C295C295M-12 Standard Guide for Petrographic Examination of Aggregates for Concrete

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Standard Guide for Petrographic Examination of Aggregates for Concrete
  Designation: C295/C295M − 12 Standard Guide for Petrographic Examination of Aggregates for Concrete 1 This standard is issued under the fixed designation C295/C295M; the number immediately following the designation indicates the yearof srcinal adoption 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. This standard has been approved for use by agencies of the Department of Defense. 1. Scope* 1.1 This guide outlines procedures for the petrographicexamination 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) . 2 1.2 This guide outlines the extent to which petrographictechniques should be used, the selection 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 accordance 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-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 limitations prior to use. 2. Referenced Documents 2.1  ASTM Standards: 3 C33 Specification for Concrete AggregatesC117 Test Method for Materials Finer than 75-µm (No. 200)Sieve in Mineral Aggregates by WashingC136 Test Method for Sieve Analysis of Fine and CoarseAggregatesC294 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 Reflected–Light Photomicrography 3. Qualifications of Petrographers 3.1 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 course work pertaining to basic geology, mineralogy, petrography, andoptical mineralogy or have obtained equivalent knowledgethrough experience and on-the-job training. Completion of course work in concrete materials is also advantageous. Thepetrographer should have experience evaluating the effects of aggregates 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 petrographer’s experience. The petrog-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 a full-timesupervising petrographer 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 itself, consti-tute sufficient qualification for examination of aggregates forconcrete. 1 This 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 April 1, 2012. Published May 2012. Originallyapproved in 1954. Last previous edition approved in 2011 as C295/C295M–11.DOI: 10.1520/C0295_C0295M-12. 2 The boldface numbers in parentheses refer to the list of references at the end of this standard. 3 For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For  Annual Book of ASTM Standards  volume information, refer to the standard’s Document Summary page onthe ASTM website. *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 1    4. Summary of Method 4.1 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 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 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 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. 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 thepetrographer concerning the source and proposed use of thematerial, and the petrographer’s 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 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 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 Use 5.1 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 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 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 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 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 the extent of examinationdesired. Pertinent background information, including results of prior testing, should be made available. The petrographer’sadvice and judgment should be sought regarding the extent of the 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 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 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-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, 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 sulfuric 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 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 examination should identify the portion of each 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 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 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 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, 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 decreaseconcrete strength.5.8 Petrographic examination should identify and call atten-tion to potentially alkali-silica reactive and alkali-carbonatereactive constituents, determine such constituents C295/C295M − 12 2    quantitatively, and recommend 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, microcrystalline quartz, volcanic glass, andsynthetic siliceous glass. Aggregate materials containing theseconstituents include: glassy to cryptocrystalline intermediate toacidic volcanic rocks, some argillites, phyllites, graywacke,gneiss, schist, gneissic granite, vein quartz, quartzite,sandstone, and chert. Criteria are available for identifying theminerals in the list above by their optical properties or by XRD (2) , (3) . Criteria are available for identifying rocks by theirmineral composition and texture  (4) . Examination in bothreflected and transmitted light may be necessary to providedata for these identifications. X-ray microanalysis usingenergy-dispersive x-ray spectrometers with scanning electronmicroscopy (SEM/EDX) or wavelength-dispersive x-ray spec-trometers in electron microprobes (EMPA/WDX) may provideuseful information on the chemical composition of mineralsand rocks. Potentially deleterious alkali-carbonate reactiverocks are usually calcareous dolomites or dolomitic limestoneswith clayey insoluble residues. Some dolomites essentially freeof clay and some very fine-grained limestones free of clay andwith minor insoluble residue, mostly quartz, are also capable of some alkali-carbonate reactions, however, such reactions arenot necessarily 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 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 of aggregate materials for use in concrete construction havereasonable assurance that the petrographic examination resultswherever and whenever obtained may confidently be com-pared. 6. Apparatus and Supplies 6.1 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; 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 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 [14-in.] diameter or larger diamond blade, and automatic feed.6.1.1.2  Horizontal Grinding Wheel,  * preferably 400-mm[16-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 µm],220 [63 µm], 320 [31 µm], 600 [16 µm], and 800 [12 µm];alumina M-305 [5 µm]. 4 6.1.1.5  Geologist’s 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 resins;or Lakeside 70.6.1.1.8  Xylene*. 6.1.1.9  Mounting Medium*,  suitable for mounting rock slices for thin sections.6.1.1.10  Laboratory Oven*. 6.1.1.11  Plate-Glass Squares*,  about 300 mm [12 in.] on anedge for thin-section grinding.6.1.1.12  Sample Splitter   with pans.*6.1.1.13  Micro Cover Glasses,  * noncorrosive, square, 12 to18 mm, 25 mm, [0.5 to 0.75 in., 1.0 in.] etc.6.1.1.14  Plattner Mortar. 