ASTM C856/C856M-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C856/C856M − 20
Standard Practice for
Petrographic Examination of Hardened Concrete
This standard is issued under the fixed designation C856/C856M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
fication E11. The alternative designation given in parentheses is for
1. Scope*
information only and does not represent a different standard sieve size.
1.1 This practice outlines procedures for the petrographic
1.5 This standard does not purport to address all of the
examination of samples of hardened concrete. The samples
safety concerns, if any, associated with its use. It is the
examined may be taken from concrete constructions, they may
responsibility of the user of this standard to establish appro-
be concrete products or portions thereof, or they may be
priate safety, health, and environmental practices and deter-
concreteormortarspecimensthathavebeenexposedinnatural
mine the applicability of regulatory limitations prior to use. A
environments, or to simulated service conditions, or subjected
specific hazard statement is given in 6.2.10.1.
to laboratory tests. The phrase “concrete constructions” is
1.6 This international standard was developed in accor-
intended to include all sorts of objects, units, or structures that
dance with internationally recognized principles on standard-
have been built of hydraulic cement concrete.
ization established in the Decision on Principles for the
1.2 The petrographic procedures outlined herein are appli-
Development of International Standards, Guides and Recom-
cable to the examination of samples of all types of hardened
mendations issued by the World Trade Organization Technical
mixtures, including concrete, mortar, grout, plaster, stucco,
Barriers to Trade (TBT) Committee.
terrazzo, and the like. In this practice, the material for
2. Referenced Documents
examination is designated as “concrete,” even though the
commentary may be applicable to the other mixtures, unless
2.1 ASTM Standards:
the reference is specifically to media other than concrete.
C125Terminology Relating to Concrete and Concrete Ag-
gregates
1.3 Thepurposesofandproceduresforpetrographicexami-
C215 Test Method for Fundamental Transverse,
nationofhardenedconcretearegiveninthefollowingsections:
Longitudinal, and Torsional Resonant Frequencies of
Section
Concrete Specimens
Qualifications of Petrographers and Use of Technicians 4
C452Test Method for Potential Expansion of Portland-
Purposes of Examination 5
Cement Mortars Exposed to Sulfate
Apparatus 6
C457Test Method for Microscopical Determination of Pa-
Selection and Use of Apparatus 7
Samples 8
rameters of the Air-Void System in Hardened Concrete
Examination of Samples 9
C597Test Method for Pulse Velocity Through Concrete
Specimen Preparation 10
C803/C803MTest Method for Penetration Resistance of
Visual and Stereomicroscope Examination 11
Polarizing Microscope Examination 12
Hardened Concrete
Paste Features 13
C805Test Method for Rebound Number of Hardened Con-
Report 14
crete
1.4 The values stated in either SI units or inch-pound units
C823Practice for Examination and Sampling of Hardened
are to be regarded separately as standard. The values stated in
Concrete in Constructions
eachsystemarenotnecessarilyexactequivalents;therefore,to
C1012 Test Method for Length Change of Hydraulic-
ensure conformance with the standard, each system shall be
Cement Mortars Exposed to a Sulfate Solution
used independently of the other, and values from the two
C1723Guide for Examination of Hardened Concrete Using
systems shall not be combined.
Scanning Electron Microscopy
NOTE 1—Sieve size is identified by its standard designation in Speci-
E3Guide for Preparation of Metallographic Specimens
E11Specification forWovenWireTest Sieve Cloth andTest
Sieves
This practice is under the jurisdiction of ASTM Committee C09 on Concrete
andConcreteAggregatesandisthedirectresponsibilityofSubcommitteeC09.65on
Petrography. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 15, 2020. Published February 2020. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1977. Last previous edition approved in 2018 as C856–18a. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0856_C0856M-20. the 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
C856/C856M − 20
E883Guide for Reflected–Light Photomicrography determinations to be made, observations to be reported, funds
tobeobligated,oracombinationoftheseandotherconditions.
3. Terminology
5. Purposes of Examination
3.1 Definitions: For definitions of terms used in this
practice, refer to Terminology C125.
5.1 Examples of purposes for which petrographic examina-
tion of concrete is used are given in 5.2 – 5.5. The probable
4. Qualifications of Petrographers and Use of Technicians
usefulness of petrographic examination in specific instances
may be determined by discussion with an experienced petrog-
4.1 All petrographic examinations of hardened concrete
described in this practice shall be performed by or under the rapher of the objectives of the investigation proposed or
underway.
technical direction of a full time supervising petrographer with
at least five years experience in petrographic examinations of
5.2 Concrete from Constructions:
concrete and concrete-making materials. The supervising con-
5.2.1 Determination in detail of the condition of concrete in
crete petrographer shall have college level courses that include
a construction.
petrography, mineralogy, and optical mineralogy, or five years
5.2.2 Determination of the causes of inferior quality,
of documented equivalent experience, and experience in their
distress, or deterioration of concrete in a construction.
