A new Standard Reference Materialtextsuperscript® (SRM) for portland cement clinker has been prod... more A new Standard Reference Materialtextsuperscript® (SRM) for portland cement clinker has been produced for the Office of Standard Reference Materials at the National Institute of Standards and Technology (NIST). The SRM clinkers are intended for use in developing and testing quantitative methods of phase analysis for portland cement and cement clinker. The new SRM is one of three clinkers available from NIST representing the range of textures and compositions of North American clinker production. As the original SRM stock for SRM 2687 has been depleted, new material was obtained that retained the fine-grained texture of that SRM. Certification of the phase composition of the clinker is based upon consensus means and uncertainties of two independent analytical methods: scanning electron microscopy with image analysis and x-ray powder diffraction (XRD) analyses. The XRD data were subdivided to provide two separate sample sets processed separately using two different Rietveld refinement codes. These codes differed slightly in the determination of the silicate phases, which have very similar powder diffraction patterns and can be difficult to decompose. Therefore, the input data set for determining the consensus means, uncertainties and informational values is composed of two distinct XRD phase abundance estimates and one SEM/image analysis set of estimates. The XRD data are close to that determined by microscopy, but some distinct differences are seen. The disagreements may reflect the difficulty in resolving the fine-sized aluminate and ferrite interstitial phases using the microscope and challenges in decomposing highly overlapped powder diffraction data. The XRD data do display greater precision than replicate measurements by microscopy, likely the result of the specimen homogenization resulting from grinding the clinker to a powder. The certified reference values are consensus values, calculated by combining the results from both measurement techniques using the DerSimonian-Laird method with the standard uncertainties based upon the Horn-Horn-Duncan variance estimate. Reference values are best estimates based upon a single measurement technique. Reference values are provided for phases periclase, arcanite, aphthitalite, and lime and for the bulk oxides from x-ray fluorescence analysis.
In 1880, the Census Office and the National Museum in Washington, D.C., conducted a study of buil... more In 1880, the Census Office and the National Museum in Washington, D.C., conducted a study of building stones of the United States and collected a set of reference specimens from working quarries. The census that year reported descriptions of producing quarries, commercial building stones, and their use in construction across the country. This collection of stones, now augmented with the Centennial Collection of U.S. building stones from the 1876 Centennial Exhibition in Philadelphia, as well as building stones from other countries, has moved around over the years, but still serves its purpose as a stone test wall to study the effects of weathering.
The most frequently reported defect in ethylene-propylenediene terpolymer (EPDM) single-ply roofi... more The most frequently reported defect in ethylene-propylenediene terpolymer (EPDM) single-ply roofing systems is in fieldformed joints. The causes of these joint defects are largely unknown, but they tend to occur a short time after a roof is installed.
The ability to characterize the reactivity of fly ashes is an essential part of making use of thi... more The ability to characterize the reactivity of fly ashes is an essential part of making use of this aluminosilicate-rich waste product in geopolymer binders. Most fly ash reactivity investigations only consider the bulk reactivity of the ash because of incomplete information on the constituent phases. This study used a new method for characterizing fly ash and the resulting geopolymer reaction products that combines Rietveld quantitative x-ray diffraction (RQXRD) and scanning electron microscopy coupled with multispectral image analysis (SEM-MSIA) to quantitatively characterize both crystalline and glassy phases. The combined information from these methods gives quantitative mass fractions of each independent crystalline and glassy phase in any material analyzed, including unreacted fly ash, partially reacted fly ash, and geopolymer reaction products. The method was used in the present study for characterizing fly ashes prior to alkali-activation and to identify the reaction products formed in a geopolymer paste. The different phases in fly ash were shown to react differently in the alkaline environment required for geopolymerization. Originality Obtaining accurate, quantitative compositional information on the glassy phases in fly ash is essential in order to understand their behavior in geopolymer binders. The proposed characterization protocol is a novel way to determine this information using analytical equipment that is already used in cementitious materials analysis. The drawback of traditional fly ash chemical characterization by oxide analysis is the inability to identify and quantify individual glassy phases, not to mention to discern their different reactivities. By using this method to characterize the multiple glassy phases present in fly ash as opposed to assuming them to be uniform, a more targeted method for designing activating solutions can be developed.
