1、Designation: C295/C295M 18Standard Guide forPetrographic Examination of Aggregates for Concrete1This standard is issued under the fixed designation C295/C295M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval.A superscript 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 guide outlines procedures for the pet
3、rographicexamination of samples representative of materials proposedfor use as aggregates in cementitious mixtures or as rawmaterials for use in production of such aggregates. This guideis based on Ref (1).21.2 This guide outlines the extent to which petrographictechniques should be used, the select
4、ion of properties thatshould be looked for, and the manner in which such techniquesmay be employed in the examination of samples of aggregatesfor concrete.1.3 The rock and mineral names given in DescriptiveNomenclature C294 should be used, insofar as they areappropriate, in reports prepared in accor
5、dance with this guide.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 independently of the other. Combiningvalues from the two systems may result i
6、n non-conformancewith the standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of
7、regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Tra
8、de Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3C33 Specification for Concrete AggregatesC117 Test Method for Materials Finer than 75-m (No. 200)Sieve in Mineral Aggregates by WashingC136 Test Method for Sieve Analysis of Fine and CoarseAggregate
9、sC294 Descriptive Nomenclature for Constituents of Con-crete AggregatesC702 Practice for Reducing Samples ofAggregate to TestingSizeD75 Practice for Sampling AggregatesE11 Specification for Woven Wire Test Sieve Cloth and TestSievesE883 Guide for ReflectedLight Photomicrography3. Qualifications of P
10、etrographers3.1 All petrographic examinations of aggregate for use inconcrete as described in this guide should be performed by apetrographer with at least 5 years experience in petrographicexamination of concrete or concrete-making materials. Thepetrographer should have completed college-level cour
11、se workpertaining to basic geology, mineralogy, petrography, andoptical mineralogy or have obtained equivalent knowledgethrough experience and on-the-job training. Completion ofcourse work in concrete materials is also advantageous. Thepetrographer should have experience evaluating the effects ofagg
12、regates on the physical and chemical properties of hardenedconcrete. Identification of individual minerals in aggregateparticles, classification of rock types, and categorizing thephysical and chemical properties of rocks and minerals shouldalso be included in the petrographers experience. The petro
13、g-rapher should have expertise to properly use the equipment andapparatus described in Section 6 and provide detailed interpre-tations of the petrographic examination. If the petrographerdoes not meet these qualifications, the individual may performsuch examinations under the technical direction of
14、a full-time1This guide is under the jurisdiction of ASTM Committee C09 on Concrete andConcrete Aggregates and is the direct responsibility of Subcommittee C09.65 onPetrography.Current edition approved July 1, 2018. Published September 2018. Originallyapproved in 1954. Last previous edition approved
15、in 2012 as C295/C295M 12.DOI: 10.1520/C0295_C0295M-18.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStand
16、ards volume information, refer to the standards Document Summary page onthe ASTM website.*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 StatesThis international standard was d
17、eveloped in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1supervising pet
18、rographer who meets these qualifications. Aresume of the professional experience and education of thepetrographer shall be available.3.1.1 Licensing, certification, or other accreditation by agovernmental agency or other organization stating the indi-vidual is a professional geologist should not, by
19、 itself, consti-tute sufficient qualification for examination of aggregates forconcrete.4. Summary of Method4.1 The specific procedures employed in the petrographicexamination of any sample will depend to a large extent on thepurpose of the examination and the nature of the sample. Inmost cases the
20、examination will require the use of opticalmicroscopy. Complete petrographic examinations for particu-lar purposes and to investigate particular problems may requireexamination of aggregates or of selected constituents by meansof additional procedures, such as X-ray diffraction (XRD)analysis, differ
21、ential thermal analysis (DTA), infraredspectroscopy, or other scanning electron microscopy (SEM)energy-dispersive x-ray analysis (EDX). In some instances,such procedures are more rapid and more definitive than aremicroscopical methods.4.2 Identification of the constituents of a sample is usually ane
22、cessary step towards recognition of the properties that maybe expected to influence the behavior of the material in itsintended use, but identification is not an end in itself. The valueof any petrographic examination will depend to a large extenton the representativeness of the samples examined, th
23、e com-pleteness and accuracy of the information provided to thepetrographer concerning the source and proposed use of thematerial, and the petrographers ability to correlate these datawith the findings of the examination.4.3 This guide does not attempt to describe the techniquesof petrographic work
24、since it is assumed that the guide will beused by persons who are qualified by education and experienceto employ such techniques for the recognition of the charac-teristic properties of rocks and minerals and to describe andclassify the constituents of an aggregate sample. In some cases,the petrogra
25、pher will have had experience adequate to providedetailed interpretation of the results. In others, the interpreta-tion will be made in part by engineers or others qualified torelate the observations to the questions to be answered.5. Significance and Use5.1 Petrographic examinations are made for th
26、e followingpurposes:5.1.1 To determine the physical and chemical characteristicsof the material that may be observed by petrographic methodsand that have a bearing on the performance of the material inits intended use.5.1.2 To describe and classify the constituents of thesample,5.1.3 To determine th
27、e relative amounts of the constituentsof the sample that are essential for proper evaluation of thesample when the constituents differ significantly in propertiesthat have a bearing on the performance of the material in itsintended use, and5.1.4 To compare samples of aggregate from new sourceswith s
