bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure of Cement Blends Containing Fly Ash, Silica Fume, Slag and Fillers
Authors: Regourd Micheline 
Published: March 2011

ABSTRACTThe hydration of a blended cement through hydraulic or pozzolanic reactions results in heterogeneous polyphase materials. Because portland cement clinker is the major component in most cement blends, the microstructural development of portland cement hydrates, including C-S-H and pore structures, is first discussed. Slag, fly ash, silica fume and limestone filler cements are then compared to portland cement with regards to C-S-H morphology and composition, aluminate crystallization, cement paste interfaces and pore size distribution.
The Role of Sodium Hydroxide in the System C3A-CaSO4-H2O at 30°C
Authors: Ghorab Hanaa Youssef , Fetouh Safaa Hussein Abou El 
Published: March 2011

ABSTRACTThe hydration reaction of C3A with gypsum (molar ratio = 1:1.5) has been studied in water and in sodium hydroxide solutions at 30°C. The hydration product were analyzed microscopically and by means of X-ray diffraction. The concentration of sulfate and aluminum in solution was determined spectrophotometrically. In the absence of alkali, the amount of ettringite formed passes through a maximum and is accompanied by almost complete consumption of sulphate ion in solution. Alkali depresses the formation of ettringite and accelerates that of calcium hydroxide. The monosulfate hydrate appears immediately in alkaline solutions and water then reappears after a day as a solid solution with the tetracalcium aluminate hydrate. The formation of the monophase solid solution is accompanied by the consumption of C3A, ettringite, and calcium hydroxide and by an increase in the amount of the dissolved aluminum. The presence of alkali markedly increases the initial sulfate ion concentration from solution.
Homogeneity of Particle Dispersion in Slag/Cement Blends and its Effect on Hydration Rate
Authors: Lee S. , Roy D. M. , Malek R. I. A. 
Published: March 2011

ABSTRACTEffective particle dispersion is believed to play a significant role in hydration reactivity of slag/cement blends and consequently on the development of physical and mechanical properties of the hardened pastes. The effects of various factors (superplasticizer and mixing time) on the particle dispersion were evaluated using a computer controlled scanning electron microscope. Backscattered electron signals and elemental maps were resolved for polished mounts of slag and cement particle mixtures. The adequacy of dispersion of slag and cement particles was determined by analyzing about 1000 particles per analysis with appropriate calculations and statistical treatment. These results were related to the hydration behavior of the slag/cement blends. The results obtained can be used to evaluate some of the physical phenomena and the kinetics of slag-cement hydration.
Relationships Among Retardation, Expansion, Microstructure, and Phase Composition for a Salt-Saturated Expansive Grout
Authors: Wakeley Lillian D. 
Published: March 2011

ABSTRACTA salt-saturated and sulfate-expansive grout was formulated with four levels of sodium citrate to determine effects on workability and setting time. Linear expansion of restrained grout prisms increased with amount of citrate used, apparently a function of extent of retardation of the grouts. This relationship was observed both for grouts cured for at least 53 days, and for a concrete formulated from the same cementitious materials cured for at least 180 days age.The microstructures of the grouts at 28 days age showed notable increases in extent of reaction of the sulfate phases and in formation of ettringite with increasing citrate content, and thus with increasing retardation of set. XRD also revealed an increase in well-crystallized ettringite and decrease in gypsum with greater retardation. These observations provide a microstructural and compositional link between retardation and expansion of cementitious materials formulated to be expansive.
Towards Computer-Based Microstructure Models for Cement-Based Systems
Authors: Jennings Hamlin M. 
Published: March 2011

ABSTRACTComputer-based models represent an important development that should provide a scientific basis for in-depth predictions of the behavior of materials. Aspects of microstructure models for cement-based systems are described. A computer model is described that can incorporate many assumptions in the form of sub-models. Specific algorithms are selected to solve specific parts of the problem. The algorithm chosen depends on specific problem requirements at each stage of calculation, and these problem requirements may not be anticipated in advance. An important part of these computer models is that they incorporate a file of numbers, representing the microstructure, which can be operated on to effect an incremental change in the system.
Effect of Particle Size Distribution on Hydration Kinetics
Authors: Pommersheim James M. 
Published: March 2011

ABSTRACTA general method has been developed for determining the effects of particle size distribution (PSD) on the kinetics of hydration. Given the PSD and the kinetic rate for particles having a single size, expressions can be derived for the variation of the total degree of hydration with time. The method was applied to PSD and kinetic functions typical of cement systems that account for reaction, diffusion and expansion of spherical hydrate layers. The PSD was found to critically affect the kinetics. A key feature of the theory follows with time those particles that have become totally hydrated, so-called “dead” particles. This produces a dead-particle hydration curve having approximately the same shape and location as the overall hydration curve. It can be represented analytically in all cases and gives a measure of the disguise provided by the distribution.
The Reactivity of C109 Sand: A Closer Look
Authors: Grutzeck Michael W. 
Published: March 2011

