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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Neutron and X-Ray Scattering Studies of New Green Cement, and Nanoconfined Water

This is the Final report on DE-FG02-90ER45429 for the time period from September 1, 1990 to May 31, 2017. The Principal Investigator is Sow-Hsin Chen, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139 (email: sowhsin@mit.edu). The Administrative Point of Contact at MIT is Sarah Svenson, Senior Contract Administrator, Office of Sponsored Programs, Tel: 617-253-2495, ssvenson@mit.edu. The DOE Program is the Office of Basic Energy Sciences (BES); Program manager is Dr. P. Thiyagarajan, Neutron Scattering SC-22.2/, Germantown Bldg., Germantown, MD 20874 . During these 27 years, the scientific activities has had a number developing emphases, as reflected from the change of Project Title in 1990 as “Construction of a Small Angle Neutron Scattering Spectrometer for Investigation of Microemulsions and Micellar Solutions in Bulk, in Porous Materials...” to “Neutron and X-Ray Scattering Studies of New Green Cement, and Nanoconfined Water” in the last renewal period, 2015-2017, with many title changes in between. Progress Report for each sub-project period was reported to DOE with detailed activity and budgetary reports. It is fair to summary that the chief activity has been in the use neutron, x-ray and laser spectroscopy to investigate materials properties of complex fluids and soft condensed matter. It started with conducting neutron and X-ray scattering experiments to study the structure and dynamics of glass-forming liquids in general first, then more specifically in the case of supercooled water in confined geometry, and culminating in the final study of new green cement. Experiments were conducted at various DOE supported national neutron facilities including ORNL, ANL, BNL and Los Alamos, as well as at NIST/NCNR. Whenever possible, experiments were also performed at numerous world-class facilities, such as those at Saclay and the Institut Laue Langevin (ILL) in Grenoble, France, and at National Synchrotron Radiation Research Center (NSRRC) in recent years in Taiwan, etc. Leveraging on the large number of international collaborate activities, a substantial percentage of activities were supported with collaborators’ own funding sources. These have help to carry out DOE’s mission and produce impressive research products far beyond what was possible with only DOE funding supports. The chief product during this period, 1990-2017, includes (1) Three hundred and eight scientific articles published in peer-reviewed and high-impacted scientific journals during 1990-2017, and a dozen monographs including four books for scientists and graduate students, (2) Twenty-four scientific conferences organized and 209 papers presented at many national and international conferences, (3) educate and train 9 post-doctoral fellows and 28 students including 22 Ph.D. students, 3 M.S. students, and 3 in other categories by providing a research experience in neutron and X-Ray scattering techniques, most of them were supported wholly or in part in the scientific topic of this award during the funding period and (4) numerous high-visibility awards and honors. This final report summarizes and details these research activities and products. At the close of this funding period, the fund from DOE has been totally spent.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2024

Alternative Pozzolans for Replacement of Fly Ash in Grout: Literature Review for Continuous Improvement of Cement Waste Forms

The Department of Energy (DOE) is currently responsible for treating radioactive and mixed waste, performing environmental restoration, and closing contaminated tanks and facilities resulting from nuclear weapons production during the Cold War. Cementitious reagents are the most widely used materials for (1) chemically stabilizing and encapsulating radionuclides and hazardous metals and (2) solidifying radioactive wastewater. Cementitious grouts and flowable concretes are also the most widely used materials for tank and facility closures and are used extensively for physical as well as chemical stabilization in environmental restoration projects. Ambient temperature radioactive waste cementation is a widely used technology for producing waste forms for final disposal. The current practice of designing and testing waste forms is based on a mid to late 20th century technology approach (i.e., materials, characterization, and test methods) for generating parameters for risk assessments. DOE technology development is needed to address both current, long-term, and emerging issues in this area as new waste streams come online and as regulations, performance knowledge, and risk assessment methodology continue to evolve. Consequently, the use of cementation as a means of treating chemically challenging radioactive liquid waste streams and reactive debris requires an enduring effort.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Castable Cement Can Prevent Molten-Salt Corrosion in CSP

NREL's study demonstrated that castable cements on metals are a protective barrier that can prevent permeation of molten salts toward metallic surfaces. The silica-based castable cement Aremco 645-N, when sprayed with boron nitride, can protect containment metallic alloys from attack by molten chlorides at high temperatures (650 degrees C) in short-term tests. Improved thermal energy storage technology could increase the performance of CSP and reduce costs, helping to reach the goal of the U.S. Department of Energy's SunShot Initiative to make solar cost-competitive with other non-renewable sources of electricity by 2020.