application to evaluations of concrete-making materials and
5.2.3 Determination of the probable future performance of
concrete products in which they are used and in cementitious-
the concrete.
based materials.Aresume of the professional background and
5.2.4 Determination whether the concrete in a construction
qualifications of all concrete petrographers shall be available.
was or was not as specified. In this case, other tests may be
4.2 A concrete petrographer shall be knowledgeable about required in conjunction with petrographic examination.
the following: concrete-making materials; processes of
5.2.5 Description of the cementitious matrix, including
batching, mixing, handling, placing, and finishing of concrete;
qualitative determination of the kind of binder used, degree of
the composition and microstructure of cementitious paste; the
hydration, degree of carbonation if present, evidence of un-
interaction of constituents of concrete; and the effects of
soundness of the cement, presence of supplementary cementi-
exposure of such concrete to a wide variety of conditions of
tious materials, the nature of the hydration products, adequacy
service.
of curing, and unusually high water–cement ratio of the paste.
5.2.6 Determination whether alkali–silica or alkali–carbon-
4.3 Sample preparation shall be performed by concrete
ate reactions, or cement–aggregate reactions, or reactions
petrographers or trained technicians pursuant to instructions
between contaminants and the matrix have taken place, and
from and under the guidance of a qualified concrete petrogra-
their effects upon the concrete.
pher. Aspects of the petrographic examination, such as the
5.2.7 Determination whether the concrete has been sub-
measurement of sample dimensions, photography of as-
jected to and affected by sulfate attack, or other chemical
received samples, staining of sample surfaces, that do not
attack, or early freezing, or to other harmful effects of freezing
require the education and skills outlined in 4.1, shall be
and thawing.
performed by concrete petrographers or by trained technicians
5.2.8 Part of a survey of the safety of a structure for a
pursuant to instructions and under the guidance of a qualified
present or proposed use.
concrete petrographer. The analysis and interpretation of the
5.2.9 Determination whether concrete subjected to fire is
features that are relevant to the investigation and evaluation of
essentially undamaged or moderately or seriously damaged.
the performance of the materials represented by the sample
5.2.10 Investigationoftheperformanceofthecoarseorfine
shall be made solely by concrete petrographers with qualifica-
aggregate in the structure, or determination of the composition
tions consistent with those outlined in 4.1.
of the aggregate for comparison with aggregate from approved
4.4 Aconcrete petrographer shall be prepared to provide an
or specified sources.
oral statement, written report, or both that includes a descrip-
5.2.11 Determination of the factors that caused a given
tion of the observations and examinations made during the
concrete to serve satisfactorily in the environment in which it
petrographic examinations, and interpretation of the findings
was exposed.
insofar as they relate to the concerns of the person or agency
5.2.12 Determination of the presence and nature of surface
for whom the examination was performed. Supplementary
treatments, such as dry shake applications on concrete floors.
information provided to the petrographer on the concrete and
5.3 Test Specimens from Actual or Simulated Service—
concrete materials, conditions of service, or other features of
the concrete construction may be helpful in interpreting the Concrete or mortar specimens that have been subjected to
actual or simulated service conditions may be examined for
data obtained during the petrographic examinations.
mostofthepurposeslistedunderConcretefromConstructions.
4.5 This practice may form the basis for establishing ar-
5.4 Concrete Products:
rangements between a purchaser of the consulting service and
theconsultingpetrographer.Insuchcases,thepurchaserofthe 5.4.1 Petrographic examination can be used in investigation
consulting service and the consulting petrographer should of concrete products of any kind, including masonry units,
together determine the kind, extent, and objectives of the precaststructuralunits,piling,pipe,andbuildingmodules.The
examinations and analyses to be made, and may record their productsorsamplesofthosesubmittedforexaminationmaybe
agreement in writing. The agreement may stipulate specific either from current production, from elements in service in
C856/C856M − 20
constructions, or from elements that have been subjected to generally used. Equipment required for field sampling is not
tests or to actual or simulated service conditions. listed. Any other useful equipment may be added.
5.4.2 Determination of features like those listed under
6.2 For Specimen Preparation:
concrete from constructions.
6.2.1 Diamond Saw—Slabbing saw with an automatic feed
5.4.3 Determination of effects of manufacturing processes
and blade large enough to make at least a 175-mm [7-in.] cut
and variables such as procedures for mixing, molding,
in one pass.
demolding, consolidation, curing, and handling.
6.2.2 Cutting Lubricant, for diamond saw.
5.4.4 Determination of effects of use of different concrete-
6.2.3 Horizontal Lap Wheel or Wheels, steel, cast iron, or
making materials, forming and molding procedures, types and
othermetallap,preferablyatleast400mm[16in.]indiameter,
amounts of reinforcement, embedded hardware, and so forth.
large enough to grind at least a 100 by 150-mm [4 by 6-in.]
