1、Designation: C457/C457M 11 C457/C457M 12Standard 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 t
3、he air content of hardened concrete and of thespecific surface, void frequency, spacing factor, and paste-air ratio of the air-void system in hardened concrete (1).2 Two proceduresare described:1.1.1 Procedure A, the linear-traverse method (2, 3).1.1.2 Procedure B, the modified point-count method (3
4、, 4, 5, 6).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 outline the principles of this test method and to establish standards for its adequate performance but notto desc
5、ribe 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 separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system
6、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 concerns associated with its use. It is the responsibility of theuser of this standard to establish appropria
7、te safety and health practices and determine the applicability of regulatory limitationsprior to use. For specific hazard statements see 8.3 and 10.1.2. Referenced Documents2.1 ASTM Standards:3C42/C42M Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of ConcreteC125 Terminology Re
8、lating to Concrete and Concrete AggregatesC138/C138M Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of ConcreteC173/C173M Test Method for Air Content of Freshly Mixed Concrete by the Volumetric MethodC231 Test Method for Air Content of Freshly Mixed Concrete by the Press
9、ure MethodC666/C666M Test Method for Resistance of Concrete to Rapid Freezing and ThawingC670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction MaterialsC672/C672M Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing ChemicalsC823 Practice f
10、or Examination and Sampling of Hardened Concrete in ConstructionsC856 Practice for Petrographic Examination of Hardened ConcreteD92 Test Method for Flash and Fire Points by Cleveland Open Cup Tester2.2 American Concrete Institute Standards:201.2R Guide to Durable Concrete4211.1 Recommended Practice
11、for Selecting Proportions for Normal, Heavyweight, and Mass Concrete41 This test method is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregatesand is the direct responsibility of Subcommittee C09.65 onPetrography.Current edition approved Oct. 1, 2011Dec. 1, 2012. Publishe
12、d November 2011December 2012. Originally approved in 1960. Last previous edition approved in 20102011as C457/C457M10a.11. DOI: 10.1520/C0457_C0457M-11.10.1520/C0457_C0457M-12.2 The boldface numbers in parentheses refer to the list of references at the end of this test method.3 For referenced ASTM st
13、andards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4 Available from American Concrete Institute (ACI), P.O. Box 9094, Farmington Hill
14、s, MI 48333-9094, http:/www.aci-int.org.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 technically possible to adequately depict all changes accurately, ASTM
15、 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 standardCopyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959. United States13. 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 length l!, nthe average length of the chords formed by the transection of the
17、 voids by the line of traverse;the unit is a length.3.2.2 paste-air ratio (p/A),nthe ratio of the volume of hardened cement paste to the volume of the air voids in the concrete.3.2.3 paste content (p), nthe proportion of the total volume of the concrete that is hardened cement paste expressed asperc
18、entage by volume.3.2.3.1 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 present (7, 8).3.2.4 spacing factor L!, na param
19、eter related to the maximum distance in the cement paste from the periphery of an air void,the unit is a length.3.2.5 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.3.2.6 void f
20、requency (n), nvoids per unit length of traverse; the number of air voids intercepted by a traverse line divided bythe length of that line; the unit is a reciprocal length.3.2.6.1 DiscussionThe value for void frequency (n) cannot be directly determined by the paste-air ratio method as this value ref
21、ers to the voids perunit measure of traverse in the total concrete (including aggregate).3.2.7 water void, na space enclosed by the cement paste that was occupied by water at the time of setting and frequently foundunder an aggregate particle or reinforcing bar. A water-void is usually identified by
22、 its irregular shape or evidence that a channelor 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 determination of the volumetric composition of theconcrete by summin
23、g the distances traversed across a given component along a series of regularly spaced lines in one or moreplanes intersecting the sample. The data gathered are the total length traversed (Tt), the length traversed through air voids (Ta ),the length traversed through paste (Tp), and the number of air
24、 voids intersected by the traverse line (N). These data are used tocalculate the air content and various parameters of the air-void system. If only the air content is desired, only Ta and Tt need bedetermined.4.2 Procedure B, Modified Point-Count MethodThis procedure consists of the determination of
25、 the volumetric compositionof the concrete by observation of the frequency with which areas of 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. The dat
26、a gathered are the linear distance between stops along the traverse (I), the total number of stops (St), the numberof stops in air voids (Sa), the number of stops in paste (Sp), and the number of air voids (N) intersected by the line of traverse overwhich the component data is gathered. From these d
27、ata the air content and various parameters of the air-void system are calculated.If only the air content is desired, only Sa and St need be determined.4.3 Paste-Air Ratio ModificationIn some instances the sample is not representative of the concrete as a whole, so Tt and Stlose their significance an