The heat of hydration of hydraulic cements depends on a complex set of phase dissolution and prec... more The heat of hydration of hydraulic cements depends on a complex set of phase dissolution and precipitation reactions following the addition of water. Heat of hydration is currently measured in one of two ways: acid dissolution of the raw cement and a hydrated cement after 7 days or isothermal calorimetry. In principle, the heat of hydration should be predictable from knowledge of the cement composition and perhaps some measure of the cement fineness or total surface area. The improved mineralogical estimates provided by quantitative X-ray powder diffraction, together with improved statistical data exploration techniques that examine nonlinear combinations of candidate model constituents, were used to explore alternative predictive models for the 7-day heat of hydration. An exploratory tool, called “all possible alternating conditional expectations,” was created by combining all possible subsets regression with alternating conditional expectation to judiciously select variables within an explanatory variable class and subsets of variables across explanatory variable classes exhibiting the highest potential predictive power for additive nonlinear models for 7-day heat of hydration. Although a single, strong model for 7-day heat of hydration did not emerge from analyses, general conclusions were drawn. Good-fitting models included a key structural mineralogical phase (belite preferred); calcium sulfate phase (bassanite preferred); total fineness or surface area component (Blaine fineness preferred); and ferrite in conjunction with iron oxide, or aluminate, or cubic aluminate.
We report on the discovery of a new Gd 90 Co 2.5 Fe 7.5 alloy exhibiting superior magnetocaloric ... more We report on the discovery of a new Gd 90 Co 2.5 Fe 7.5 alloy exhibiting superior magnetocaloric properties compared to those of gadolinium. We present magnetically-derived entropy change, DS M , computed from magnetic data, and thermally-derived temperature change, DT ad , obtained from direct thermal measurements together with their respective MCE peaks for the alloy and gadolinium. The MCE peaks of the alloy are taller and broader than the corresponding MCE peaks of gadolinium. Correspondingly, the refrigeration capacity (RC) values of the alloy computed from magnetic and thermal MCEs for field changes, DH, of 400 kA/m (0.5 T) and 800 kA/m (1 T) are about 20% larger than those of gadolinium. Two possible mechanisms are proposed to account for the improved magnetocaloric properties of gadolinium alloyed with small amounts of Co and Fe, thereby pointing out a different methodology to use in the search for improved low field magnetic refrigerants.
The microstructure of mortars with water/solids ratios (w/s) of 0.36 and 0.29, cured under water ... more The microstructure of mortars with water/solids ratios (w/s) of 0.36 and 0.29, cured under water at 7, 23, and 40°C , were studied by scanning electron microscopy and X-ray powder dif fractometry. The mortars contained silica fume and a superplasticizer. The degree of hydration and extent of pozzolanic reaction was estimated after quantifying the residual unhydrated cement by image analysis and the mass percent calcium hydroxide by X-ray powder diffraction. Their microstructures were fairly homogeneous in both the bulk paste and at the paste-aggregate transition zone. In all mortars, the outer 250 /im was hydrated to about 85 percent and highly microcracked. The degree of hydration decreased rapidly beyond the outer zone to about 69 percent and less microcracking was observed. A temperature effect on the reactivity of silica fume was found.