5.5 Laboratory Specimens—The purposes of petrographic
area.
examination of laboratory specimens of concrete, mortar, or
6.2.4 Free Abrasive Machine, using abrasive grit in
cementpasteare,ingeneral,toinvestigatetheeffectsofthetest
lubricant,withsampleholdersrotatingonarotatingtable.This
on the test piece or on one or more of its constituents, to
type of grinding machine greatly increases the speed of
provideexamplesoftheeffectsofaprocess,andtoprovidethe
preparation of finely ground surfaces.
petrographer with visual evidence of examples of reactions in
6.2.5 Polishing Wheel, at least 200 mm [8 in.] in diameter
paste or mortar or concrete of known materials, proportions,
and preferably two-speed, or a vibratory polisher.
age, and history. Specific purposes include:
6.2.6 Hot Plate or Oven, thermostatically controlled, to
5.5.1 To establish whether alkali–silica reaction has taken
permit drying and impregnating specimens with resin or wax
place, what aggregate constituents were affected, what evi-
for preparing thin sections, ground surfaces, and polished
dence of the reaction exists, and what were the effects of the
sections.
reaction on the concrete.
6.2.7 Prospector’s Pick or Bricklayer’s Hammer, or both.
5.5.2 To establish whether one or more alkali–carbonate
6.2.8 Abrasives—Silicon carbide grits, No. 100 (150-µm),
reactions have taken place, which aggregate constituents were
No. 220 (63-µm), No. 320 (31-µm), No. 600 (16-µm), No. 800
affected and what evidence of the reaction or reactions exists,
(12-µm); optical finishing powders, such as M-303, M-204,
and the effects of the reaction on the concrete properties.
M-309; polishing powders as needed.
5.5.3 To establish whether any other cement– aggregate
6.2.9 Plate-glass Squares, 300 to 450 mm [12 to 18 in.] on
reaction has taken place. In addition to alkali–silica and
an edge and at least 10 mm [ ⁄8 in.] thick for hand-finishing
alkali–carbonate reactions, these include hydration of anhy-
specimens.
drous sulfates, rehydration of zeolites, wetting of clays and
6.2.10 Suitable Medium or Media, for impregnating con-
reactions involving solubility, oxidation, sulfates, and sulfides
3 crete and mounting thin sections plus appropriate solvent.
(see Refs (1-3)).
Canada balsam, Lakeside 70 cement, and flexibilized epoxy
5.5.4 To establish whether an aggregate used in a test has
formulations have been used.
been contaminated by a reactive constituent when in fact the
6.2.10.1 Warning—Flexibilized epoxies form strong bonds
aggregate was not reactive.
but have higher indexes of refraction than Canada balsam or
5.5.5 To establish the effects of a freezing and thawing test
Lakeside 70 and are toxic. Do not allow to touch the skin;
or other physical or mechanical exposure of concrete on the
plastic gloves shall be worn, and the work shall be done under
aggregate and the matrix.
a hood so as not to breathe the fumes.
5.5.6 To establish the extent of reaction, the nature of
6.2.11 Microscope Slides—Clear, noncorrosive, glass ap-
reactionproducts,andeffectsofreactionproducedinexposure
15 3
proximately24mm[ ⁄16in.]wideandatleast45mm[1 ⁄4in.]
toachemicallyaggressiveenvironmentsuchasinTestMethod
long. Thickness may need to be specified to fit some thin
C452 or Test Method C1012.
section machines.
5.5.7 To determine the characteristics of moist-cured con-
6.2.12 Cover Glasses, noncorrosive and preferably No. 1
crete that has not been subjected to chemical attack or
(0.18-mm) thickness.
cement–aggregate reaction or freezing and thawing.
5.5.8 By comparison with appropriate laboratory
6.3 For Specimen Examination:
specimens, a petrographer may be able to substantiate the
6.3.1 Stereomicroscope, providing magnifications in the
existence of a particular reaction in concrete or determine that
range from 7× to 70× or more.
the reaction cannot be detected.
6.3.2 Dollies—Small, wheeled dollies with flat tops and
withtopscurvedtoholdasectionofcoreassistinmanipulating
6. Apparatus
concrete specimens under the stereomicroscope.
6.1 The apparatus and supplies employed in making petro-
6.3.3 Petrographic Microscope or Polarizing Microscope,
graphic examinations of hardened concrete depend on the
for examinations in transmitted light, with mechanical stage;
proceduresrequired.Thefollowinglistincludestheequipment
low-, medium-, and high-power objectives such as 3.5×, 10×,
and20to25×;43to50×withnumericalaperture0.85ormore;
assorted eyepieces having appropriate corrections and magni-
fications for use with each of the objectives; micrometer
The boldface numbers in parentheses refer to a list of references at the end of
this standard. eyepiece; condenser adjustable to match numerical aperture of
C856/C856M − 20
objectivewithhighestnumericalaperturetobeused;full-wave 7.2 The minimum equipment for petrographic examination
and quarter-wave compensators, quartz wedge, and other of concrete where both specimen preparation and examination
accessories. are completed within the laboratory consists of a selection of
6.3.4 Metallographic Microscope, with vertical illuminator, apparatus and supplies for specimen preparation, a stereomi-
croscope preferably on a large stand so that 150-mm [6-in.]
