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Abstract. Because the essential quality metrics of blast furnace slag are based on its oxide composition, the determination of chemical compositions of unh.
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Because the essential quality metrics of blast furnace slag are based on its oxide composition, the determination of chemical compositions of unhydrated slag grains in an aged concrete could be useful for understanding its past performance and in predicting the remaining service life of existing slag-bearing concrete. In the experimental study, seven concrete samples representing various service life durations were collected in the Netherlands. The microanalysis results of the samples revealed that the change in slag chemistry is insignificant for samples B to F ; however, elevated CaO and SiO 2 contents are found in slag used for sample G , opposite to that of Al 2 O 3 and MgO. After discussing compositional characterization, the paper discusses favorable microanalysis protocols for acceptable elemental quantification accuracy. It was concluded that quantitative EDS microanalysis is a strong tool to characterize the chemical composition of unhydrated slag used in field concrete, which could potentially contribute to understanding the correlations between composition and long-term performance in slag concrete structures. Since the early s, blast furnace slag henceforth slag cement has been used in a wide range of structural applications in regions such as Europe and North America Juenger et al. It should be noted that the chemical composition of slag has varied significantly over the decades according to the industrial reports Chesner et al. This change is likely due to, among other things, the use of iron-rich ore or pellet Chauhan, ; Li et al. Any changes in the composition of the burner or the furnace passage are expected to affect the composition of blast furnace slag produced. A better understanding of the chemical composition of slag grains in a well-performing aged concrete could be useful in designing and predicting the service life of modern slag-rich concrete. According to a group of professionals, while slag concrete produced in the past is still performing well, some of the new structures produced using comparable binders in the last decade have been showing performance issues just after a number of service years. Although there could be numerous reasons for the observed inferior performance, there is a consensus that the contemporary slag composition is likely to be the source of problems after discussion with industry experts. Because this claim is based purely on observations and experience, it needs scientific evidence to be considered valid which was the main motivation of this research. Therefore, the authors aimed to characterize unhydrated slag grains from different concrete structures representing different time periods, so that a snapshot of the compositional variation of slag during the past years could be identified. Attempts to obtain chemical compositions of slag used in older concrete are often unsuccessful possibly because the archives of QC reports are generally discarded after a number of years. Available bulk material analysis techniques, such as X-ray fluorescence spectrometry XRF and inductively coupled plasma-mass spectrometry ICP-MS —both of which are widely used for raw material characterization—are not the most favorable techniques for characterizing unhydrated slag grains due to high interference from other phases in concrete. On the other hand, energy-dispersive X-ray spectroscopy EDS stands out as a favorable technique as EDS allows semiquantitative and quantitative elemental analysis at a high spatial resolution. With this technique, characteristic X-rays released upon electron—solid interaction in a small volume captured, analyzed, and identified Reed, ; Goldstein, ; Goldstein et al. In this paper, the authors explore the feasibility of using EDS microanalysis as a tool for quantitative measurement of the chemical composition of unhydrated slag used in existing field concretes. Seven slag concrete samples were collected from randomly chosen locations in the Netherlands. A brief description of the samples is given in Table 1. Samples of different service life were investigated as the authors aimed to take a snapshot of the compositional variation of slags used in different periods during the past years. It should be noted that it is plausible to assume that the Portland cements clinkers that were blended together with slag did also show variations with respect to chemical composition and fineness. Table 1. To verify the accuracy of the standard-based method a. These five reference slags were synthesized in the laboratory with commercial slag provided by Ecocem Benelux B. Then, the molten liquid was water quenched to obtain the glassy slag. The