28、d cannot be used as a basis for calculations. The most common examples are concrete with large coarseaggregate and samples from the finished surface region, for both of which the examined sample consists of a disproportionatelylarge amount of the mortar fraction. In such instances the usual procedur
29、e must be changed, and the paste-air ratio modificationmust 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 portion of the concrete
30、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 procedures intended to enha
31、nce theresistance of concrete to cyclic freezing and thawing (1).5.2 Values for parameters of the air-void system can be obtained by either of the procedures described in this test method.C457/C457M 1225.3 No provision is made for distinguishing among entrapped air voids, entrained air voids, and wa
32、ter 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 than 1 mm in at least one dimension being irregular in shape,or both. The
33、honey-combing that is a consequence of the failure to compact the concrete properly is one type of entrapped air void(9, 10).5.4 Water voids are cavities that were filled with water at the time of setting of the concrete. They are significant only inmixtures that contained excessive mixing water or
34、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 that were compacted by finishing operations before the completion of bleeding.5.5
35、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 mortar fraction, so as toincrease the number of counts on air voids or traverse ac
36、ross 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 determined paste-air ratio.NOTE 1The air-void content determined in accordance with thi
37、s test method usually agrees closely with the value determined on the fresh concretein accordance with Test Methods C138/C138M, C173/C173M, or C231 (11). However, significant differences may be observed if the sample of freshconcrete is consolidated to a different degree than the sample later examin
38、ed microscopically. For concrete with a relatively high air content (usually over7.5 %), the value determined microscopically may be higher by one or more percentage points than that determined by Test Method C231.SAMPLING AND SECTION PREPARATION6. Apparatus and Materials for Sample Preparation (for
39、 either procedure)6.1 Apparatus and materials for the preparation of surfaces of concrete samples for microscopical observation are described inPractice C856; other apparatus may be equally suitable.NOTE 2Apparatus for measurement of prepared samples is described in the two following procedures.7. S
40、ampling (for either procedure)7.1 Samples of concrete can be obtained from specimens cast in the field or laboratory, or by coring, sawing, or otherwiseremoving concrete from structures or products. The procedure followed and the location from which the samples are obtained willdepend on the objecti
41、ves of the program. In general, secure samples of hardened concrete in accordance with Test MethodC42/C42M or Practice C823 or both. Provide at least the minimum area of finished surface given in Table 1 in each sample. Asample may be composed of any number of specimens.7.2 For referee purposes or t
42、o determine the compliance of hardened concrete with requirements of specifications for theair-void system, obtain samples for analysis by this test method from at least three randomly selected locations over the area orthroughout the body of concrete to be tested, depending upon the objectives of t
43、he investigation.TABLE 1 Minimum Area of Finished Surface for MicroscopicalMeasurementANominal or ObservedMaximum Size of Aggregatein the Concrete, mm in.Total Area to be Traversed forDetermination of A, or LB , min, cm2in.2Based on Direct Measurement of:Total Air-VoidContent Paste-Air Ratio, p/A150
44、 6 1613 250 645 10075 3 419 65 194 3037.5 112 155 24 97 1525.0 1 77 12 77 1219.0 34 71 11 71 1112.5 12 65 10 65 109.5 38 58 9 58 94.75 (No. 4) 45 7 45 7A The indicated values refer to reasonably homogeneous, well-compacted con-crete. The microscopical measurement should be made on proportionately la
45、rgerarea of sections if the concrete is markedly heterogeneous in distribution ofaggregate or large air voids. If more than one finished surface is taken from asingle portion of the concrete, the finished surfaces shall be separated by adistance greater than one half of the nominal or observed maxim
46、um size ofaggregate.B See Section 3 for the interpretation of symbols employed.C457/C457M 1238. Preparation of Sections (for either procedure)8.1 Unless the objectives of the program dictate otherwise, saw the section for observation approximately perpendicular to thelayers in which the concrete was
47、 placed or perpendicular to the finished surface. Individual sections should be as large as can beground and examined with the available equipment. The required area may consist of more than one prepared section. Spread theselected traverse length uniformly over the available surface so as to compen
48、sate for the heterogeneity of the concrete.8.2 If gross irregularities are present, begin the surface preparation by lapping (grinding on a flat surface) with nominal 150 m(No. 100) silicon carbide abrasive. Lap the surface with successively finer abrasives until it is suitable for microscopicalobse
49、rvation. An appropriate series of abrasives would include nominal 75, 35, 17.5 and 12.5 m grit sizes (No. 220, 320, 600, and800, respectively), and perhaps 5-m (No. 2500 grit) aluminum oxide (Note 3). From time to time during lapping, and whenchanging to a finer abrasive and when lapping is complete, clean all surfaces of the specimen gently and thoroughly to removethe grinding compound. Use of ultrasonic cleaners may be harmful to the surface. Such treatment should not be used without careand
