Statements
11、for Test Methods for Construction MaterialsC672/C672M Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing ChemicalsC823C823/C823M Practice for Examination and Sampling of Hardened Concrete in ConstructionsC856 Practice for Petrographic Examination of Hardened ConcreteD92 Test
12、Method for Flash and Fire Points by Cleveland Open Cup Tester1 This test method is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.65 onPetrography.Current edition approved Dec. 1, 2012Dec. 1, 2016. Published Decem
13、ber 2012April 2017. Originally approved in 1960. Last previous edition approved in 20112012 asC457/C457M 11.12. DOI: 10.1520/C0457_C0457M-12.10.1520/C0457_C0457M-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Boo
14、k of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This 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 techni
15、cally 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 considered the official document.*A Summary of Changes section appears at the end of this s
16、tandardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.2 American Concrete Institute Standards:3201.2R Guide to Durable Concrete211.1 RecommendedStandard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete3
17、. Terminology3.1 For definitions of terms used in this test method, refer to Terminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 average chord lengthl!, nthe average length of the chords formed by the transection of the voids by the line of traverse;the unit is a length.3.2.2 b
18、inary image, nformed by segmenting an image using only one threshold with the resulting image having only areasof black or white.3.2.3 digital image, nan image captured using a computer-based storage method where the information presented in the imagecan be seen visually, like a traditional photogra
19、phic image, but can also be extracted in a numeric form that can be used foradditional analysis.3.2.4 paste-air ratio (p/A),nthe ratio of the volume of hardened cement paste to the volume of the air voids in the concrete.3.2.5 paste content (p), nthe proportion of the total volume of the concrete th
20、at is hardened cement paste expressed aspercentage by volume.3.2.5.1 DiscussionWhen this parameter is calculated, it is the sum of the proportional volumes of the cement, the net mixing water (including theliquid portions of any chemical admixtures), and any supplementary cementitious materials pres
21、ent present.(7, 8).3.2.6 pixel, nthe smallest definable point of a digital image that has an assigned value representing the brightness of thatcomponent in an image.3.2.6.1 DiscussionTypically a pixel will have the same aspect ratio as the overall image and will have an assigned integer value occurr
22、ing in the range0-255. Multiple pixels are arranged contiguously in two-dimensional arrays to form a digital image.3.2.7 segment, vthe process of placing image pixels into classes or like-groupings using any number of thresholds.3.2.8 spacing factor L!, na parameter related to the maximum distance i
23、n the cement paste from the periphery of an air void,the unit is a length.3.2.9 specific surface (), nthe surface area of the air voids divided by their volume, expressed in compatible units so that theunit of specific surface is a reciprocal length.3.2.10 threshold, na value used to discriminate pi
24、xels into more than one class or like grouping.3.2.11 void frequency (n), nvoids per unit length of traverse; the number of air voids intercepted by a traverse line dividedby the length of that line; the unit is a reciprocal length.3.2.11.1 DiscussionThe value for void frequency (n) cannot be direct
25、ly determined by the paste-air ratio method as this value refers to the voids perunit measure of traverse in the total concrete (including aggregate).3.2.12 water void, na space enclosed by the cement paste that was occupied by water at the time of setting and frequentlyfound under an aggregate part
26、icle or reinforcing bar. A water-void is usually identified by its irregular shape or evidence that achannel or cavity has been created by bleed water trapped in the concrete at the time it hardened.4. Summary of Test Method4.1 Procedure A, Linear-Traverse MethodThis procedure consists of the determ
27、ination of the volumetric composition of theconcrete by summing the distances traversed across a given component along a series of regularly spaced lines in one or moreplanes intersecting the sample.specimen. The data gathered are the total length traversed (Tt), the length traversed through air voi
28、ds3 Available from American Concrete Institute (ACI), P.O. Box 9094, Farmington Hills, MI 48333-9094, http:/www.aci-int.org.C457/C457M 162(Ta), the length traversed through paste (Tp), and the number of air voids intersected by the traverse line (N). These data are usedto calculate the air content a
29、nd various parameters of the air-void system. If only the air content is desired, only Ta and Tt needbe determined.4.2 Procedure B, Modified Point-Count MethodThis procedure consists of the determination of the volumetric compositionof the concrete by observation of the frequency with which areas of
30、 a given component coincide with a regular grid system ofpoints at which stops are made to enable the determinations of composition. These points may be in one or more planes intersectingthe sample.specimen. The data gathered are the linear distance between stops along the traverse (I), the total nu
31、mber of stops (St),the number of stops in air voids (Sa), the number of stops in paste (Sp), and the number of air voids (N) intersected by the line oftraverse over which the component data is gathered. From these data the air content and various parameters of the air-void systemare calculated. If o