slag to cement ratio was by mass and the water to binder ratio was 0. Bulk compositions of reference slags as determined by standard-based XRF are presented in Table 2. At the end of the curing, chemical compositions of these five reference slags were determined using quantitative standard-based and semiquantitative standardless EDS microanalysis on randomly selected unhydrated slag particles, and the results were compared with the original bulk slag composition that were detected by XRF correspondingly. For standardless EDS microanalysis, the results were generated using the internal standards of the X-ray microanalysis software. Table 2. Reference slag S2 and S3 with different MgO contents, and S4 and S5 with different Al 2 O 3 contents were chosen to be able to verify the standard-based method for different oxide levels, especially for minor constituents. Paste samples of approximately 6 mm in height were cut and immersed in isopropanol solution for 1 week to stop hydration. Once cured, the excess epoxy was removed from the sample surfaces by grinding and polishing operations; i. After each step, the samples were immersed briefly in an ultrasonic bath filled with Finally, the well-polished samples were carbon coated in a Leica EM CED carbon evaporator to a thickness of about 10 nm. All microanalysis was carried out at a working distance of 10 mm and an accelerating voltage of 10 kV, respectively. The take-off angle of the detector was During the analysis, an electron beam current of approximately 1. The X-ray collection time was set to 60 live-seconds per analysis in order to obtain acceptable statistics without introducing excessive thermal damage on the sample. Around 30 randomly chosen points per sample were investigated in order to increase the representability and reliability. Each point analysis was performed exclusively on an unhydrated slag particle. Monte Carlo simulation of the penetration of electrons accelerated at 10 kV into a hypothetical slag particle. Figure 1 illustrates the maximum penetration depth of electron trajectories, i. The lateral dimension was close to the depth of interaction volume assuming a 10 nm diameter beam Goldstein et al. Table 3. Because the current study focuses on four major elements, i. The basic routine for quantitative EDS microanalysis. A statistical summary of the EDS microanalysis of the reference slags S1 to S5 was computed and exported as shown in Table 4. The results include the mean value of each metal oxide and the standard deviation of the corresponding data set. The relatively large deviation and uncertainty of the amounts of the trace elements, among different methods see Table 5 , Ti, Mn, and S in particular, can be attributed to the following reasons: 1 EDS microanalysis is based on individual point or interaction volume, and it is different from XRF measurement which measures the bulk composition. Therefore, a minor fluctuation in noise can lead to a high relative deviation. Wavelength-dispersive X-ray spectrometry WDS can be recommended due to its relatively high spectral resolution, by a factor of ten or more, if the trace element is the main target for research. Table 4. Box plots of four main metal oxide contents of slag samples based on standard-based EDS microanalysis. The small hollow box indicates the mean value, the horizontal line inside the box the median, the lower and upper ends of the box the first and third quartile, respectively, and the two whiskers connected with the box by a vertical line indicate the minimum and maximum limits, and solid rhombus indicates the outliers. The results of sample A, which was dated back to s, display comparably large scatter reflected by the size of the box plot. Box plot of four main metal oxide contents of slag in field concrete samples as quantified by EDS microanalysis. Within a single slag particle, some elements showed an affinity for the small droplets of metallic iron. These elements were partitioned between the metallic and the glassy phases of slag, leading to the formation of heterogeneous slag grains with uneven element distribution Blotevogel et al. Moreover, higher amounts of metallic phases lead to lower glass contents due to the partitioning. In enriched slag grains with heavy metallic oxides such as TiO 2 and MnO, heterogeneity is more apparent Blotevogel et al. This phenomenon may increase the standard deviation of microanalysis results, therefore more analysis is needed to get a good estimate. Two large slag particles chosen from reference slag a S3 and b S5 pastes, respectively. Relying on the internal standards only leads to normalization of the detected composition, which could be highly erroneous for hydrated compounds. An evident difference was observed regarding the mass percentages of four main metal oxides in slag between standard-based and standardless microanalysis. Meanwhile, a much lower standard deviation