6.1.2  Apparatus and Supplies for Examination of Speci-mens: 6.1.2.1  Petrographic Microscope*,  with mechanical stage;oculars and objective lenses that will allow magnifications of up to 600 x, and objective-centering devices; full- and quarter-wave compensators; quartz wedge; micrometer eyepiece; Ber-trand lens.6.1.2.2  Microscope Lamps* 6.1.2.3  Stereoscopic Microscope*,  with objectives and ocu-lars to give final magnifications from about 6× to about 150×.6.1.2.4  Magnet*,  preferably Alnico, or an electromagnet.6.1.2.5  Needleholder and Points*. 6.1.2.6  Dropping Bottle,  60-mL [2 oz.] capacity.6.1.2.7  Petri Culture Dishes. 6.1.2.8  Forceps,  smooth, straightpointed.6.1.2.9  Lens Paper.* 6.1.2.10  Immersion Media*, n  = 1.410 to  n  = 1.785 insteps of no more than 0.005.6.1.2.11  Counter. 6.1.2.12  Photomicrographic Camera  and accessories.6.2 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 journals. 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. 4 The values given in micrometres are the approximate average grain size of commercial silicon carbide grit in the designated size classification. C295/C295M − 12 3    6.3 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 will not be stable for very long periods of timeand are subject to considerable variation due to temperaturechange. In laboratories not provided with close temperaturecontrol, it is often necessary to recalibrate immersion mediaseveral times during the course of a single day when accurateidentifications are required. The equipment needed for check-ing immersion media consists of an Abbé refractometer. Therefractometer should be equipped with compensating prisms toread indices for sodium light from white light, or it should beused with a sodium arc lamp.6.4 Alaboratory that undertakes any considerable amount of petrographic work should be provided with facilities to makephotomicrographic records of such features as cannot ad-equately be described in words. For illustrations of typicalapparatus, reference may be made to Ref   (1)  and manufacturersof microscopes equipped with cameras and photomacrographicequipment may be consulted. Much useful guidance regardingphotomicrography, especially using reflected light, is found inGuide E883. 7. Sampling 7.1 Samples for petrographic examination should be takenby or under the direct supervision of a geologist familiar withthe requirements for random sampling of aggregates forconcrete and in general following the requirements of PracticeD75. Information on the exact location from which the samplewas taken, the geology of the site, and other pertinent datashould be submitted with the sample. The amount of materialactually studied in the petrographic examination will bedetermined by the nature of the examination to be made and thenature of the material to be examined, as discussed below.7.1.1  Undeveloped quarries  should be sampled by means of cores drilled through the entire depth expected to be exploited.Drilling of such cores should be in a direction that is essentiallyperpendicular to the dominant structural feature of the rock.Massive material may be sampled by “NX” (50-mm [2-in.]diameter) cores. Thinly bedded or complex material should berepresented by cores not less than 100 mm [4 in.] in diameter.There should be an adequate number of cores to cover thelimits of the deposit proposed for the project. The entirefootage of the recovered core should be included in the sampleand accurate data given as to elevations, depths, and corelosses.7.1.2  Operating quarries and operating sand and graveldeposits,  in which stock piles of the material produced areavailable, should be represented by not less than 45 kg [100 lb]or 300 pieces, whichever is larger, of each size of material tobe examined. Samples from stock piles should be composed of representative portions of larger samples collected with dueconsideration given to segregation in the piles.7.1.3  Exposed faces of nonproducing quarries,  where stock piles of processed material are not available, should berepresented by not less than 2 kg [4 lb] from each distinctivestratum or bed, with no piece having a mass less than 0.5 kg [1lb], or by a drilled core as described above.7.1.4  Undeveloped sand and gravel deposits  should besampled by means of test pits dug to the anticipated depth of future economic production. Samples should consist of not lessthan the quantities of material indicated in Table 1, selected soas to be representative of the deposits. NATURAL GRAVEL AND SAND8. Procedure 8.1  Selection of Samples for Examination—  Samples of gravel and natural sand for petrographic examination should bedry sieved in accordance with Method C136 to providesamples of each sieve size. In the case of sands an additionalportion should then be tested in accordance with Test MethodC117, with the wash water being saved and removed by dryingin order to provide a sample of the material passing the 75-µm(No. 200) sieve (See Specification E11). 5 The results of thesieve analysis of each sample made in accordance with MethodC136 should be provided to the petrographer making theexamination and used in calculating results of the petrographicexamination. Each sieve fraction should be examinedseparately, starting with the largest size available. Rocks aremore easily recognized in larger pieces; the breakdown of aheterogeneous type present in the larger sizes may haveprovided particles of several apparently different types in thesmaller sizes. Some important and easily confused types maybe recognizable using the stereoscopic microscope if they arefirst recognized and separated in the larger sizes, but mayrequire examination using the petrographic microscope if theyare first encountered in the smaller sizes.8.2 The number of particles of each sieve fraction to beexamined will be fixed by the required precision of determi-nation of the less abundant constituents. Assuming that thefield sampling and laboratory sampling procedures are accurateand reliable, the number of particles examined, identified, andcounted in each sieve fraction will depend on the requiredaccuracy of the estimate of constituents present in small 5 Sieve size is identified by its standard designation in Specification E11. The alternative designation given in parentheses is for information only and does notrepresent a different standard sieve size. TABLE 1 Minimum Sizes for Samples from Undeveloped Sandand Gravel Deposits Sieve SizeQuantitykg [lb] PiecesLarger than 150-mm (6-in.) A ... ...  B  75 to 150-mm (3 to 6-in.) A ... ... 300 B  37.5 to 75-mm (1 1  ⁄  2  to 3-in.) A 180 [400] ...19.0 to 37.5-mm ( 3  ⁄  4  to 1 1  ⁄  2 -in.) A 90 [200] ...4.75 to 19.0-mm (No. 4 to  3  ⁄  4 -in.) A 45 [100] ...Finer than 4.75-mm (No. 4) A , C  23 [50] ... A Sieve size is identified by its standard designation in Specification E11. The alternative designation given in parentheses is for information only and does notrepresent a different standard sieve size. B  Not less than one piece from each apparent type of rock. C  Fine aggregate. C295/C295M − 12 4  
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