1、Designation: C1723 10Standard Guide forExamination of Hardened Concrete Using Scanning ElectronMicroscopy1This standard is issued under the fixed designation C1723; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides information for the examination ofhardened concrete using scanning electron microscopy (SEM)combined wit
3、h energy-dispersive X-ray spectroscopy (EDX).Since the 1960s, SEM has been used for the examination ofconcrete and has proved to be an insightful tool for themicrostructural analysis of concrete and its components. Thereare no standardized procedures for the SEM analysis ofconcrete. SEM supplements
4、techniques of light microscopy,which are described in Practice C856, and, when applicable,techniques described in Practice C856 should be consulted forSEM analysis. For further study, see the bibliography at the endof this guide.This guide is intended to provide a general introduction tothe applicat
5、ion of SEM/EDS analytical techniques for theexamination and analysis of concrete. It is meant to be usefulto engineers and scientists who want to study concrete and whoare familiar with, but not expert in, the operation and applica-tion of SEM/EDS technology. The guide is not intended toprovide expl
6、icit instructions concerning the operation of thistechnology or interpretation of information obtained throughSEM/EDS.It is critical that petrographer or operator or both be familiarwith the SEM/EDX equipment, specimen preparation proce-dures, and the use of other appropriate procedures for thispurp
7、ose. This guide does not discuss data interpretation. Properdata interpretation is best done by individuals knowledgeableabout the significance and limitations of SEM/EDX and thematerials being evaluated.1.2 The SEM provides images that can range in scale froma low magnification (for example, 153) t
8、o a high magnifica-tion (for example, 50 0003 or greater) of concrete specimenssuch as fragments, polished surfaces, or powders. Theseimages can provide information indicating compositional ortopographical variations in the observed specimen. The EDXsystem can be used to qualitatively or quantitativ
9、ely determinethe elemental composition of very small volumes intersectingthe surface of the observed specimen (for example, 1-10 cubicmicrons) and those measured compositional determinationscan be correlated with specific features observed in the SEMimage. See Note 1.NOTE 1An electronic document con
10、sisting of electron micrographsand EDX spectra illustrating the materials, reaction products, and phe-nomena discussed below is available at http:/netfiles.uiuc.edu/dlange/www/CML/index.html.1.3 Performance of SEM and EDX analyses on hardenedconcrete specimens can, in some cases, present unique chal
11、-lenges not normally encountered with other materials analyzedusing the same techniques.1.4 This guide can be used to assist a concrete petrographerin performing or interpreting SEM and EDX analyses in amanner that maximizes the usefulness of these techniques inconducting petrographic examinations o
12、f concrete and othercementitious materials, such as mortar and stucco. For a morein-depth, comprehensive tutorial on scanning electron micros-copy or the petrographic examination of concrete and concrete-related materials, the reader is directed to the additionalpublications referenced in the biblio
13、graphy section of thisguide.1.5 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with the use of electronmicroscopes, X-ray spectrom
14、eters, chemicals, and equipmentused to prepare samples for electron microscopy. 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
15、:2C125 Terminology Relating to Concrete and Concrete Ag-gregatesC294 Descriptive Nomenclature for Constituents of Con-crete Aggregates1This practice is under the jurisdiction of ASTM Committee C09 on Concreteand ConcreteAggregates and is the direct responsibility of Subcommittee C09.65 onPetrography
16、.Current edition approved Oct. 1, 2010. Published November 2010.2For 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 page onthe ASTM websi
17、te.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.C295 Guide for Petrographic Examination of Aggregatesfor ConcreteC457 Test Method for Microscopical Determination ofParameters of the Air-Void System in Hardened ConcreteC856 Practic
18、e for Petrographic Examination of HardenedConcreteC1356 Test Method for Quantitative Determination ofPhases in Portland Cement Clinker by MicroscopicalPoint-Count Procedure3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 BSE, nbackscatter electrons; these are high-energyelectro