mechanical stage, metallographic objectives of low, medium,
andhighmagnification,andappropriateeyepiecestoprovidea diameter cores can be conveniently examined, a polarizing
microscope and accessories, lamps for each microscope, and
range of magnifications from about 25× to 500×. Reflected
polarized light should be available and appropriate compensa- stable calibrated immersion media of known thermal coeffi-
cient. Specimens for petrographic examination may be ob-
tors provided. Some polarizing microscopes can be equipped
with accessories for metallographic examination, if the tube tained by sending samples to individuals or firms that offer
custom services in preparing thin or polished sections and
can be raised or the stage lowered to give adequate clearance
for the vertical illuminator and the thicker specimens usually finely ground surfaces. It is more convenient to prepare
specimens in house, and their prompt availability overrides
employed.
their probably greater cost.
6.3.5 Eyepiece Micrometer—Eyepiece micrometers cali-
brated using a stage micrometer are useful for measuring
7.3 X-ray diffraction, X-ray emission, differential thermal
particles of aggregate, cement grains, calcium hydroxide and
analysis, thermogravimetric analysis, analytical chemistry, in-
other crystals, and crack widths.
frared spectroscopy, scanning electron microscopy, energy or
6.3.6 Stage Micrometer, to calibrate eyepiece micrometers.
wavelength dispersive analysis, and other techniques may be
6.3.7 Microscope Lamps—Many modern polarizing micro-
very useful in obtaining quick and definite answers to relevant
scopes have built-in illuminators which are convenient and
questions where microscopy will not do so. Some undesirable
satisfactory if, with the condenser, they can be adjusted to fill
constituents of concrete, some hydration products of cement,
the back lens of the objective of highest numerical aperture
and some reaction products useful in defining the effects of
with light. If the microscope requires a separate illuminator,
different exposures, and many contaminating materials may
tungsten ribbon-filament bulbs in suitable adjustable housings
not be identified unless techniques that supplement light
are satisfactory. Many kinds of illuminators are available for
microscopy are used. (4, 5).
stereomicroscopes; some can be mounted on the microscope,
8. Samples
some stand on their own bases; choice is a question of
adequacy of illumination for the tasks intended. Focusable
8.1 The minimum size of sample should amount to at least
illuminators are preferred.
one core, preferably 150 mm [6 in.] in diameter and 300 mm
6.3.8 Needleholders and Points—In addition to pin vises
[1 ft] long for each mixture or condition or category of
and needles from laboratory supply houses, a No. 10 sewing
concrete, except that in the case of pavement the full depth of
needle mounted in a handle or a selection of insect pins from
pavement shall be sampled with a 100 or 150-mm [4 or 6-in.]
size 00 to size 4 are useful for prying out reaction products.
core. Broken fragments of concrete are usually of doubtful use
6.3.9 Bottles with Droppers, for acid, water, and other
in petrographic examination, because the damage to the con-
reagents applied during examination.
crete cannot be clearly identified as a function of the sampling
6.3.10 Assorted Forceps, preferably stainless steel, includ-
technique or representative of the real condition of the con-
ing fine-pointed watchmaker’s forceps.
crete. Cores smaller in diameter than 150 mm [6 in.] can be
6.3.11 Lens Paper.
used if the aggregate is small enough; in deteriorated concrete,
6.3.12 Refractometer, and Immersion Media, covering the
core recovery is much poorer with 54-mm [2 ⁄8-in.] diameter
rangeofrefractiveindexesfrom1.410toatleast1.785,insteps
core than with 150-mm [6-in.] diameter core. While it is
not larger than 0.005. Stable immersion media, calibrated at a
desirable in examination and testing to have a core three times
known temperature and of known thermal coefficient, are
the maximum size of aggregate, this circumstance is a rare
preferable and should be used in a temperature-controlled
occurrencewhenconcretewithaggregatelargerthan50mm[2
room. A thermometer graduated in tenths of a degree Celsius
in.] is sampled, because of the cost of large bits and the
shouldbeusedtomeasureairtemperaturenearthemicroscope
problems of handling large cores.
stage so that thermal corrections of refractive index can be
8.2 Samples from Constructions—The most useful samples
made if needed.
for petrographic examination of concrete from constructions
are diamond-drilled cores with a diameter at least twice (and
7. Selection and Use of Apparatus
preferably three times) the maximum size of the coarse
7.1 Laboratories should be equipped to provide aggregate in the concrete. If 150-mm [6-in.] aggregate is used,
photographs, photomacrographs, and photomicrographs to il- acoreatleast250mm[10in.]indiameterisdesirable;usually
lustrate significant features of the concrete. While ordinary a 150-mm [6-in.] diameter core is the largest provided.
microscopelampsaresometimessatisfactoryforphotomicrog- 8.2.1 The location and orientation of all cores, including
raphy in transmitted and reflected light, lamps providing cores or core lengths not sent to the laboratory, should be
intense point or field sources, such as tungsten ribbon-filament clearly shown; and each core should be properly labeled. For
bulbs, or zirconium or carbon arcs, are highly desirable. For verticallydrilledcores,theelevationordepthattopandbottom
much useful guidance regarding photomicrography, especially of each section should be shown, and core loss and fractures
using reflected light, see Guide E883. antedating the drilling should be marked. For cores taken
C856/C856M − 20
horizontallyorobliquely,thedirectionoftheverticalplaneand guidedbytheobjectivesofthestudy.TestMethodC457should
the tops and bottoms should be marked. A field log should be be referred to for those relevant subjects not described here.
provided.