is obtained for most metal oxides calculated from standard-based microanalysis. Outliers with extremely low or higher analytical total can be removed from the data set, which decreases the standard deviation considerably. Also, the analyst would be wise to further investigate the source of error, e. These pores in slag grain may result in errors on both excitation Z and absorption A corrections during quantitative microanalysis. Commonly, available rock-forming minerals do not resemble slag grain in terms of structure and composition. Thus, the selection of standards for each element of slag leads to variation in analytical total due to the matrix effect between the standard minerals and slag grain. Therefore, it is suggested that calibration studies should be carried out with available microanalysis standards in the future. The sulfur S in slag comes from iron pyrite used as raw material and coke for fuel. During quenching, it will be released in the form of H 2 S with water vapor and the residual sulfur can be found as sulfide in slag. However, the standard did not specify how to measure sulfide and sulfate contents in slag. During the quantitative EDS microanalysis, anhydrite was used as a microanalytical standard, and sulfate SO 3 was assumed to be the oxide form existing in slag, therefore in order to generate the oxide table, three oxygen atoms were assigned to one sulfur atom, stoichiometrically. This is the same for XRF analysis, both of which are based on X-ray characterization. However, the oxidation of any iron or manganese may influence the result. Based on the affinity to ion exchanger, this method can separate almost all charged ions Ninfa et al. Therefore, if sulfur content is the main concern of research, we recommend to combine these methods together and find the one or one of best availability. There is no specific requirement regarding the amount of TiO 2 in slag in EN However, a large relative deviation was found among different characterization methods. It is partially arising from the accelerating voltage of 10 kV employed here, and thus, a lower overvoltage ratio is obtained for Ti compared to other elements. In addition, it is challenging for concentration characterization as a trace element in slag. Therefore, WDS at higher accelerating voltage is recommended to determine the amount of TiO 2 in slag due to its relatively higher spectral resolution by a factor of ten or more, unless its heterogeneously distributed in the particles as trace constituent. Additionally, different blast furnace management and metallurgical technology may further change the composition of slag. All these reasons inevitably lead to variations of slag products throughout the world. Table 8 shows significant discrepancies with regards to the chemical composition of blast furnace slag examples in an international comparison. Table 8. Next to the geographical variations, slag compositions have been observed to vary in a single location over time, as reported in Ehgrenberg Our findings also revealed that an evident increase in CaO and SiO 2 contents is found in slag used for sample G Moreover, a survey on the recent publications — highlights a trend for consistent production of lime-rich and magnesium-poor slag in cement manufacturing, which appears to be especially distinct across Europe Alonso et al. The lime and magnesia in slag originate from the flux added into the blast furnace. The trend mentioned earlier indicates an increasing amount of limestone use over dolomite as the flux. No doubt this trend deserves more attention both from industry and academia. Therefore, related research should be performed when slag is used as a primary supplementary cementitious material SCM. This paper explored the potential to use EDS microanalysis as a tool for quantitative measurement of the chemical composition of unhydrated slag grains in existing concretes. Also, this is consistent with a recent trend has been observed that only lime-rich and low-magnesium slag is used for slag cement production. Similar research should be extended to other regions where slag is used as a primary SCM. For sulfur and titanium, a large relative deviation was found among different characterization methods when determining their concentrations, which was related to the heterogeneity of slag particle and oxidation state on sulfur. Therefore, a higher resolution technique such as WDS should be considered when these elements are of concern. Anna Alberda van Ekenstein and Bart Hendrix Microlab, TU Delft shared the samples collected from field for investigation, and authors would also like to thank them. ACI Slag Cement in Concrete and Mortar. ACI Committee Report. American Concrete Institute. Olive biomass ash as an alternative activator in geopolymer formation: A study of strength, radiology and leaching behaviour. Cement Concrete Compos , Google Scholar. Structure and