The transformation of chemical analyses to phase estimates via the Bogue calculations has been su... more The transformation of chemical analyses to phase estimates via the Bogue calculations has been successfully used by industry for the past 70 years. Since its inception, however, it has been recognized as an estimate of potential phase composition based upon implicit assumptions that are neither correct nor complete. Other methodologies for the direct determination of phases in cements have been sought for potentially more accurate and more complete accounting of the actual phase composition of cements. Direct measurements of phase composition should provide a better basis for relating mineralogical composition to performance characteristics, and improving predictive capability for cements. Quantitative determination of cement phase composition has been performed by X-ray powder diffraction for over 50 years. These analyses required both careful preparation of calibration curves and measurement of the peak intensities from the resulting diffraction patterns. Difficulties encountered in these analyses include the matching of standards to the industrial phases due to the influences of chemical and structural variation on the phase patterns and measurement of diffraction peak intensities. Recent development of the Rietveld method for X-ray powder diffraction for multi-phase mixtures provides a means to overcome the difficulties of the earlier XRD analyses, resulting in a renewed interest in powder diffraction and a quantitative mineralogical tool. Statistical analyses of companion Bogue (ASTM C150) and quantitative X-ray powder diffraction (QXRD) estimates for cement phases are used to establish the most likely linear relationship between these two measurement techniques for alite, belite, aluminate, ferrite, and for the combinations (C 3 S+4.75•C 3 A) and (C 4 AF+2•C 3 A) used to characterize heat of hydration and sulfate resistance, respectively. This cross-calibration was performed using published data from more than 194 cements, spanning more than 50 years of manufacture. Each resulting calibration is a linear relationship, reported with 99 % Working-Hotelling-Scheffé confidence limits from the leastsquares regression. Fieller calibration intervals are used to report bounds for the QXRD values corresponding to the Bogue limits given in ASTM C150 Table 1. These bounds would allow either technique to be used for phase estimation to assess the compliance of a portland cement.
Serial sectioning is a technique of making and examining thin sections of material to obtain info... more Serial sectioning is a technique of making and examining thin sections of material to obtain information on three-dimensional structures from a series of two-dimensional images. Procedures were developed to make serial sections of hardened cement paste by the removal of thin layers by polishing. Backscattered electron imaging of the remaining paste block was used to record the paste microstructure after each section was removed. Procedures developed cover the polishing practice, the removal of thin layers by polishing, the estimation of layer thickness, and the location and alignment of specific regions for imaging.
A new Standard Reference Materialtextsuperscript® (SRM) for portland cement clinker has been prod... more A new Standard Reference Materialtextsuperscript® (SRM) for portland cement clinker has been produced for the Office of Standard Reference Materials at the National Institute of Standards and Technology (NIST). The SRM clinkers are intended for use in developing and testing quantitative methods of phase analysis for portland cement and cement clinker. The new SRM is one of three clinkers available from NIST representing the range of textures and compositions of North American clinker production. As the original SRM stock for SRM 2687 has been depleted, new material was obtained that retained the fine-grained texture of that SRM. Certification of the phase composition of the clinker is based upon consensus means and uncertainties of two independent analytical methods: scanning electron microscopy with image analysis and x-ray powder diffraction (XRD) analyses. The XRD data were subdivided to provide two separate sample sets processed separately using two different Rietveld refinement codes. These codes differed slightly in the determination of the silicate phases, which have very similar powder diffraction patterns and can be difficult to decompose. Therefore, the input data set for determining the consensus means, uncertainties and informational values is composed of two distinct XRD phase abundance estimates and one SEM/image analysis set of estimates. The XRD data are close to that determined by microscopy, but some distinct differences are seen. The disagreements may reflect the difficulty in resolving the fine-sized aluminate and ferrite interstitial phases using the microscope and challenges in decomposing highly overlapped powder diffraction data. The XRD data do display greater precision than replicate measurements by microscopy, likely the result of the specimen homogenization resulting from grinding the clinker to a powder. The certified reference values are consensus values, calculated by combining the results from both measurement techniques using the DerSimonian-Laird method with the standard uncertainties based upon the Horn-Horn-Duncan variance estimate. Reference values are best estimates based upon a single measurement technique. Reference values are provided for phases periclase, arcanite, aphthitalite, and lime and for the bulk oxides from x-ray fluorescence analysis.