9.2 Visual Examination and Outline of Additional
8.2.2 Brokenpiecesofconcretefromextremelydeteriorated
Examination—The petrographic examination should begin
structures or pieces removed while preparing for repair work
with a review of all the available information about the
aresometimesusedforpetrographicexamination.Thesamples
submitted samples followed by a visual examination of each
will be more useful if their original locations in the structure
sample.Anoutlineofinformationthatcanbeobtainedisgiven
are clearly described or indicated in a sketch or photographs.
in Table 1. That study should be followed by an examination
8.2.3 The information provided with the samples should
usingastereomicroscope(seeTable2andthesectiononVisual
include:
and Stereomicroscopic Examination). In some cases, further
8.2.3.1 The location and original orientation of each speci-
study is unnecessary, and a report can be prepared. In other
men (see Practice C823),
cases, specimens are chosen during the visual and stereomi-
8.2.3.2 The mixture proportions of the concrete or
croscope examination for further processing and additional
concretes,
stereomicroscope study, more detailed examination using the
8.2.3.3 Sources of concrete-making materials and results of petrographicormetallographicmicroscopes,scanningelectron
tests of samples thereof, microscope (SEM), or by X-ray diffraction and other instru-
mental methods, and for other chemical or physical tests.
8.2.3.4 Description of mixing, placing, consolidation, and
MethodsforspecimenpreparationareoutlinedintheSpecimen
curing methods,
Preparation Section. Table 2 and Table 3 summarize charac-
8.2.3.5 Age of the structure, or in case of a structure that
teristics of concrete conveniently observed with
required several years to complete, dates of placement of the
stereomicroscopic, petrographic, and metallographic micro-
concrete sampled,
scopes. Examination using a stereomicroscope is outlined in
8.2.3.6 Conditions of operation and service exposure,
the Visual and Stereomicroscopic Examination Section. Ex-
8.2.3.7 The reason for and objectives of the examination,
amination using a polarizing microscope is outlined in the
8.2.3.8 Symptoms believed to indicate distress or
Polarizing Microscope Examination Section; examination us-
deterioration, and
ing a metallographic microscope is outlined in the Metallo-
8.2.3.9 Results of field tests such as measurements of pulse
graphicMicroscopeExaminationSection.Examinationusinga
velocity (Test Method C215), rebound hammer numbers (Test
scanning electron microscope is outlined in Guide C1723.
Method C805) or probe readings (Test Method C803/C803M).
Observations possible using different kinds of microscopes are
8.3 Samples from Test Specimens from Natural Exposures,
shown in Table 4; properties of some relevant compounds are
Concrete Products, and Laboratory Specimens:
listed in Table 5.
8.3.1 Information provided should include: materials used,
9.3 Photographs—Photographsandimagesshouldbemain-
mixture proportions, curing, age of concrete when placed in
tainedtoillustratefeaturesoftheexaminedspecimens,suchas
service or test, orientation in exposure, present age, condition
as-received conditions before they are altered, and important
surveys during exposure, characteristics of the natural or
macro-and micro-features of prepared lapped sections, pol-
laboratory exposure, and method of manufacture of concrete
ishedsections,fracturedsurfaces,thinsections,andimmersion
products. Large concrete products may be sampled like con-
mounts. Photographs should have a scale or reference to scale.
structions; smaller ones may be represented by one or more
showing the range of condition from service or fabrication or
10. Specimen Preparation
both.
10.1 Preparation for Visual and Stereomicroscope Exami-
8.3.2 The exposure of laboratory specimens should be
nation:
described with test results, age at test and available test results
10.1.1 Diamond-drilled cores, formed or finished surfaces,
on the aggregates, binders, and admixtures used. This infor-
freshly broken surfaces, or old crack surfaces should be
mation should accompany test specimens from natural expo-
examined in the condition received. It is sometimes helpful to
sures and concrete products or samples therefrom, if available.
have drilled surfaces and formed and finished surfaces wetted
to increase contrast.