ABSTRACTIt was observed that standard ASTM C 109 sand (St. Peter Sandstone) from working quarries in the Ottawa area (northeastern Illinois) is nearly always sub-angular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications the frosted surface of the quartz sand was found to consist of a thin layer of micron-sized, coprecipitated quartz crystals and occasional kaolinite flakes. Upon reaction of the sand with either a saturated Ca(OH)2 solution or as part of a sand-cement paste, some of these features were preserved, whereas others were lost. Micrographs of sand cured in cement paste at 90°C are presented showing that the kaolinite flakes react and become “puffy” and rounded in appearance. Also, the smooth surfaces of the large, terminated quartz overgrowths are severely etched as a result of dissolution. Sand reacted at 38°C in saturated Ca(OH)2 solution demonstrated more subtle effects, perhaps obscured by precipitated CaCO3 and C-S-H on the surfaces of the quartz overgrowths. These results suggest that ASTM C 109 sand is not entirely inert, but exhibits a limited amount of temperature-dependent pozzolanic activity.
Pore Structure Development in Portland Cement/Fly Ash Blends
Authors: Cook David J. , Cao Huu T. , Coan Everett P. 
Published: March 2011

ABSTRACTPore structure development in portland cement/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally >0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.
Comparison of the Behavior of Trace Elements During Acid Leaching of Ashes from Several Coals
Authors: Watson J. S. 
Published: March 2011

ABSTRACTThe leaching of fly ash from eastern U.S. coals with strong mineral acid is the initial step in a series of potential processes for producing useful and marketable materials from the ash. This initial leaching step removes most, or all, of the more soluble (generally amorphous) materials from the ash and leaves an inert residue, believed to be mostly mullite and silica. Chemical analyses of the leachate and the residual inert materials indicate the original distribution of the trace elements in the phases. Significant differences in crystallography, composition and leaching behavior have been noted in ash samples from coals from various regions, of various types, and sometimes even in ash samples from the same or similar coals. Trace element analyses of fly ash leachates provide a useful means of studying coal characteristics and of determining how the trace elements are incorporated in various types of fly ashes.
Status of ASTM and Other National Standards for the Use of Fly Ash Pozzolans in Concrete
Authors: Majko Richard M. 
Published: March 2011

ABSTRACTThe Subcommittee of ASTM that is responsible for pozzolan specifications, (C09.03.10) is currently revising C 618, the standard specification, and C 311, the standard test methods. It is no small task. It is generally considered that dividing fly ashes into two classifications (Class F and Class C) is no longer acceptable. The Subcommittee has reached the tentative conclusion that one class of fly ash pozzolan is more appropriate and less ambiguous, provided it is accompanied by an optional table outlining the appropriate limits for sulfate resistance, heat of hydration, hydraulic properties, etc. That is, the engineer need specify only a fly ash pozzolan. If the engineer needs more than a “general purpose” fly ash he calls for special characteristics from the optional requirement table. Any major revision in the C 618 specification challenges the Subcommittee to look for better and more useful test methods in C 311. The committee is looking at C 1012 for a sulfate resistance procedure, conduction calorimetry as a heat of hydration method, and better methods to evaluate pozzolanic activity. The committee is aware of the limited usefulness of hydrated lime or sodium hydroxide in evaluating pozzolanic activity. Perhaps a more suitable term, i.e. the activity index with cement, is more appropriate. Fly ash properties that need to be evaluated include water reduction, activation by lime and alkalies, hydraulic or self-cementing properties and pozzolanic activity. Any test that tends to compensate for a fly ash's lower reactivity (i.e., accelerated thermal curing at 35°C or 65°C) probably leads to misleading results. A critical look at the national standards of other countries might allow the committee to take a visionary yet practical approach toward a new fly ash specification.
Studies of Zinc, Cadmium and Mercury Stabilization in OPC/PFA Mixtures
Authors: Poon C. S. , Perry R. 
Published: March 2011

ABSTRACTThe utilization of pulverized fuel ash (PFA) (fly ash) for the stabilization of heavy metal waste is described. Solutions of the group IIB elements (zinc, cadmium and mercury) are used as model materials because of their significance as industrial wastes. The study included aqueous chemistry determinations, a leaching test, the use of SEM to examine microstructure, and compressive strength measurements. The use of PFA in a cementitious matrix lowers the alkalinity of the overall system and thus improves the immobilization of the amphoteric metal such as zinc. The interaction between mercuric solution and PFA plays an important role in improving the retention of the blended system for mercury. SEM results show that the microstructure of the ordinary Portland cement (OPC)/PFA blended system is significantly modified by the incorporation of the waste material. The advantages of using the blended system over a pure OPC system are described in physical and chemical terms.
SEM Study of Chemical Variations in Western U.S. Fly Ash
Authors: Tevenson Robert J. , Huber Timothy P. 
Published: March 2011

