1、Designation: C1723 10C1723 16Standard 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 o
2、f last revision. 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 of hardened concrete using scanning electron microscopy (SEM)com
3、bined with energy-dispersive X-ray spectroscopy (EDX). (EDX or EDS). Since the 1960s, SEM has been used for theexamination of concrete and has proved to be an insightful tool for the microstructural analysis of concrete and its components.There are no standardized procedures for the SEM analysis of
4、concrete. SEM supplements techniques of light microscopy, whichare described in Practice C856, and, when applicable, techniques described in Practice C856 should be consulted for SEM analysis.For further study, see the bibliography at the end of this guide.This guide is intended to provide a general
5、 introduction to the application of SEM/EDS analytical techniques for the examinationand analysis of concrete. It is meant to be useful to engineers and scientists who want to study concrete and who are familiar with,but not expert in, the operation and application of SEM/EDS technology. The guide i
6、s not intended to provide explicit instructionsconcerning the operation of this technology or interpretation of information obtained through SEM/EDS.It is critical that petrographer or operator or both be familiar with the SEM/EDX equipment, specimen preparation procedures,and the use of other appro
7、priate procedures for this purpose. This guide does not discuss data interpretation. Proper datainterpretation is best done by individuals knowledgeable about the significance and limitations of SEM/EDX and the materialsbeing evaluated.1.2 This guide is intended to provide a general introduction to
8、the application of SEM/EDS analytical techniques for theexamination and analysis of concrete. It is meant to be useful to engineers and scientists who want to study concrete and who arefamiliar with, but not expert in, the operation and application of SEM/EDS technology. The guide is not intended to
9、 provideexplicit instructions concerning the operation of this technology or interpretation of information obtained through SEM/EDS.1.3 It is critical that petrographer or operator or both be familiar with the SEM/EDX (EDS) equipment, specimen preparationprocedures, and the use of other appropriate
10、procedures for this purpose. This guide does not discuss data interpretation. Properdata interpretation is best done by individuals knowledgeable about the significance and limitations of SEM/EDX (EDS) and thematerials being evaluated.1.4 The SEM provides images that can range in scale from a low ma
11、gnification (for example, 15) to a high magnification (forexample, 50 000 or greater) of concrete specimens such as fragments, polished surfaces, or powders. These images can provideinformation indicating compositional or topographical variations in the observed specimen. The EDX (EDS) system can be
12、 usedto qualitatively or quantitatively determine the elemental composition of very small volumes intersecting the surface of theobserved specimen (for example, 1-10 cubic microns) and those measured compositional determinations can be correlated withspecific features observed in the SEM image. See
13、Note 1.NOTE 1An electronic document consisting of electron micrographs and EDX (EDS) spectra illustrating the materials, reaction products, andphenomena discussed below is available at http:/netfiles.uiuc.edu/dlange/www/CML/index.html.1.5 Performance of SEM and EDX (EDS) analyses on hardened concret
14、e specimens can, in some cases, present uniquechallenges not normally encountered with other materials analyzed using the same techniques.1.6 This guide can be used to assist a concrete petrographer in performing or interpreting SEM and EDX (EDS) analyses in amanner that maximizes the usefulness of
15、these techniques in conducting petrographic examinations of concrete and othercementitious materials, such as mortar and stucco. For a more in-depth, comprehensive tutorial on scanning electron microscopy1 This guide is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates
16、 and is the direct responsibility of Subcommittee C09.65 onPetrography.Current edition approved Oct. 1, 2010Sept. 1, 2016. Published November 2010October 2016. Originally approved in 2010. Last previous edition approved in 2010 asC1723 10. DOI: 10.1520/C1723-10.10.1520/C1723-16.This document is not
17、an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate.