Performance of Cements. London: CRC Press. Google Preview. MgO content of slag controls phase evolution and structural changes induced by accelerated carbonation in alkali-activated binders. Cem Concr Res 57 , 33 — Bijen J Benefits of slag and fly ash. Constr Build Mater 10 5 , — Ability of the R3 test to evaluate differences in early age reactivity of 16 industrial ground granulated blast furnace slags GGBS. Cem Concr Res , Effect of TiO 2 and 11 minor elements on the reactivity of ground-granulated blast-furnace slag in blended cements. J Am Ceram Soc 1 , — Parameters affecting the properties and microstructure of quicklime CaO -activated slag cement pastes. Cement Concrete Compos , — Chauhan DS Delft: TU Delft. User guidelines for waste and by-product materials in pavement construction. Recycled Materials Resource Center. Microanalysis of crystalline ASR products from a 50 year-old concrete structure. Crossin E The greenhouse gas implications of using ground granulated blast furnace slag as a cement substitute. J Cleaner Prod 95 , — Rheology, early-age hydration and microstructure of alkali-activated GGBFS-fly ash-limestone mixtures. Cem Concr Compos , Ehgrenberg A Huettensand: Ein leistungsfaehiger baustoff mit tradition und zukunft. Teile 1 und 2. Beton-Informationen 46 5 , 75— Granulated Blastfurnace Slag. Technical Leaflet No. The interpretation of energy-dispersive X-ray microanalyses from scanning electron microscopy, with some observations on CSH, AFm and AFt phase compositions. Cem Concr Res 33 9 , — FEhS Modification of cement pore fluid compositions by pozzolanic additives. Cem Concr Res 18 2 , — Goldstein J New York: Springer. Quantitative analysis: From k-ratio to composition. New York: Springer , pp. Hydration of alkali-activated slag: Comparison with ordinary Portland cement. Adv Cement Res 18 3 , — Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag—Part I: Effect of MgO. Cem Concr Res 41 9 , — Electron-optical analyses of the phases in a Portland cement clinker, with some observations on the calculation of quantitative phase composition. Cem Concr Res 15 5 , — Itoh T Rapid discrimination of the character of the water-cooled blast furnace slag used for Portland slag cement. J Mater Sci 39 , — Chloride-induced corrosion products of steel in cracked-concrete subjected to different loading conditions. Cem Concr Res 39 2 , — Jakobsen UH Microstructural surface deterioration of concrete exposed to seawater: Results after 2 years exposure. Effects of basicity and MgO in slag on the behaviors of smelting vanadium titanomagnetite in the direct reduction-electric furnace process. Metals 6 5 , Advances in alternative cementitious binders. Cem Concr Res 41 12 , — Effect of phosphonate addition on sodium carbonate activated slag properties. Microstructure and microchemistry of the paste-aggregate interfacial transition zone of high-performance concrete. Adv Cement Res 10 1 , 33 — Corros Sci 48 12 , — Structural role of titanium on slag properties. An innovative technique for comprehensive utilization of high aluminum iron ore via pre-reduced-smelting separation-alkaline leaching process: Part I: Pre-reduced-smelting separation to recover iron. Metals 10 1 , Environmental impact analysis of blast furnace slag applied to ordinary Portland cement production. J Cleaner Prod , — Cem Concr Res 42 2 , — Cem Concr Res 29 3 , — Zement 31 , — Scanning 35 3 , — J Mater Sci 50 2 , — Microsc Microanal 21 5 , — Anal Chem 67 11 , — Fundamental Laboratory Approaches for Biochemistry and Biotechnology. Utilization and efficiency of ground granulated blast furnace slag on concrete properties — A review. Constr Build Mater , — Quantitative energy-dispersive X-ray microanalysis of chlorine in cement paste. J Mater Civil Eng 28 1 , Optimisation of chloride quantification in cementitious mortars using energy-dispersive X-ray analysis. X-ray microanalysis of porous materials using Monte Carlo simulations. Scanning 33 3 , — Reed SJB New York: Cambridge University Press. Understanding the structure and structural effects on the properties of blast furnace slag BFS. ISIJ Int 59 7 , — Performance of concrete under accelerated physical salt attack and carbonation. Services ASM Metals 10 6 , Microanalysis of porous materials. Microsc Microanal 10 6 , — Taylor HF Cement Chemistry. London: Thomas Telford. Expansion of CEM I and slag-blended cement mortars exposed to combined chloride-sulphate environments. Effects of magnesium content and carbonation on the multiscale pore structure of alkali-activated slags. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign in through your institution. