1、Designation: C 295 08Standard Guide forPetrographic Examination of Aggregates for Concrete1This standard is issued under the fixed designation C 295; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er in parentheses indicates the year of last reapproval. Asuperscript 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 petrographicexamin
3、ation 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 of properti
4、es 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 C 294 should be used, insofar as they areappropriate, in reports prepared in accordance with thi
5、s guide.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion purposes only and are not considered standard.1.5 This standard does not purport to address all of thesafety
6、 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 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C33 Specification for Concrete Agg
7、regatesC117 Test Method for Materials Finer than 75-m (No.200) Sieve in Mineral Aggregates by WashingC 136 Test Method for Sieve Analysis of Fine and CoarseAggregatesC 294 Descriptive Nomenclature for Constituents of Con-crete AggregatesC 702 Practice for Reducing Samples of Aggregate toTesting Size
8、D75 Practice for Sampling AggregatesE11 Specification for Wire Cloth and Sieves for TestingPurposesE 883 Guide for ReflectedLight Photomicrography3. Qualifications of Petrographers3.1 All petrographic examinations of aggregate for use inconcrete as described in this guide should be performed by apet
9、rographer 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, mineralogy, petrography, andoptical mineralogy or have obtained equivalent knowledgethrough expe
10、rience 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 properties of hardenedconcrete. Identification of individual minerals in aggregateparticles, cl
11、assification 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 properly use the equipment andapparatus described in Section 6 and provide detailed interpre-tatio
12、ns 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 meets these qualifications. Aresume of the professional experience and education of thepetro
13、grapher 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 itself, consti-tute sufficient qualification for examination of aggregates forconcrete.1This guide is und
14、er 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, 2008. Published December 2008. Originallyapproved in 1954. Last previous edition approved in 2003 as C 295 03.2The boldf
15、ace 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 ASTMStandards volume information, refer to the standards Document Summary
16、 page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Method4.1 The specific procedures employed in the petrographicexamination of any
17、 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 petrographic examinations for particu-lar purposes and to investigate particular problems may requireexamination of ag
18、gregates or of selected constituents by meansof additional procedures, such as X-ray diffraction (XRD)analysis, differential thermal analysis (DTA), infrared spectros-copy, or other scanning electron microscopy (SEM) energy-dispersive x-ray analysis (EDX). In some instances, suchprocedures are more
19、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 expected to influence the behavior of the material in itsintended use, but identification is not an end in itself. Th
20、e 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 thepetrographer concerning the source and proposed use of thematerial, and the petrographers ability to correlate these
21、 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 are qualified by education and experienceto employ such techniques for the recognition of the charac-teristic propert
22、ies 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 interpretation of the results. In others, the interpreta-tion will be made in part by engineers or others qualified torel
23、ate 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 chemical characteristicsof the material that may be observed by petrographic methodsand that have a bearing on the performa
24、nce 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 essential for proper evaluation of thesample when the constituents differ significantly in propertiesthat have a beari
25、ng 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 data or performance records are available.5.2 This guide may be used by a petrographer employeddirectly by those for wh
26、om 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 the extent of examinationdesired. Pertinent background information, including results ofprior testing, should be mad
27、e 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 purchaser of consulting petrographic serviceand the petrographer. In such a case, the purchaser and theconsultant shoul
28、d together determine the kind, extent, andobjectives of the examination and analyses to be made, andshould record their agreement in writing. The agreement maystipulate specific determinations to be made, observations to bereported, funds to be obligated, or a combination of these orother conditions
29、.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 formany other purposes. Petrographic examinations provide iden-tification of types and varieties of rocks present in pote
30、ntialaggregates. However, as noted above, identification of everyrock and mineral present in an aggregate source is not required.5.5 The petrographic examination should establish whetherthe aggregate contains chemically unstable minerals such assoluble sulfates, unstable sulfides that may form sulfu
31、ric acidor create distress in concrete exposed to high temperaturesduring service, or volumetrically unstable materials such assmectites (formerly known as the montmorillonite-saponitegroup of minerals or swelling clays). Specifications may limitthe quartz content of aggregates for use in concrete t
32、hat 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 examination should identify the portion ofeach coarse aggregate that is composed of weathered orotherwise altered particle
33、s 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 which the aggregate may be used will beexposed to freezing and thawing in a critically saturatedcondition, finely por
34、ous 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 of the concrete to fail in freezingand thawing. This will ultimately destroy the concrete becausesuch aggregates
35、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 Petrographic examinations may also be used to deter-mine the proportions of cubic, spherical, ellipsoidal, pyramida
36、l,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 decreaseconcrete strength.5.8 Petrographic examination should identify and call atten-tion to potentially alkali-sili
37、ca reactive and alkali-carbonatereactive constituents, determine such constituents quantita-tively, and recommend additional tests to confirm or refute thepresence in significant amounts of aggregate constituentscapable of alkali reaction in concrete. See Specification C33.C295082Alkali-silica react
38、ive constituents found in aggregates include:opal, chalcedony, cristobalite, tridymite, highly strained quartz,microcrystalline quartz, volcanic glass, and synthetic siliceousglass. Aggregate materials containing these constituents in-clude: glassy to cryptocrystalline intermediate to acidic volca-n
39、ic rocks, some argillites, phyllites, graywacke, gneiss, schist,gneissic granite, vein quartz, quartzite, sandstone, and chert.Criteria are available for identifying the minerals in the listabove by their optical properties or by XRD (2),(3). Criteria areavailable for identifying rocks by their mine
40、ral compositionand texture (4). Examination in both reflected and transmittedlight may be necessary to provide data for these identifications.X-ray microanalysis using energy-dispersive x-ray spectrom-eters with scanning electron microscopy (SEM/EDX) orwavelength-dispersive x-ray spectrometers in el
41、ectron micro-probes (EMPA/WDX) may 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 an
42、d 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 not necessar-ily deleterious.5.9 Petrographic examination may be directed specificallyat the possible presence of contamina
43、nts in aggregates, such assynthetic 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 con
44、taminant 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 materials for use in concrete construction havereasonable assurance that the petrographic examination resultswherever an
45、d 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 procedures described inthis guide. All specific items listed have been used, in connec-tion with the performance of petrograp
46、hic examinations, by theprocedures 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 wo
47、rk 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 serv
48、e 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 with 350-mm orlarger diamond blade, and automatic feed.6.1.1.2 Horizontal Grinding Wheel, * preferably 400 mm indiameter.6
49、.1.1.3 Polishing Wheel, preferably 200 to 300 mm indiameter.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 in size.6.1.1.7 Mounting Medium for Powder Mounts* Canadabalsam, neutral, in xylene; suitable low-viscosity epoxy resins;or Lakeside 70.6.1.1.8 Xylene*.6.1.1.9 Mounting Medium*, suitable for mounting rockslices for thin sections.6.1.1.10 Laboratory Oven*.6.1.1.11 Plate-Glass Squares*, about