18、 In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1or the petrographic examination of concrete and concrete-related mate
19、rials, the reader is directed to the additional publicationsreferenced in the bibliography section of this guide.1.7 UnitsThe values stated in SI units are to be regarded as standard. No other units of measurement are included in thisstandard.1.8 This standard does not purport to address all of the
20、safety concerns, if any, associated with the use of electron microscopes,X-ray spectrometers, chemicals, and equipment used to prepare samples for electron microscopy. It is the responsibility of the userof this standard to establish appropriate safety and health practices and determine the applicab
21、ility of regulatory limitations priorto use.2. Referenced Documents2.1 ASTM Standards:2C125 Terminology Relating to Concrete and Concrete AggregatesC294 Descriptive Nomenclature for Constituents of Concrete AggregatesC295 Guide for Petrographic Examination of Aggregates for ConcreteC457 Test Method
22、for Microscopical Determination of Parameters of the Air-Void System in Hardened ConcreteC856 Practice for Petrographic Examination of Hardened ConcreteC1356 Test Method for Quantitative Determination of Phases in Portland Cement Clinker by Microscopical Point-CountProcedure3. Terminology3.1 Definit
23、ions of Terms Specific to This Standard:3.1.1 BSE, nbackscatter electrons; these are high-energy electrons emitted back from the specimen surface. Elements ofhigher atomic number will have stronger emissions and appear brighter.3.1.2 brightness, nthe amount of energy used to produce an X-ray.3.1.3 c
24、harging, nthe buildup of electrons on the specimen at the point where the beam impacts the sample. Charging can alterthe normal contrast of the image (usually becomes brighter) and may deflect the beam. Coating the specimen with a thin layer ofconductive material (such as gold or carbon) can minimiz
25、e this effect.3.1.4 contrast, nthe difference in intensity of the energy produced by varying elements when excited.3.1.5 dead-time, nthe time of finite processing during which the circuit is “dead” and unable to accept a new pulse from theX-rays.3.1.6 EDX (EDS) (energy-dispersive X-ray spectroscopy)
26、, nthe interaction of the electron beam with atoms in the sampleproduces characteristic X-rays having energies and wavelengths unique to atoms.3.1.7 live-time, nhow the acquistion of X-ray data is timed when the rate of X-ray events between measurements arecompared. Opposite of dead-time.3.1.8 K, L,
27、 or M peaks, ncharacteristic X-ray intensities detected for elements.3.1.9 raster, nto scan as when the beam from the filament sweeps back and forth over the sample3.1.10 SE, nsecondary electrons; these are low-energy electrons emitted when the specimen is hit with the beam andassociated with the to
28、pography of the same.3.1.11 SEM, nscanning electron microscope.3.1.12 stage, nplatform upon which the specimen is placed within the vacuum chamber that can be remotely moved in variousdirections.3.1.13 working distance, nthe distance between the detector and the sample. Each SEM will have an optimun
29、 distance inwhich X-rays can be collected for EDX.EDX (EDS).3.1.14 X-ray detector, nalso known as EDX (EDS) system.4. Description of Equipment4.1 The principles of the electron system of the scanning electron microscope, the interactions of the electron beam and thespecimen under examination, and th
30、e detection systems used for the examination are based on concepts that need understandingif the resulting image and other analytical information obtained are to be best resolved and understood.An abbreviated discussionis provided here. A more comprehensive understanding can be obtained from texts d
31、evoted to this subject (1,2).32 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The boldface numbers in paren
32、theses refer to a list of references at the end of this standard.C1723 1624.1.1 SEM Optics:4.1.1.1 An electron beam is generated in a column consisting of an electron gun and multiple electromagnetic lenses andapertures. The electron beam is generated by heating a filament so that it emits electrons
33、. The most common filament for generalSEM work is tungsten, but other filaments can be used for increased brightness.The electrons are accelerated towards the specimenby an applied potential and then focused by lenses and apertures. The energy of the electron beam influences resolution, imagequality
34、, and quantitative and qualitative X-ray microanalyses.4.1.1.2 The electron beam is finely focused through electromagnetic lenses and apertures. A smaller beam size improvesresolution, but decreases signal intensity.4.1.1.3 Electron systems operate under vacuum. Specimens should be prepared to minim