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents Abstract. Materials and Methodology. Journal Article. Yu Zhang , Yu Zhang. Corresponding author: Yu Zhang, E-mail: y. Oxford Academic. Karthikeyan Saravanakumar. Revision received:. Select Format Select format. Permissions Icon Permissions. Abstract Because the essential quality metrics of blast furnace slag are based on its oxide composition, the determination of chemical compositions of unhydrated slag grains in an aged concrete could be useful for understanding its past performance and in predicting the remaining service life of existing slag-bearing concrete. Open in new tab. A The sample was taken from a stairwell dating back to around Exact location was unknown. B The sample was collected from a wind deflection screen near Calandbrug, Europoort Rotterdam Port of Rotterdam , which was built in C The sample sourced from a parking garage built around It was located in Jupiterstraat, Hoofddorp. D The sample came from second Benelux tunnel in Vlaardingen, Rotterdam. E The sample was drilled from the beams above a tunnel in Delft, which was built in CaO Open in new tab Download slide. Target element. Figure 2 presents the essential steps in the quantitative EDS microanalysis routine from a to d. Subsequently, several points targeted at the unhydrated slag particles were chosen for electron bombardment as displayed in Figure 2b. It should be noted that the points were chosen close to the grain center on the relatively large particles, in order to avoid interference from the surrounding matrix. Figure 2c displays a typical EDS microanalysis spectrum of an unhydrated slag grain in b. It contains seven main X-ray peaks as labeled; the carbon C signal is mainly due to the carbon coating. Here, the user-defined threshold minimum energy cutoff was set to eV in order to include oxygen O which is present in all EDS spectra In this paper, we quantified oxygen stoichiometrically. The peaks from unknown spectra were quantified using a k -ratio fitting routine with the known compositions of standards spectra. A typical residual spectrum was rendered in Figure 2d. We assumed that the analysis was completed with acceptable accuracy, as no unassigned minor peak was left, and the residual count was sufficiently low. Table 5. RD1 a. RD2 a. CaO 1. Figure 3 shows a box plot based on the quantitative microanalysis results of the four main metal oxide contents in the reference slag samples. Each plot corresponds to a single metal oxide mass percentage. Results showed that a few points fell outside the box and the whisker ends, which indicates sporadic compositional imperfections. On the other hand, the slender boxes do imply a relatively homogeneous composition. Upon verifying the suitability of the microanalysis standards on the reference samples, the same methodology was applied on the field concrete specimens. The oxide compositions of the unhydrated slag grains were determined and listed in Table 6 and the statistical variation of the main oxides is summarized in Figure 4. Furthermore, the microanalysis results lead to the following observations: 1 The results of sample A, which was dated back to s, display comparably large scatter reflected by the size of the box plot. Table 6. Five reference slags S1 to S5 were almost entirely amorphous based on X-ray diffraction characterization with low amounts of heavy metal oxides, e. Therefore, significant heterogeneity was not expected in these slag grains. The homogeneity of slag grains was then evaluated with EDS point analysis for confirmation. Two relatively large slag particles were selected from S3 and S5 reference slag pastes, respectively, on which around ten spot analysis points were chosen as shown in Figure 5. A statistical summary of the chemical compositions regarding the four main metal oxide contents is shown in Table 7. Compared with the results displayed in Table 4 , the standard deviation of points within a single slag grain decreases significantly, and the extremely low coefficient of variation Table 7 further proves that these two slags were highly homogeneous, and there was negligible heterogeneity. Table 7. Netherlands This paper. Australia Services, Google Scholar Crossref. Search ADS. Le Cornec. For commercial re-use, please contact journals. Issue Section:. Download all slides. Views More metrics information. Total Views Email alerts Article activity alert. Advance article alerts. New issue alert. Receive exclusive offers and updates from Oxford Academic. Citing articles via Web of Science 3. More from Oxford Academic. Biological Sciences. Science and Mathematics. Authoring Open access Purchasing Institutional account management Rights and permissions. Get help with access Accessibility Contact us Advertising Media enquiries. The sample was collected from a wind deflection screen near Calandbrug, Europoort Rotterdam Port of Rotterdam , which was built in The sample sourced from a parking garage built around The sample came from second Benelux tunnel in Vlaardingen, Rotterdam. The sample was drilled from the beams above a tunnel in Delft, which was built in
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