32、nly the air content is desired, only Sa and St need be determined.4.3 Procedure C, Contrast Enhanced MethodThis procedure consists of the determination of the volumetric composition ofthe concrete by summing distances measured in digital images of a prepared concrete surface using a series of regula
33、rly spacedlines in one or more digital images obtained from one or more planes intersecting the specimen. The specimen is prepared exactlyas described for Procedures A and B with the additional steps of darkening the specimen surface and filling the air voids with afine particle size white powder. T
34、he data gathered are the total length measured (Tt), the length measured through air voids (Ta),and the number of air voids intersected by the measurement lines (N). These data are used to calculate the air content and variousparameters of the air-void system, except the paste-air ratio and spacing
35、factor that require determination of the paste content (Tp)as described in 16.1. If only the air content is desired, only Ta and Tt need be determined.4.4 Paste-Air Ratio ModificationIn some instances the samplespecimen is not representative of the concrete as a whole, soTt and St lose their signifi
36、cance and cannot be used as a basis for calculations. The most common examples are concrete with largecoarse aggregate and samplesspecimens from the finished surface region, for both of which the examined samplespecimen consistsof a disproportionately large amount of the mortar fraction. In such ins
37、tances 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 hardened concrete determined by the procedures described in this test method arerelated to the susceptibility of the cement paste
38、 portion of the concrete to damage by freezing and thawing. Hence, this test methodcan be used to develop data to estimate the likelihood of damage due to cyclic freezing and thawing or to explain why it hasoccurred. The test method can also be used as an adjunct to the development of products or pr
39、ocedures intended to enhance theresistance of concrete to cyclic freezing and thawingthawing. (1).5.2 Values for parameters of the air-void system can be obtained by eitherany of the procedures described in this test method.The selection of which one of the three methods to be used shall be subject
40、to agreement of the user and provider of thedeterminationNOTE 1Because Procedure C requires darkening the paste and aggregate, its use must occur after other tests if the analyst is also gatheringpetrographic data in addition to the measurements described in this test method.5.3 No provision is made
41、 for distinguishing among entrapped air voids, entrained air voids, and water voids. Any suchdistinction is arbitrary, because the various types of voids intergrade in size, shape, and other characteristics. Reports that do makesuch a distinction typically define entrapped air voids as being larger
42、than 1 mm in at least one dimension being irregular in shape,or both. The honey-combing that is a consequence of the failure to compact the concrete properly is one type of entrapped air voidvoid.(9, 10).5.4 Water voids are cavities that were filled with water at the time of setting of the concrete.
43、 They are significant only inmixtures that contained excessive mixing water or in which pronounced bleeding and settlement occurred. They are most commonbeneath horizontal reinforcing bars, pieces of coarse aggregate and as channelways along their sides. They occur also immediatelybelow surfaces tha
44、t were compacted by finishing operations before the completion of bleeding.5.5 Application of the paste-air ratio procedure is necessary when the concrete includes large nominal maximum size aggregate,such as 50 mm 2 in. or more. Prepared sections of such concrete should include a maximum of the mor
45、tar fraction, so as toincrease the number of counts on air voids or traverse across them. The ratio of the volume of aggregate to the volume of pastein the original mix must be accurately known or estimated to permit the calculation of the air-void systems parameters from themicroscopically determin
46、ed paste-air ratio.NOTE 2The air-void content determined in accordance with this test method usually agrees closely with the value determined on the fresh concretein accordance with Test Methods C138/C138M, C173/C173M, or C231C231/C231M (. 11).However, significant differences may be observed if thes
47、ample of fresh concrete is consolidated to a different degree than the samplespecimen later examined microscopically. For concrete with a relatively highair content (usually over 7.5 %), the value determined microscopically may be higher by one or more percentage points than that determined by TestM
48、ethod C231C231/C231M.C457/C457M 163SAMPLING AND SECTION PREPARATION6. Apparatus and Materials for Sample Preparation (for either procedure) Specimen Preparation6.1 Apparatus and materials for the preparation of surfaces of concrete samples for microscopical observation are described inPractice C856;
49、 other apparatus may be equally suitable. Apparatus and Materials for All ProceduresNOTE 2Apparatus for measurement of prepared samples is described in the two following procedures.6.1.1 Apparatus and materials for the preparation of surfaces of concrete speciemens for microscopical observation aredescribed in Practice C856; other apparatus may be equally suitable.6.2 Materials for Procedure C6.2.1 Opaque Permanent Black Ink, wide felt-tipped marker, black ink stamp pad, or black ink roller, or similar.6.2.2 White Powder, barium sulfate, wollas