35、ize alteration or damage when they areexposed to the vacuum (See 5.1.35.1.4). Variable pressure scanning electron microscopes, low vacuum scanning electronmicroscopes (LVSEM), and environmental scanning electron microscopes (ESEM) permit the examination of samples containingsome moisture under low v
36、acuum. The ESEM also allows analysis of organic materials. Even in an ESEM, however, some dryingoccurs.4.1.2 Signal Generation and Detection:4.1.2.1 The interaction of the electron beam with the sample generates several types of signals that can be utilized for imagingand X-ray microanalysis. The in
37、tensities of these signals are measured by detectors. The signals allow the examination anddetermination of properties such as surface topography, elemental composition, and spatial distribution of components. Signalintensities are generally used to provide an image on a screen.4.1.2.2 The signals t
38、hat are produced when the electron beam 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 moved repeatedly across the specimen to form a raster. The magnificationis the ratio between the size of the
39、raster and that of the screen image.4.1.2.4 Images produced by secondary electrons are most commonly utilized for topographical imaging. The SE intensitydepends mainly on the angles between the electron beam and the specimen surface and between the specimen surface and thedetector. The SE intensity
40、is relatively insensitive to the specimen composition.4.1.2.5 Images produced by backscattered electrons are often used for elemental contrast imaging. The BSE image is useful foridentifying different chemical constituents in concrete. The BSE intensity depends on the average atomic number and densi
41、ty ofeach phase. The BSE intensity also depends on the angles between the electron beam and the specimen surface and between thespecimen surface and the detector. Therefore, some BSE detectors can be manipulated to observe the sample topography.4.1.2.6 The interaction of the electron beam with atoms
42、 in the sample produces characteristic X-rays having energies andwavelengths unique to atoms. Chemical analysis (or microanalysis) is performed using an X-ray spectrometer that measures theenergies and intensities of the X-rays. The intensities of X-rays depend upon many factors, including electron
43、beam currents andaccelerating voltages, as well as chemical composition of the specimen interacting with the electron beam.4.1.2.7 One important parameter for image quality is the working distance, the distance between specimen surface and the pointwhere the electron beam exits the electron optics.
44、Small working distances maximize BSE collection efficiency and improve theimage resolution. Long working distances improve image depth of field for topographical images but decrease image resolution.The working distance generally must be within a predetermined range to perform X-ray microanalysis.5.
45、 Materials and Features5.1 Important microstructural features include the size and shape of individual constituents (including pores), the spatialrelationships between these constituents (what constituents are touching or associated with each other), and the volume fractionof each constituent. Const
46、ituents are described in more detail by Taylor (3).In order to study these microstructural features, it is necessary to recognize the individual phases which are usually recognizedby their size, shape, association, backscatter intensity and elemental composition (See Note 1 for examples). These char
47、acteristicsmay sometimes be insufficient to conclusively identify a phase, or to differentiate between two phases, such as chert and quartz(See Terminology C125). In this case, other techniques must be used, such as XRD or polarizing light microscopy. Additionalinformation can be found in Practice C
48、856.5.1.1 In order to study these microstructural features, it is necessary to recognize the individual phases which are usuallyrecognized by their size, shape, association, backscatter intensity and elemental composition (See Note 1 for examples). Thesecharacteristics may sometimes be insufficient
49、to conclusively identify a phase, or to differentiate between two phases, such as chertand quartz (See Terminology C125). In this case, other techniques must be used, such as XRD or polarizing light microscopy.Additional information can be found in Practice C856.5.1.2 ConcreteHardened concrete consists of aggregate, hydration products of pozzolanic and cementitious materials, residualcement particles, capillary pores and voids. Some concrete may also contain supplementary cementitious materials, organic,inorganic, and metallic fibers, and entrained air voids.5.