9. Examination of Samples
10.1.2 Diamondsawcutsshouldbeorientedwithrelationto
9.1 Choice of Procedures—Specific techniques and proce- significant features of the concrete, either normal to the
dures employed in examination of a sample depend on the bedding directions in conventional concrete, or normal to a
purpose of the examination and the nature of the sample. formed or finished surface, or to a crack or crack system, in
Procedurestobeusedshouldbechosenafterthequestionsthat order to reveal the structure and fabric of the concrete and the
the examination is intended to answer have been clearly extent of alteration outward from the crack.
formulated. The procedures should be chosen to answer those 10.1.3 It is useful to prepare at least one sawed surface by
questions as unequivocally and as economically as possible. grinding it with progressively finer abrasives (as described in
The details that need to be resolved will be dictated by the Test Method C457) until a smooth matte finish is achieved and
objectives of the examination and will vary for different to select areas on the matching opposing surface for prepara-
situations. Consequently, the selection and location of speci- tionofthinsectionsandspecimensforoptical,chemical,X-ray
mens from the samples submitted for examination should be diffraction, or other examinations.
C856/C856M − 20
TABLE 1 Visual Examination of Concrete (1)
Coarse Aggregate + Fine Aggregate + Matrix + Air + Embedded Items
Composition:
A
Maximum dimension, mm or
in., in the range> d>
Type: Type: color, by comparison with more than 3 % of total, Type, size, location;
National Research kinds of metal; other
Council Rock Color items
Chart (1963)
1 Gravel 1 Natural sand predominantly in spherical
2 Crushed stone 2 Manufactured sand color distribution: voids?
3 Mixed 1 and 2 3 Mixed 1 mottled less than 3 % of total,
4 Other (name) 4 Other (name) 2 even abundant nonspherical
5 Mixed 1 + ⁄or 2 + ⁄or 4 5 Mixed 1 + ⁄or 2 + ⁄or 4 3 gradational changes voids?
If Type 1, 2, or 4, homogeneous If Type 1, 2, or 4, color differences between
or heterogeneous homogeneous or voids and mortar?
heterogeneous
Lithologic types voids empty, filled, lined, or
Coarse aggregate more than 20, partly filled
30, 40, or 50 % of total
Fabric:
Shape distribution shape voids below horizontal
distribution
Distribution distribution or low-angle
Packing grading (as perceptible) reinforcement
particle shape
Grading (even, uneven, parallelism of long axes of
as per-
ceptible
grading
preferred orientation
excess, or deficiency of irregular voids or sheets
size or sizes) of voids: with each other;
Parallelism of flat sides or with flat sides or long
long axes of exposed axes of coarse aggregate
sections, normal to
direction of placement
+ ⁄or parallel to formed and
B
finished surfaces
Condition: clean or corroded?
Does it ring when hit lightly with a hammer or give a dull flat sound? Can you break it with your fingers? Cracks? How distributed? Are cracks associated
Through or around coarse aggregate? With cores or sawed specimens, did the aggregate tear in drilling or sawing? Crack fillings? with embedded
Surface deposits? If air dry, are there unusually wet or dry looking areas? Rims on aggregate? items?
A
A substantial portion of the coarse aggregate has maximum dimensions in the range shown as measured on sawed or broken surfaces.
B
Sections sawed or drilled close to and parallel to formed surfaces appear to show local turbulence as a result of spading or rodding close to the form. Sections sawed
in the plane of bedding (normal to the direction of placement) are likely to have inconspicuous orientation. Sections broken normal to placement in conventionally placed
concrete with normal bond tend to have aggregate knobs abundant on the bottom of the upper piece as cast and sockets abundant on the top of the lower piece as cast.
10.1.4 Specimens obtained by diamond drilling are not 10.1.6 Heat used while impregnating concrete with thermo-
ordinarily damaged in the process; however, weak concrete plasticwaxorresinwillcausecrackingiftheconcreteisheated
damaged by chemical attack, an alkali–aggregate reaction, while it is wet, and will alter the optical properties of some
freezing and thawing, or several of these, will give poor core compounds, such as ettringite. Artifacts may therefore be
recovery with many fractures if it is drilled with a 54-mm produced and compound identification made difficult. These
[2 ⁄8-in.]orbitandbarrelwhileitwillgiveessentiallycomplete artifacts may be mistaken as original features. Care must
recovery if drilled with a 150-mm [6-in.] diameter bit and therefore be used in evaluating a particular feature and index-
barrel.This difference is particularly important in petrographic ing it as original in the specimen, or produced during the
examinations made during condition surveys of old structures. removal of the specimen from the structure or during labora-
Weakened concrete may also break during sawing. The re- tory processing.
moval and preparation of specimens for laboratory studies 10.1.7 When alkali–carbonate reactions are suspected and
usually involves the application of force and sometimes the rims around crushed carbonate aggregate are seen, it is useful
application of heat to the specimen. to etch a sawed or ground surface in 6 N or weaker hydrochlo-
10.1.5 The effects of force can be minimized during speci- ric acid to see if peripheral rims on coarse aggregate particles
men preparation by using thicker slices and making only one are more or less susceptible to etching than the interior of the
cut parallel to the long axis of a core section. Fractured or particle.Sinceetchingdestroysthesurface,thisstepshouldnot
fragile concrete can be supported by partially or completely be taken until all other examinations of the surface have been
encasing it in plaster, epoxy resin, or other reinforcing media completed. Etching the ground surface for 30 s in 10%
before sawing. hydrochloric acid is an appropriate procedure.