ABSTRACTScanning electron microscope/electron microprobe chemical analyses of individual grains of several western fly ashes have shown an inter-grain variation in composition for ashes derived from both lignite and subbituminous western coals. SRM 2689 (a Class F fly ash from a bituminous coal) and SRM 2691 (a Class C fly ash from a subbituminous coal) have been included in the study and also show inter-grain chemical variation. A classification scheme of fly ash grain compositions has been developed and has proven to be useful in illustrating the differences and similarities of the ashes. There is a positive correlation, for example, between grains rich in SiO2 and Al2O3 and the Na2O content of the grains in lignite and subbituminous coal derived fly ashes. There is also a positive correlation between grains rich in CaO and the MgO content of the grains in both classes of fly ashes.
Microgravity Materials Processing for Commercial Applications
Authors: Kohli R. , Brusky P. L. , Diamond S. , Markworth A. J. , McGinniss V. D. , Melling P. J. , Spinosa E. D. , Collings E. W. 
Published: March 2011

AbstractMaterials processing in a microgravity environment is aimed at developing commercial materials as well as investigating basic phenomena to improve earth-based processing. Materials research in space has dealt with glasses and ceramics, crystal growth, electronic materials, metals and alloys, polymers, composites, and biological materials. Battelle has been conducting research in this area since the early-1970s. Several important results have been obtained in: immiscible alloys, containerless under-cooling of clustering alloys, sol-gel glasses, and collagen fibers.More recently, Battelle's Advanced Materials Center for the Commercial Development of Space (CCDS) has been established to utilize the microgravity environment in the commercial development of composite and mixed-phase materials with substantially improved properties. Currently, the Center is conducting research in catalysts (variant-phase chlorides, zeolites, and mixed oxides), polymer systems, electronic materials (float-zone crystal growth on Type II-VI semiconductor crystals, particularly CdTe), and con-trolled- porosity glass. The present program focuses on a proof of principle for each research thrust, utilizing ground-based and suborbital facilities, together with modeling to demonstrate the potential for producing commercially important materials.Each of these research programs is outlined. In addition, the more important developments in each of the major categories of microgravity materials research is reviewed.
Containerless Polymeric Microsphere Production for Biomedical Applications
Authors: Rhim W. K. , Hyson M. T. , Chung S. K. , Colvin M. , Chang M. 
Published: March 2011

AbstractA containerless method that produces highly uniform microspheres (> 50 microns in diameter) from many materials has been developed for biomedical applications. A piezoelectrically vibrated drop generator forms uniform (monodisperse) monomer droplets that are either electrostatically levitated and polymerized using UV irradiation, or free radical polymerized. Spheres of 2-hydroxyethyl methacrylate (HEMA) polymer have been produced with diameters of 155 microns ±1.57%.
PbO Reduction and Crucible Reactions of 70 wt% PbO · 30 wt% B2O3 Glass
Authors: Schilling Christopher H. , Lee Mark C. 
Published: March 2011

AbstractSeventy wt% PbO · 30 wt% B2O3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.
Experimental Studies in Fluid Mechanics and Materials Science Using Acoustic Levitation
Authors: Trinh E. H. , Robey J. , Arce A. , Gaspar M. 
Published: March 2011

AbstractGround-based and short-duration low gravity experiments have been carried out with the use of ultrasonic levitators to study the dynamics of freely suspended liquid drops under the influence of predominantly capillary and acoustic radiation forces. Some of the effects of the levitating field on the shape as well as the fluid flow fields within the drop have been determined. The development and refinement of measurement techniques using levitated drops with size on the order of 2mm in diameter have yielded methods having direct application to experiments in microgravity. In addition, containerless melting, undercooling, and freezing of organic materials as well as low melting metals have provided experimental data and observation on the application of acoustic positioning techniques to materials studies.
Viscosity Temperature Dependence and Crystallization of Heavy Metal Fluoride Classes
Authors: CrichtoN S. N. , Mossadegh R. , Moynihan C. T. , Gupta P. K. , Drexhage M. G. 
Published: March 2011

