1、Designation: C 295 03Standard 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 (e) 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. Scope1.1 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 provided forinformation purposes only.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
6、 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:C 33 Specification for Concrete Aggregates3C 117 Test Method for Materials Finer than 75-m (No.200) Sieve in Mineral Aggre
7、gates by Washing3C 136 Test Method for Sieve Analysis of Fine and CoarseAggregates3C 294 Descriptive Nomenclature for Constituents of Con-crete Aggregates3C 702 Practice for Reducing Samples of Aggregate toTesting Size3D 75 Practice for Sampling Aggregates4E 11 Specification for Wire Cloth and Sieve
8、s for TestingPurposes5E 883 Guide for Reflected-Light Photomicrography63. Summary of Method3.1 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
9、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, differential thermal an
10、alysis (DTA), infrared spectros-copy, or other scanning electron microscopy (SEM) energy-dispersive x-ray analysis (EDX). In some instances, suchprocedures are more rapid and more definitive than aremicroscopical methods.3.2 Identification of the constituents of a sample is usually anecessary step t
11、owards 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, the com-pletenes
12、s 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.3.3 This guide does not attempt to describe the techniquesof petrographic work since it is as
13、sumed 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 petrographer will have
14、 had experience adequate to provide1This 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 Jan. 10, 2003. Published March 2003. Originallyapproved in 1954. Last previ
15、ous edition approved in 1998 as C 295-98.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3Annual Book of ASTM Standards, Vol 04.02.4Annual Book of ASTM Standards, Vol 04.03.5Annual Book of ASTM Standards, Vol 14.02.6Annual Book of ASTM Standards, Vol 0
16、3.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.detailed 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 answer
17、ed.4. Significance and Use4.1 Petrographic examinations are made for the followingpurposes:4.1.1 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.4.1.2 To de
18、scribe and classify the constituents of thesample,4.1.3 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 bearing on the performance of the material in itsintend
19、ed use, and4.1.4 To compare samples of aggregate from new sourceswith samples of aggregate from one or more sources, for whichtest data or performance records are available.4.2 This guide may be used by a petrographer employeddirectly by those for whom the examination is made. Theemployer should tel
20、l 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 made available. The petrographersadvice and judgment
21、should be sought regarding the extent ofthe examination.4.3 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 should together determine the kind, extent, andobjectiv
22、es 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.4.4 Petrographic examination of aggregate conside
23、red 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 potentialaggregates. However, as noted above, identifi
24、cation of everyrock and mineral present in an aggregate source is not required.4.5 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
25、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 that may besubject to high temperature (purposefull
26、y or accidentally)because of the conversion to beta-quartz at 573C (1063F),with accompanying volume increase.4.6 Petrographic examination should identify the portion ofeach coarse aggregate that is composed of weathered orotherwise altered particles and the extent of that weathering oralteration, wh
27、ether 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 porous and highly weathered or otherwisealtered rocks s
28、hould 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 cannot be protected by adequately air-entrained mort
29、ar. Finely porous aggregates near the concretesurface are also likely to form popouts, which are blemishes onpavements and walls.4.7 Petrographic examinations may also be used to deter-mine the proportions of cubic, spherical, ellipsoidal, pyramidal,tabular, flat, and elongated particles in an aggre
30、gate sample orsamples. Flat, elongated, and thin chip-like particles in aggre-gate increase the mixing water requirement and hence decreaseconcrete strength.4.8 Petrographic examination should identify and call atten-tion to potentially alkali-silica reactive and alkali-carbonatereactive constituent
31、s, 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 C 33.Alkali-silica reactive constituents found in aggregates include:opal, chalced
32、ony, 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-nic rocks, some argillites, phyllites, graywacke, gneiss, s
33、chist,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 mineral compositionand texture (4). Examination in both reflec
34、ted 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 electron micro-probes (EMPA/WDX) may provide useful informat
35、ion 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 limestones free of clay and with m
36、inor insolubleresidue, mostly quartz, are also capable of some alkali-carbonate reactions, however, such reactions are not necessar-ily deleterious.4.9 Petrographic examination may be directed specificallyat the possible presence of contaminants in aggregates, such assynthetic glass, cinders, clinke
37、r, 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-sirable in concrete.C2950324.
38、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 confidently be com-pared.5.
39、 Apparatus and Supplies5.1 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 theprocedures described herein
40、; 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
41、 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 purpose, thatare indicated by asterisks
42、in the lists given as follows.5.1.1 Apparatus and Supplies for Preparation of Specimens:5.1.1.1 Rock-Cutting Saw, * preferably with 350-mm orlarger diamond blade, and automatic feed.5.1.1.2 Horizontal Grinding Wheel, * preferably 400 mm indiameter.5.1.1.3 Polishing Wheel, preferably 200 to 300 mm in
43、diameter.5.1.1.4 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).75.1.1.5 Geologists Pick or Hammer.5.1.1.6 Microscope Slides*, clear, noncorrosive, 25 by 45mm in size.5.1.1.7 Mounting Medium for Powder Mounts* Canadabalsam, neut
44、ral, in xylene; suitable low-viscosity epoxy resins;or Lakeside 70.5.1.1.8 Xylene*.5.1.1.9 Mounting Medium*, suitable for mounting rockslices for thin sections.5.1.1.10 Laboratory Oven*.5.1.1.11 Plate-Glass Squares*, about 300 mm on an edgefor thin-section grinding.5.1.1.12 Sample Splitter with pans
45、.*5.1.1.13 Micro Cover Glasses, * noncorrosive, square, 12 to18 mm, 25 mm, etc.5.1.1.14 Plattner Mortar.5.1.2 Apparatus and Supplies for Examination of Speci-mens:5.1.2.1 Petrographic Microscope*, with mechanical stage;oculars and objective lenses that will allow magnifications ofup to 600 x, and ob
46、jective-centering devices; full- and quarter-wave compensators; quartz wedge; micrometer eyepiece; Ber-trand lens.5.1.2.2 Microscope Lamps*5.1.2.3 Stereoscopic Microscope*, with objectives and ocu-lars to give final magnifications from about 63 to about 1503.5.1.2.4 Magnet*, preferably Alnico, or an
47、 electromagnet.5.1.2.5 Needleholder and Points*.5.1.2.6 Dropping Bottle, 60-mL capacity.5.1.2.7 Petri Culture Dishes.5.1.2.8 Forceps, smooth, straightpointed.5.1.2.9 Lens Paper.*5.1.2.10 Immersion Media*, n = 1.410 to n = 1.785 insteps of no more than 0.005.5.1.2.11 Counter.5.1.2.12 Photomicrographi
48、c Camera and accessories.5.2 The items under Apparatus and Supplies include thoseused to make thin sections. Semiautomatic thin section ma-chines are available, and there are several thin-section makerswho advertise in Geotimes, the American Mineralogist, andother mineralogical or geological journal
49、s. Laboratories mayfind it reasonable to buy a thin-section machine or use acommercial thin-section maker. Remotely located laboratorieshave more need to be able to make their own thin sections.5.3 It is necessary that facilities be available to the petrog-rapher to check the index of refraction of the immersion media.If accurate identification of materials is to be attempted, as forexample the differentiation of quartz and chalcedony, or thedifferentiation of basic from intermediate volcanic glass, theindices of refraction of the media need to be known withaccuracy. Media w