C856/C856M − 20
TABLE 2 Outline for Examination of Concrete with a Stereomicroscope (1)
NOTE 1—Condition—When it is examined at 6 to 10× under good light, the freshly broken surface of a concrete in good physical condition that still
A
retains most of its natural moisture content has a luster that in mineralogical terms is subtranslucent glimmering vitreous. Thin edges of splinters of the
paste transmit light; reflections appear to come from many minute points on the surface, and the quality of luster is like that from broken glass but less
intense. Concrete in less good physical condition is more opaque on a freshly broken surface, and the luster is dull, subvitreous going toward chalky.A
properlycuredlaboratoryspecimenfromaconcretemixtureofnormalproportionscured28daysthathasshownnormalcompressiveorflexuralstrength
and that is broken with a hammer and examined on a new break within a week of the time that it finished curing should provide an example of concrete
in good physical condition.
Under the same conditions of examination, when there is reasonable assurance that the concrete does not contain white portland cement or slag
cement,thecolorofthematrixofconcreteingoodphysicalconditionisdefinitelygrayordefinitelytan,exceptadjoiningoldcracksororiginalsurfaces.
Coarse Aggregate Fine Aggregate Matrix Voids
Lithologic types and mineralogy as percep- Lithologic types and miner- Color Grading
tible alogy as perceptible Fracture around or through aggregate Proportion of spherical to nonspherical
Surface texture Shape Contact of matrix with aggregate: Nonspherical, ellipsoidal, irregular, disk-
Within the piece: Surface texture close, no opening visible on sawed shaped
Grain shape Grading or broken surface; aggregate not Color change from interior surface to
Grain size extreme range observed, mm Distribution dislodged with fingers or probe; matrix
Median within range _ to _ mm boundary openings frequent, Interior surface luster like rest of ma-
Textureless (too fine to resolve) common, rare trix, dull, shining
Uniform or variable within the piece Width Linings in voids absent, rare, common,
From piece to piece: Empty in most, complete, partial, colorless,
Intergranular bond Filled colored, silky tufts, hexagonal tab-
B
Porosity and absorption Cracks present, absent, result of spec- lets, gel, other
If concrete breaks through aggregate, imen preparation, preceding spec- Underside voids or sheets of voids un-
through how much of what kind? imen preparation common, small, common, abundant
C
If boundary voids, along what kind of Supplementary Cementitious Materials
aggregate? All? All of one kind? More Contamination
than 50 % of one kind? Several kinds? Bleeding
Segregation
A
Dana, E. S., Textbook of Mineralogy, revised by W. E. Ford, John Wiley & Sons, New York, N. Y., 4th ed., 1932, pp. 273–274.
B
Pore visible to the naked eye, or at × _, or sucks in water that is dropped on it.
C
Darksolidspheresorhollow-centeredspheresofglass,orofmagnetite,orsomeofglassandsomeofmagnetite,recognizableatmagnificationof × 9onsawedorbroken
surfaces.Othermineraladmixtureswithcharacteristicparticlesvisibleatlowmagnificationarerecognizable.Groundsurfaceofconcretecontainingportlandblast-furnace
slag cement are unusually white near-free surfaces but retain greenish or blue-greenish patches, and slag particles can be seen with the stereomicroscope or polarizing
microscope.
10.2 Preparation of Immersion Mounts—Immersion mount refractive indices and other optical properties, specific identi-
samples are prepared for examinations using the petrographic
fications can be made of unknown compounds.
microscope. This type of examination provides versatility
10.2.4 Refractive index liquids available provide refractive
because materials can be immersed in liquids having different
index values to at least three decimal places (see 6.3.12).
refractive indices. Detailed knowledge of the use of the
Liquids accurate to two decimal places can be used if the
capabilities of the petrographic microscope is required to
petrographerisknowledgeableaboutBeckelinecolorsorother
properly examine immersion mounts.
techniques.
10.2.1 Immersion mounts are useful for observing and
identifying a variety of aggregate components, residual and 10.3 Preparation of Thin Sections—Thedetaileddescription
relict portland cement particles, the calcium hydroxide com-
ofthin-sectionpreparationisbeyondthescopeofthispractice.
ponent of cement hydration, components of blended cements,
There are many laboratories that provide this service if
supplementary cementitious materials, components resulting
in-house facilities are not available. The procedure includes
from chemical alteration of cementitious components and of 1
slicing the concrete into 2-mm [ ⁄16-in.] thick wafers if the
aggregates, secondary deposits from exposure of concrete to a
concrete is strong and thicker slices if it is not. It may be
variety of chemicals, and for confirming identifications by
necessarytoimpregnatetheconcretewitharesinbeforeslicing
other methods.