ABSTRACTThe temperature dependence of the viscosity of heavy metal fluoride glasses is important for determining processing temperatures for procedures such as fiber drawing and in understanding crystallization behavior in these systems. Viscosity data in the glass transition region and in the liquid region have been measured by several different laboratories for ZBLA (58 ZrF4-33 BaF2-5 LaF3-4 AlF3) and ZBLAN viscosity-temperature curves for these two compositions are highly non-Arrhenius in nature, and cannot be described by the Fulcher equation; however the Cohen-Crest equation fits the data very well. On a reduced temperature scale (Tg/T), the viscosity curves nearly coincide, suggesting the possibility of a master viscosity equation for fluorozicronate glasses. Crystallization temperatures for these compositions have been measured by differential scanning calorimetry. On reheating, the first crystallization product for both compositions is a barium fluorozicronate phase. However, ZBLAN glass does not crystallize until a much lower viscosity is reached, compared to ZBLA. These results indicate that the devitrification behavior for ZBLAN is due to additional entropy of mixing from the addition of NaF.
Strength of Ge-Sb-Se Chalcogenide Glass Fibers
Authors: Swiler Daniel R. , Varshneya Arun K. , Prideaux Peter H. 
Published: March 2011

ABSTRACTStrength of Ge-Sb-Se UV-cured acrylate coated chalcogenide glass fibers was measured in various environments using specially designed fixtures for testing in tensile and bending modes. The data are analyzed using Weibull statistics. Humid or water immersion initially lowered the observed strength of these fibers, presumably due to corrosion by the moisture which penetrated the semi-porous coating. However, after the glass surface became wetted, there was no evidence of further strength degradation (over 1.5 months of immersion).
Optical Spectra of Silica Core Optical Fibers Exposed to Hydrogen
Authors: Lemaire P. J. , Decoteau M. D. 
Published: March 2011

ABSTRACTThe reaction of H2 with undoped silica core fibers was evaluated by means of “in situ” spectral loss measurements. Drawing induced loss peaks at 0.63 μm decreased rapidly upon exposure to hydrogen. Simultaneous loss increases at 1.39 and 1.53 μm suggest that H2 reacts at nonbridging oxygens and oxygen vacancies created during the drawing process, forming SiOH and SiH. The 1.53 μm SiH peak slowly decayed after its initially rapid growth, indicating that SiH is not thermodynamically stable in silica. The concentration of drawing induced defects is estimated to be on the order of 100 ppb, based on the time required for H2 to diffuse to the fiber core. The appearance of peaks at 1.45 μm suggests that HF is formed by reaction of H2 in the fluorine doped cladding of the fibers.
Fluorine Doping of Pyrogenic Silica
Authors: Miller T. J. , Nicol D. A. , Pohl K. D. , Clark H. R. 
Published: March 2011

ABSTRACTThe incorporation of atomic fluorine into flame synthesized silica boules has been investigated. Soot boules were doped with fluorine using three different methods: (A) in a low temperature process, using XeF2 as the fluorinating agent prior to consolidation, (B) utilizing SiF4 or SF6 in the reagent gas mix during the combustion synthesis and soot deposition step and (C) in situ treatment with SF6 during the dehydration/ consolidation step at elevated temperatures. All three methods produced uniformly down-doped glass after consolidation, although the maximum fluorine incorporation and level of down-doping for each method followed A <B <C. Fluorine incorporation mechanisms are proposed for each method.
Magnetic Specific Heat of Cd1−xMnxTe at Low Temperatures and High Magnetic Fields
Authors: Ching W. Y. , Huber D. L. 
Published: March 2011

AbstractTheoretical predictions for the magnetic specific heat of Cd1−xMnxTe:x=0.20, 0.35, 0.50, and 0.65 are reported for B=0, 10T, and 100T. The analysis applies to the low-temperature regime, T≤10K, where the fundamental excitations are harmonic magnons. The calculations use values for the exchange interactions which were inferred from fits to the dynamic structure factor describing inelastic neutron scattering at low temperatures. For x=0.35, 0.50, and 0.65 the specific heat is only weakly affected by applied fields up to 10T. At the lowest concentration the application of a field of 10T leads to a significant reduction in the specific heat. Results are also presented for the distribution of magnon modes at various concentrations and fields.
Development of Electrostatic Levitator at JPL
Authors: Rhim Won-Kyu , Saffren Melvin M. , Elleman Daniel D. 
Published: March 2011

ABSTRACTWe report preliminary results of the design and operation of electrostatic levitators we have developed at JPL. Discussion is focussed on the single-axis levitators for groundbased operation and for operation in the reduced gravity environment. Design principles and the performance of final products are described.
Air Jet Levitation Furnace System for Observing Glass Microspheres During Heating and Melting
Authors: Ethridge Edwin C. , Dunn Stanley L. 
Published: March 2011

ABSTRACTA collimated hole structure air jet levitation system has been developed which can be used to levitate hollow glass microspheres used in inertial confinement fusion studies. An ellipsoidal furnace has been added to the system to provide a heating source. A video camera and a 16 mm movie camera connected to a microsphere system provide real time observation as well as permanent documentation of the experiments. Microspheres have been levitated at temperatures over 1400°C for over 10 minutes at a time.