In 1880, the Census Office and the National Museum in Washington, D.C., conducted a study of buil... more In 1880, the Census Office and the National Museum in Washington, D.C., conducted a study of building stones of the United States and collected a set of reference specimens from working quarries. The census that year reported descriptions of producing quarries, commercial building stones, and their use in construction across the country. This collection of stones, now augmented with the Centennial Collection of U.S. building stones from the 1876 Centennial Exhibition in Philadelphia, as well as building stones from other countries, has moved around over the years, but still serves its purpose as a stone test wall to study the effects of weathering.
The most frequently reported defect in ethylene-propylenediene terpolymer (EPDM) single-ply roofi... more The most frequently reported defect in ethylene-propylenediene terpolymer (EPDM) single-ply roofing systems is in fieldformed joints. The causes of these joint defects are largely unknown, but they tend to occur a short time after a roof is installed.
The ability to characterize the reactivity of fly ashes is an essential part of making use of thi... more The ability to characterize the reactivity of fly ashes is an essential part of making use of this aluminosilicate-rich waste product in geopolymer binders. Most fly ash reactivity investigations only consider the bulk reactivity of the ash because of incomplete information on the constituent phases. This study used a new method for characterizing fly ash and the resulting geopolymer reaction products that combines Rietveld quantitative x-ray diffraction (RQXRD) and scanning electron microscopy coupled with multispectral image analysis (SEM-MSIA) to quantitatively characterize both crystalline and glassy phases. The combined information from these methods gives quantitative mass fractions of each independent crystalline and glassy phase in any material analyzed, including unreacted fly ash, partially reacted fly ash, and geopolymer reaction products. The method was used in the present study for characterizing fly ashes prior to alkali-activation and to identify the reaction products formed in a geopolymer paste. The different phases in fly ash were shown to react differently in the alkaline environment required for geopolymerization. Originality Obtaining accurate, quantitative compositional information on the glassy phases in fly ash is essential in order to understand their behavior in geopolymer binders. The proposed characterization protocol is a novel way to determine this information using analytical equipment that is already used in cementitious materials analysis. The drawback of traditional fly ash chemical characterization by oxide analysis is the inability to identify and quantify individual glassy phases, not to mention to discern their different reactivities. By using this method to characterize the multiple glassy phases present in fly ash as opposed to assuming them to be uniform, a more targeted method for designing activating solutions can be developed.
The heat of hydration of hydraulic cements depends on a complex set of phase dissolution and prec... more The heat of hydration of hydraulic cements depends on a complex set of phase dissolution and precipitation reactions following the addition of water. Heat of hydration is currently measured in one of two ways: acid dissolution of the raw cement and a hydrated cement after 7 days or isothermal calorimetry. In principle, the heat of hydration should be predictable from knowledge of the cement composition and perhaps some measure of the cement fineness or total surface area. The improved mineralogical estimates provided by quantitative X-ray powder diffraction, together with improved statistical data exploration techniques that examine nonlinear combinations of candidate model constituents, were used to explore alternative predictive models for the 7-day heat of hydration. An exploratory tool, called “all possible alternating conditional expectations,” was created by combining all possible subsets regression with alternating conditional expectation to judiciously select variables within an explanatory variable class and subsets of variables across explanatory variable classes exhibiting the highest potential predictive power for additive nonlinear models for 7-day heat of hydration. Although a single, strong model for 7-day heat of hydration did not emerge from analyses, general conclusions were drawn. Good-fitting models included a key structural mineralogical phase (belite preferred); calcium sulfate phase (bassanite preferred); total fineness or surface area component (Blaine fineness preferred); and ferrite in conjunction with iron oxide, or aluminate, or cubic aluminate.