to prevent disintegration. Diluted flexibilized epoxy resins or
10.2.2 Powdersandfinechipsforimmersionmountscanbe
thermoplastic resins have been used successfully. The thin
prepared by: (1) pulverization of samples from which speci-
concrete slices are then mounted on glass slides with either
mens may be taken; (2) using a sharply pointed probe for
flexibilizedepoxy,Canadabalsam,orLakeside70,andground
removing specimens from small areas of aggregate and paste,
on laps using progressively finer abrasive until a thickness of
material in aggregate sockets, voids, and cracks; and (3)
30 µm or less is obtained; thickness not greater than 20 µm is
scrapings from fracture and formed surfaces.
required for detailed examination of the paste in transmitted
10.2.3 In immersion mounts, individual fragments are usu-
light. It is usually necessary to check the thickness of the
allyinrandomorientationsothattheidentificationofprincipal
sectionbytheuseofbirefringentcolorsofcommonmineralsin
refractiveindicesofamaterialcanbedeterminedinadditionto
the aggregate, such as quartz or feldspar, during the final
data about other optical characteristics. Portions of powdered
grinding stages. A cover glass is placed on the cleaned,
material, chips, or scraping are placed on a glass slide and
prepared section and secured with Canada balsam or other
immersed in an immersion liquid of known refractive index.A
cover slip is used on top of the preparation. Based upon media.
C856/C856M − 20
TABLE 3 Outline for Examination of Concrete in Thin Sections
Coarse and Fine Aggregate Relict Cement Grains and Hydration Products Characteristics of Cement Paste
Mineralogy, texture, fabric, variable or In concrete over two years old and normally cured, the Normal cement paste consists in plane transmitted
homogeneous. only residual cement grains are those that were light of pale tan matter varying somewhat in
Grading; excess or deficiency of sand sizes is to be largest, which may be composed of several index of refraction and containing relict
judged after examination of a series of thin constituents or be of alite or belite (substituted unhydrated cement grains. In concrete sectioned
sections. Grain size and nature of internal C S and C S). The latter two may be bordered at early age or not adequately cured, the paste
3 2
boundaries in aggregate. Classification of coarse by one or two layers of gel having different contains unhydrated cement grains ranging down
and fine aggregate. indexes of refraction, or by a layer of calcium to a few micrometres in maximum size with an
Natural mineral aggregate or crushed stone; natural hydroxide. The largest relict grains may be truly upper limit as large as 100 µm in maximum
or manufactured fine aggregate. unhydrated and retain the low (dark gray) diameter if the cement was ground in open-circuit
Bond with matrix; peripheral cracks inside the birefringence of alite in distorted quasihexagonal mills or was deliberately ground to low surface
borders of aggregate grains; internal cracks. sections and the visible birefringence to area to reduce the heat of hydration. With
General microfractures if one can establish that first-order yellow of the lamellar twins in rounded crossed polars, normal paste is black or very
they existed before thin-sectioning. grains of belite. Interstitial aluminoferrite appears dark mottled gray with scattered anhedral
Alkali - carbonate reactions—If the coarse as prismatic grains ranging in color from brown to poikilitic crystals or small segregations of calcium
aggregate is a carbonate rock or rocks, are there greenish brown to reddish brown and having a hydroxide and scattered relict grains of cement.
rims or partial rims depleted in calcium high refractive index and pleochroism masked by In concrete of high water–cement ratio and
hydroxide? Partly dolomitic rocks that have the color of the grain. Tricalcium aluminate is siliceous aggregate, the calcium hydroxide
reacted sometimes are bordered with paste free usually not recognized in thin section because the crystals are as large as the maximum size of
from calcium hydroxide along the dolomitic cubic form is isotropic or because it hydrates residual cement grains, about 100µ m. In
portion while the paste along the limestone early in the hydration history of the concrete concrete of lower water–cement ratio, higher
portion is normal. See other comments in forming submicroscopic ettringite or tetracalcium cement content, and either siliceous or carbonate
Column 3. aluminum sulfate hydrate or other tetracalcium aggregate, the maximum size of calcium
Alkali - silica reaction—Does the aggregate contain aluminum hydrates with or without other anions. hydroxide crystals is considerably smaller.
particles of types known to be reactive (chert, These may be visible in voids in older concrete Regardless of water–cement ratio and type of
novaculite, acid volcanic glass, cristobalite, but are best discriminated by X-ray diffraction. aggregate, calcium hydroxide crystals occupy
tridymite, opal, bottle glass)? If quartzite, Cements from different sources have different space tangential to the undersides of aggregate
metamorphosed subgraywacke, argillite, phyllite, colors of aluminoferrite and the calcium silicates particles. Where all the aggregate is carbonate
or any of those listed in the sentence above, are have pale green or yellow or white shades. It rock the maximum size of calcium hydroxide is
there internal cracks inside the periphery of the should be possible to match cements from one smaller than in comparable concrete with
aggregate? Has the aggregate been gelatinized source. siliceous aggregate. (Calcium hydroxide is
so that
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