1、Designation: C295/C295M 11Standard 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 Department of Defense.1. Scope*1.1 This guide outlines procedures for the petrogra
3、phicexamination 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 selection o
4、f 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 accordance
5、 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 in non
6、-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 and health practices and determine the applica-bility of regulatory limitation
7、s prior to use.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 CoarseAggregatesC294 Descriptive Nomenclature for Constitue
8、nts of Con-crete AggregatesC702 Practice for Reducing Samples of Aggregate to Test-ing SizeD75 Practice for Sampling AggregatesE11 Specification for Woven Wire Test Sieve Cloth and TestSievesE883 Guide for ReflectedLight Photomicrography3. Qualifications of Petrographers3.1 All petrographic examinat
9、ions 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 course workpertaining to basic geology, miner
10、alogy, 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 ofaggregates on the physical and chemical prop
11、erties 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 petrog-rapher should have expertise to properl
12、y 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 a full-timesupervising petrographer who m
13、eets these qualifications. Aresume of the professional experience and education of thepetrographer shall be available.1This 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 a
14、pproved July 1, 2011. Published August 2011. Originallyapproved in 1954. Last previous edition approved in 2008 as C29508. DOI:10.1520/C0295_C0295M-11.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM websit
15、e, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor D
16、rive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 itself, consti-tute sufficient qualification for examination of a
17、ggregates 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 examination will require the use of opticalmicroscopy. Complete pe
18、trographic 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, differential thermal analysis (DTA), infrared spectros-copy, or other sc
19、anning electron microscopy (SEM) energy-dispersive x-ray analysis (EDX). In some instances, suchprocedures are more rapid and more definitive than aremicroscopical methods.4.2 Identification of the constituents of a sample is usually anecessary step towards recognition of the properties that maybe e
20、xpected 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, the com-pleteness and accuracy of the information provided to the
21、petrographer 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 since it is assumed that the guide will beused by persons who a
22、re 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 petrographer will have had experience adequate to providedetailed inter
23、pretation 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 the followingpurposes:5.1.1 To determine the physical and chemica
24、l 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 the relative amounts of the constituentsof the sample that are es
25、sential 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 samples of aggregate from one or more sources, for whichtest dat
26、a 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 objectives of the examination, thekind of information needed, and
27、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 may form the basis for establishing arrange-ments between a pur
28、chaser 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 agreement in writing. The agreement maystipulate specific determ
29、inations 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-tion of aggregate, but petrographic examination is also used forma
30、ny 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 required.5.5 The petrographic examination should establish wheth
31、erthe 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 such assmectites (formerly known as the montmorillonite-saponite
32、group 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 1063 F,with accompanying volume increase.5.6 Petrographic examinat
33、ion 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 proportion of each rock type in each condition.If the concrete in whi
34、ch 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 damage by freezing and thawing and willcause the aggregate portion
35、 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 to form popouts, which are blemishes onpavements and walls.5.7 P
36、etrographic examinations may also be used to deter-mine the proportions of cubic, spherical, ellipsoidal, pyramidal,tabular, flat, and elongated particles in an aggregate sample orsamples. Flat, elongated, and thin chip-like particles in aggre-gate increase the mixing water requirement and hence dec
37、reaseconcrete strength.C295/C295M 1125.8 Petrographic examination should identify and call atten-tion to potentially alkali-silica reactive and alkali-carbonatereactive constituents, determine such constituents quantita-tively, and recommend additional tests to confirm or refute thepresence in signi
38、ficant amounts of aggregate constituentscapable of alkali reaction in concrete. See Specification C33.Alkali-silica reactive constituents found in aggregates include:opal, chalcedony, cristobalite, tridymite, highly strained quartz,microcrystalline quartz, volcanic glass, and synthetic siliceousglas
39、s. Aggregate materials containing these constituents in-clude: glassy to cryptocrystalline intermediate to acidic volca-nic rocks, some argillites, phyllites, graywacke, gneiss, schist,gneissic granite, vein quartz, quartzite, sandstone, and chert.Criteria are available for identifying the minerals
40、in the listabove by their optical properties or by XRD (2),(3). Criteria areavailable for identifying rocks by their mineral compositionand texture (4). Examination in both reflected and transmittedlight may be necessary to provide data for these identifications.X-ray microanalysis using energy-disp
41、ersive x-ray spectrom-eters with scanning electron microscopy (SEM/EDX) orwavelength-dispersive x-ray spectrometers in electron micro-probes (EMPA/WDX) may provide useful information on thechemical composition of minerals and rocks. Potentially del-eterious alkali-carbonate reactive rocks are usuall
42、y calcareousdolomites or dolomitic limestones with clayey insoluble resi-dues. Some dolomites essentially free of clay and some veryfine-grained limestones free of clay and with minor insolubleresidue, mostly quartz, are also capable of some alkali-carbonate reactions, however, such reactions are no
43、t necessar-ily deleterious.5.9 Petrographic examination may be directed specificallyat the possible presence of contaminants in aggregates, such assynthetic glass, cinders, clinker, or coal ash, magnesium oxide,calcium oxide, or both, gypsum, soil, hydrocarbons, chemicalsthat may affect the setting
44、behavior of concrete or the proper-ties of the aggregate, animal excrement, plants or rottenvegetation, and any other contaminant that may prove unde-sirable in concrete.5.10 These objectives, for which this guide was prepared,will have been attained if those involved with the evaluation ofaggregate
45、 materials for use in concrete construction havereasonable assurance that the petrographic examination resultswherever and whenever obtained may confidently be com-pared.6. Apparatus and Supplies6.1 The apparatus and supplies listed as follows comprise aselection that will permit the use of the proc
46、edures described inthis guide. All specific items listed have been used, in connec-tion with the performance of petrographic examinations, by theprocedures described herein; it is not, however, intended toimply that other items cannot be substituted to serve similarfunctions. Whenever possible the s
47、election 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 mak
48、ing of petrographicexaminations of aggregate samples are those items, or equiva-lent apparatus or supplies that will serve the same purpose, thatare indicated by asterisks in the lists given as follows.6.1.1 Apparatus and Supplies for Preparation of Specimens:6.1.1.1 Rock-Cutting Saw, * preferably w
49、ith 350-mm 14-in. diameter or larger diamond blade, and automatic feed.6.1.1.2 Horizontal Grinding Wheel, * preferably 400-mm16-in. diameter.6.1.1.3 Polishing Wheel, preferably 200- to 300-mm 8 to12-in. diameter.6.1.1.4 Abrasives* , Silicon carbide grit No. 100 122 m,220 63 m, 320 31 m, 600 16 m, and 800 12 m;alumina M-305 5 m.46.1.1.5 Geologists Pick or Hammer.6.1.1.6 Microscope Slides*, clear, noncorrosive, 25 by 45mm 1 by 2 in. in size.6.1.1.7 Mounting Medium for Powder Mounts* Canadabalsam, neutral, in xylene; suitable low-viscosity epoxy resi