19、ns emitted back from the specimen surface. Elements ofhigher atomic number will have stronger emissions and appearbrighter.3.1.2 brightness, nthe amount of energy used to producean X-ray.3.1.3 charging, nthe buildup of electrons on the specimenat the point where the beam impacts the sample. Charging
20、 canalter the normal contrast of the image (usually becomesbrighter) and may deflect the beam. Coating the specimen witha thin layer of conductive material (such as gold or carbon) canminimize this effect.3.1.4 contrast, nthe difference in intensity of the energyproduced by varying elements when exc
21、ited.3.1.5 dead-time, nthe time of finite processing duringwhich the circuit is “dead” and unable to accept a new pulsefrom the X-rays.3.1.6 EDX (energy-dispersive X-ray spectroscopy), ntheinteraction of the electron beam with atoms in the sampleproduces characteristic X-rays having energies and wav
22、e-lengths unique to atoms.3.1.7 live-time, nhow the acquistion of X-ray data istimed when the rate of X-ray events between measurements arecompared. Opposite of dead-time.3.1.8 K, L, or M peaks, ncharacteristic X-ray intensitiesdetected for elements.3.1.9 raster, nto scan as when the beam from the f
23、ilamentsweeps back and forth over the sample3.1.10 SE, nsecondary electrons; these are low-energyelectrons emitted when the specimen is hit with the beam andassociated with the topography of the same.3.1.11 SEM, nscanning electron microscope.3.1.12 stage, nplatform upon which the specimen isplaced w
24、ithin the vacuum chamber that can be remotely movedin various directions.3.1.13 working distance, nthe distance between the de-tector and the sample. Each SEM will have an optimundistance in which X-rays can be collected for EDX.3.1.14 X-ray detector, nalso known as EDX system.4. Description of Equi
25、pment4.1 The principles of the electron system of the scanningelectron microscope, the interactions of the electron beam andthe specimen under examination, and the detection systemsused for the examination are based on concepts that needunderstanding if the resulting image and other analyticalinform
26、ation obtained are to be best resolved and understood.An abbreviated discussion is provided here. A more compre-hensive understanding can be obtained from texts devoted tothis subject (1,2).34.1.1 SEM Optics4.1.1.1 An electron beam is generated in a column consist-ing of an electron gun and multiple
27、 electromagnetic lenses andapertures. The electron beam is generated by heating a filamentso that it emits electrons. The most common filament forgeneral SEM work is tungsten, but other filaments can be usedfor increased brightness. The electrons are accelerated towardsthe specimen by an applied pot
28、ential and then focused bylenses and apertures. The energy of the electron beam influ-ences resolution, image quality, and quantitative and qualita-tive X-ray microanalyses.4.1.1.2 The electron beam is finely focused through electro-magnetic lenses and apertures. A smaller beam size improvesresoluti
29、on, but decreases signal intensity.4.1.1.3 Electron systems operate under vacuum. Specimensshould be prepared to minimize alteration or damage whenthey are exposed to the vacuum (See 5.1.3). Variable pressurescanning electron microscopes, low vacuum scanning electronmicroscopes (LVSEM), and environm
30、ental scanning electronmicroscopes (ESEM) permit the examination of samples con-taining some moisture under low vacuum. The ESEM alsoallows analysis of organic materials. Even in an ESEM,however, some drying occurs.4.1.2 Signal Generation and Detection4.1.2.1 The interaction of the electron beam wit
31、h the samplegenerates several types of signals that can be utilized forimaging and X-ray microanalysis. The intensities of thesesignals are measured by detectors. The signals allow theexamination and determination of properties such as surfacetopography, elemental composition, and spatial distributi
32、on ofcomponents. Signal intensities are generally used to provide animage on a screen.4.1.2.2 The signals that are produced when the electronbeam strikes the specimen surface are secondary electrons(SE), backscattered electrons (BSE), and X-rays.4.1.2.3 To generate an image, the electron beam is mov
33、edrepeatedly across the specimen to form a raster. The magnifi-cation is the ratio between the size of the raster and that of thescreen image.4.1.2.4 Images produced by secondary electrons are mostcommonly utilized for topographical imaging. The SE intensitydepends mainly on the angles between the e
34、lectron beam andthe specimen surface and between the specimen surface and thedetector. The SE intensity is relatively insensitive to thespecimen composition.4.1.2.5 Images produced by backscattered electrons areoften used for elemental contrast imaging. The BSE image isuseful for identifying differe