We report on the discovery of a new Gd 90 Co 2.5 Fe 7.5 alloy exhibiting superior magnetocaloric ... more We report on the discovery of a new Gd 90 Co 2.5 Fe 7.5 alloy exhibiting superior magnetocaloric properties compared to those of gadolinium. We present magnetically-derived entropy change, DS M , computed from magnetic data, and thermally-derived temperature change, DT ad , obtained from direct thermal measurements together with their respective MCE peaks for the alloy and gadolinium. The MCE peaks of the alloy are taller and broader than the corresponding MCE peaks of gadolinium. Correspondingly, the refrigeration capacity (RC) values of the alloy computed from magnetic and thermal MCEs for field changes, DH, of 400 kA/m (0.5 T) and 800 kA/m (1 T) are about 20% larger than those of gadolinium. Two possible mechanisms are proposed to account for the improved magnetocaloric properties of gadolinium alloyed with small amounts of Co and Fe, thereby pointing out a different methodology to use in the search for improved low field magnetic refrigerants.
The microstructure of mortars with water/solids ratios (w/s) of 0.36 and 0.29, cured under water ... more The microstructure of mortars with water/solids ratios (w/s) of 0.36 and 0.29, cured under water at 7, 23, and 40°C , were studied by scanning electron microscopy and X-ray powder dif fractometry. The mortars contained silica fume and a superplasticizer. The degree of hydration and extent of pozzolanic reaction was estimated after quantifying the residual unhydrated cement by image analysis and the mass percent calcium hydroxide by X-ray powder diffraction. Their microstructures were fairly homogeneous in both the bulk paste and at the paste-aggregate transition zone. In all mortars, the outer 250 /im was hydrated to about 85 percent and highly microcracked. The degree of hydration decreased rapidly beyond the outer zone to about 69 percent and less microcracking was observed. A temperature effect on the reactivity of silica fume was found.
The transformation of chemical analyses to phase estimates via the Bogue calculations has been su... more The transformation of chemical analyses to phase estimates via the Bogue calculations has been successfully used by industry for the past 70 years. Since its inception, however, it has been recognized as an estimate of potential phase composition based upon implicit assumptions that are neither correct nor complete. Other methodologies for the direct determination of phases in cements have been sought for potentially more accurate and more complete accounting of the actual phase composition of cements. Direct measurements of phase composition should provide a better basis for relating mineralogical composition to performance characteristics, and improving predictive capability for cements. Quantitative determination of cement phase composition has been performed by X-ray powder diffraction for over 50 years. These analyses required both careful preparation of calibration curves and measurement of the peak intensities from the resulting diffraction patterns. Difficulties encountered in these analyses include the matching of standards to the industrial phases due to the influences of chemical and structural variation on the phase patterns and measurement of diffraction peak intensities. Recent development of the Rietveld method for X-ray powder diffraction for multi-phase mixtures provides a means to overcome the difficulties of the earlier XRD analyses, resulting in a renewed interest in powder diffraction and a quantitative mineralogical tool. Statistical analyses of companion Bogue (ASTM C150) and quantitative X-ray powder diffraction (QXRD) estimates for cement phases are used to establish the most likely linear relationship between these two measurement techniques for alite, belite, aluminate, ferrite, and for the combinations (C 3 S+4.75•C 3 A) and (C 4 AF+2•C 3 A) used to characterize heat of hydration and sulfate resistance, respectively. This cross-calibration was performed using published data from more than 194 cements, spanning more than 50 years of manufacture. Each resulting calibration is a linear relationship, reported with 99 % Working-Hotelling-Scheffé confidence limits from the leastsquares regression. Fieller calibration intervals are used to report bounds for the QXRD values corresponding to the Bogue limits given in ASTM C150 Table 1. These bounds would allow either technique to be used for phase estimation to assess the compliance of a portland cement.
Serial sectioning is a technique of making and examining thin sections of material to obtain info... more Serial sectioning is a technique of making and examining thin sections of material to obtain information on three-dimensional structures from a series of two-dimensional images. Procedures were developed to make serial sections of hardened cement paste by the removal of thin layers by polishing. Backscattered electron imaging of the remaining paste block was used to record the paste microstructure after each section was removed. Procedures developed cover the polishing practice, the removal of thin layers by polishing, the estimation of layer thickness, and the location and alignment of specific regions for imaging.
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Papers by Paul Stutzman