28、amples of aggregate from one or more sources, for whichtest data or performance records are available.5.2 This guide may be used by a petrographer employeddirectly by those for whom the examination is made. Theemployer should tell the petrographer, in as much detail asnecessary, the purposes and obj
29、ectives of the examination, thekind of information needed, and the extent of examinationdesired. Pertinent background information, including results ofprior testing, should be made available. The petrographersadvice and judgment should be sought regarding the extent ofthe examination.5.3 This guide
30、may form the basis for establishing arrange-ments between a purchaser of consulting petrographic serviceand the petrographer. In such a case, the purchaser and theconsultant should together determine the kind, extent, andobjectives of the examination and analyses to be made, andshould record their a
31、greement in writing. The agreement maystipulate specific determinations to be made, observations to bereported, funds to be obligated, or a combination of these orother conditions.5.4 Petrographic examination of aggregate considered foruse in hydraulic-cement concrete is one aspect of the evalua-tio
32、n of aggregate, but petrographic examination is also used formany other purposes. Petrographic examinations provide iden-tification of types and varieties of rocks present in potentialaggregates. However, as noted above, identification of everyrock and mineral present in an aggregate source is not r
33、equired.5.5 The petrographic examination should establish whetherthe aggregate contains chemically unstable minerals such assoluble sulfates, unstable sulfides that may form sulfuric acidor create distress in concrete exposed to high temperaturesduring service, or volumetrically unstable materials s
34、uch assmectites (formerly known as the montmorillonite-saponitegroup of minerals or swelling clays). Specifications may limitthe quartz content of aggregates for use in concrete that may besubject to high temperature (purposefully or accidentally)because of the conversion to beta-quartz at 573 C 106
35、3 F,with accompanying volume increase.5.6 Petrographic examination should identify the portion ofeach coarse aggregate that is composed of weathered orotherwise altered particles and the extent of that weathering oralteration, whether it is severe, moderate, or slight, and shoulddetermine the propor
36、tion of each rock type in each condition.If the concrete in which the aggregate may be used will beexposed to freezing and thawing in a critically saturatedcondition, finely porous and highly weathered or otherwisealtered rocks should be identified because they will be espe-cially susceptible to dam
37、age by freezing and thawing and willcause the aggregate portion of the concrete to fail in freezingand thawing. This will ultimately destroy the concrete becausesuch aggregates cannot be protected by adequately air-entrained mortar. Finely porous aggregates near the concretesurface are also likely t
38、o form popouts, which are blemishes onpavements and walls.5.7 Petrographic examinations may also be used to deter-mine the proportions of cubic, spherical, ellipsoidal, pyramidal,C295/C295M 182tabular, flat, and elongated particles in an aggregate sample orsamples. Flat, elongated, and thin chip-lik
39、e particles in aggre-gate increase the mixing water requirement and hence decreaseconcrete strength.5.8 Petrographic examination should identify and call atten-tion to potentially alkali-silica reactive and alkali-carbonatereactive constituents, determine such constituentsquantitatively, and recomme
40、nd additional tests to confirm orrefute the presence in significant amounts of aggregate con-stituents capable of alkali reaction in concrete. See Specifica-tion C33. Alkali-silica reactive constituents found in aggre-gates include: opal, chalcedony, cristobalite, tridymite, highlystrained quartz, m
41、icrocrystalline quartz, cryptocrystallinequartz, volcanic glass, and synthetic siliceous glass. Aggregatematerials containing these constituents include: glassy tocryptocrystalline intermediate to acidic volcanic rocks, someargillites, phyllites, graywacke, gneiss, schist, gneissic granite,vein quar
42、tz, quartzite, sandstone, chert, and carbonate rockscontaining alkali reactive forms of silica. Criteria are availablefor identifying the minerals in the list above by their opticalproperties or by XRD (2),(3). Criteria are available for identi-fying rocks by their mineral composition and texture (4
43、).Examination in both reflected and transmitted light may benecessary to provide data for these identifications. X-raymicroanalysis using energy-dispersive x-ray spectrometerswith scanning electron microscopy (SEM/EDX) orwavelength-dispersive x-ray spectrometers in electron micro-probes (EMPA/WDX) m
44、ay provide useful information on thechemical composition of minerals and rocks. Potentially del-eterious alkali-carbonate reactive rocks are usually calcareousdolomites or dolomitic limestones with clayey insoluble resi-dues. Some dolomites essentially free of clay and some veryfine-grained limeston
45、es free of clay and with minor insolubleresidue, mostly quartz, are also capable of some alkali-carbonate reactions, however, such reactions are not necessar-ily deleterious.5.9 Petrographic examination may be directed specificallyat the possible presence of contaminants in aggregates, such assynthe
46、tic glass, cinders, clinker, or coal ash, magnesium oxide,calcium oxide, or both, gypsum, soil, hydrocarbons, chemicalsthat may affect the setting behavior of concrete or the proper-ties of the aggregate, animal excrement, plants or rottenvegetation, and any other contaminant that may prove unde-sir
47、able in concrete.5.10 These objectives, for which this guide was prepared,will have been attained if those involved with the evaluation ofaggregate materials for use in concrete construction havereasonable assurance that the petrographic examination resultswherever and whenever obtained may confiden
48、tly be com-pared.6. Apparatus and Supplies6.1 The apparatus and supplies listed as follows comprise aselection that will permit the use of the procedures described inthis guide. All specific items listed have been used, in connec-tion with the performance of petrographic examinations, by theprocedur
49、es described herein; it is not, however, intended toimply that other items cannot be substituted to serve similarfunctions. Whenever possible the selection of particular appa-ratus and supplies should be left to the judgment of thepetrographer who is to perform the work so that the itemsobtained will be those with the use of which the petrographerhas the greatest experience and familiarity. The minimumequipment regarded as essential to the making of petrographicexaminations of aggregate samples are those items, or equiva-lent apparatus or supplies that will serve the same p