35、nt chemical constituents in con-crete. The BSE intensity depends on the average atomicnumber and density of each phase. The BSE intensity alsodepends on the angles between the electron beam and thespecimen surface and between the specimen surface and the3The boldface numbers in parentheses refer to
36、a list of references at the end ofthis standard.C1723 102detector. Therefore, some BSE detectors can be manipulated toobserve the sample topography.4.1.2.6 The interaction of the electron beam with atoms inthe sample produces characteristic X-rays having energies andwavelengths unique to atoms. Chem
37、ical analysis (or mi-croanalysis) is performed using an X-ray spectrometer thatmeasures the energies and intensities of the X-rays. Theintensities of X-rays depend upon many factors, includingelectron beam currents and accelerating voltages, as well aschemical composition of the specimen interacting
38、 with theelectron beam.4.1.2.7 One important parameter for image quality is theworking distance, the distance between specimen surface andthe point where the electron beam exits the electron optics.Small working distances maximize BSE collection efficiencyand improve the image resolution. Long worki
39、ng distancesimprove image depth of field for topographical images butdecrease image resolution. The working distance generallymust be within a predetermined range to perform X-raymicroanalysis.5. Materials and Features5.1 Important microstructural features include the size andshape of individual con
40、stituents (including pores), the spatialrelationships between these constituents (what constituents aretouching or associated with each other), and the volumefraction of each constituent. Constituents are described in moredetail by Taylor (3).In order to study these microstructural features, it is n
41、eces-sary to recognize the individual phases which are usuallyrecognized by their size, shape, association, backscatter inten-sity and elemental composition (See Note 1 for examples).These characteristics may sometimes be insufficient to conclu-sively identify a phase, or to differentiate between tw
42、o phases,such as chert and quartz (See Terminology C125). In this case,other techniques must be used, such as XRD or polarizing lightmicroscopy. Additional information can be found in PracticeC856.5.1.1 ConcreteHardened concrete consists of aggregate,hydration products of pozzolanic and cementitious
43、 materials,residual cement particles, capillary pores and voids. Someconcrete may also contain supplementary cementitious mate-rials, organic, inorganic, and metallic fibers, and entrained airvoids.5.1.2 Cement PasteThe cement paste contains residualcement, frequently supplementary pozzolanic and ce
44、mentitiousmaterials, and various hydration products that together have acomplex and porous microstructure. The paste is initially amixture of individual grains of cementious materials and water,and may also contain chemical admixtures. Over time, hydra-tion reactions consume the cement and produce v
45、arious hydra-tion products, some of which grow on the surface of cementgrains, while progressively filling the initial water-filled space.5.1.2.1 Residual portland cement particles appear dense andangular to subangular.Alite usually has at least one crystal facewhile belite is usually rounded and so
46、metimes striated. In aBSE image, residual portland cement particles occur as rela-tively bright objects in a matrix of gray cement hydrationproducts.5.1.2.2 Calcium-silicate-hydrate is the major hydrationproduct of portland cement and is usually amorphous or verypoorly crystalline. Its morphology va
47、ries depending on thecalcium to silica ratio, water to cementitious materials ratio,curing conditions, degree of cement hydration, and chemicaladmixtures. At high magnifications, the morphology ofcalcium-silicate-hydrate varies from very fine fibrous growths,to sheet-like units, to irregular massive
48、 grains.5.1.2.3 Portlandite (calcium hydroxide) is a major phase ofcement hydration and occurs in variable sizes and shapesincluding platy hexagonal crystals and sheet-like masses,depending on the orientation. Calcium hydroxide is normallyobserved throughout the cement paste and sometimes developsal
49、ong paste-aggregate interfaces. It also sometimes occurs assecondary deposits in voids and cracks.5.1.2.4 Ettringite is a primary product of the reactionsbetween calcium aluminates and the sulfate phases in cement.It has a characteristic acicular shape. Ettringite often alsoappears as a secondary deposit. Secondary deposits of ettring-ite are commonly found in voids and cracks. X-ray microanaly-sis is sometimes required for its identification. A compoundthat has similar morphology is thaumasite (See 5.1.6 onsecondary deposits). These two compounds can be distin-guis