14 SOLAR ENERGY↗
DOE OSTI2017

Bandwidth Study on Energy Use and Potential Energy Savings Opportunities in U.S. Cement Manufacturing

Energy bandwidth studies can serve as foundational references in framing the range (or bandwidth) of potential energy savings opportunities in U.S. manufacturing. This bandwidth study examines energy consumption and potential energy savings opportunities in U.S. cement manufacturing. The study relies on multiple sources to estimate the energy used in the production of four cement manufacturing sub-processes, representing 97% of sector-wide energy consumption in 2010. Energy savings opportunities for the sub-processes are based on technologies currently in use or under development; these potential savings are then extrapolated to estimate sector-wide energy savings opportunity.

energy energy bandwidth study, cement, advanced ma↗
DOE OSTI2015

An Ice Block: A Novel Technique of Successful Prevention of Cement Leakage Using an Ice Ball

We report three cases of painful bone metastases with extraosseous invasion treated with cementoplasty and cryoablation. Due to significant cortical loss in all cases, the ice ball was used simultaneously during cementoplasty to deter potential cement leakage. This was achieved by direct application of the ice ball against the cortical surface, resulting in adequate consolidation and successful containment of the cement within the treated bones. To the authors’ knowledge, this is the first report to describe such a combined technique.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Control of Carbon Content in Ultrafine Cemented Carbide by Heat Treatment in Reducing Atmospheres Containing Carbon Oxides

In this work, the method of control of carbon content in the ultrafine-grained cemented carbide alloy was proposed. The treating of the WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} compacts was made in a CO + CO{sub 2} gas mixture at CO concentrations from 0 to 80 vol.% during 50 min at the initial stage of the conventional sintering at a temperature of 700 °C. Conditions for increasing and decreasing the carbon content are CO concentrations of CO in gas mix more than 65 vol.% and less than 35 vol.%, respectively. It is shown that even a small deviation from the stoichiometric carbon content (0.3 wt.%) leads to an increase in porosity and a multiple decrease in the strength of the ultrafine-grained cemented carbide. A comparative analysis with literature data showed that the obtained ultrafine-grained solid alloy WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} with stoichiometric composition is not inferior in hardness and toughness to the analogs obtained by hot pressing and electrospark sintering.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Porous structure and mechanical strength of cement-lime pastes during setting

The acceleration of a cement paste setting as a result of lime addition may be shown from isothermal calorimetry measurements. We investigated the underlying mechanisms through two techniques that provide information on porous structure (using Nuclear Magnetic Resonance) and mechanical properties (elastic modulus measured by rheometry). The correlation of the two sets of results on a cement paste clearly reveals the successive steps of setting, and particularly highlights the so-called induction period. We show that this induction period disappears in the presence of lime, leading to an acceleration of the setting. We also show that beyond some critical concentration of added lime the acceleration of setting is negligible.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of environmental exposure on autogenous self-healing of cracked cement-based materials

Despite abundant literature on self-healing of cement-based materials, there is dearth of information on how environmental exposure affects self-healing. In this study, self-healing of cracks in cement mortar under different environmental exposure was investigated. Pre-cracked mortar specimens were submerged in water, while identical specimens were exposed to cyclic temperature and relative humidity. Change in crack width was examined using optical microscopy. SEM coupled with energy dispersive X-ray analysis was used to identify healing compounds. Mercury Intrusion Porosimetry, water absorption and permeability were employed to assess porosity. X-ray computed tomography was deployed to explore healing of internal cracks. No significant self-healing occurred in specimens exposed to cyclic T and RH. Although crack self-healing was identified in submerged specimens, X-ray μCT demonstrated that it was limited to exposed surface of specimens. This warrants further research to bridge the gap between laboratory findings on self-healing and actual field performance of ageing civil infrastructure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Modeling of aqueous species interaction energies prior to nucleation in cement-based gel systems

Arguably the most ubiquitous construction material in modern civilization, concrete is enabling the development of megacities around the globe together with increasing living standards in developing nations. However, the exact formation mechanisms of the strength-giving calcium-rich gels remain a topic of debate. Using density functional modeling, we simulate the fundamental solution-based building blocks of cement hydrates (calcium ions and silicate and aluminate monomers) and their propensity to form pair-wise complexes with bonding environments characteristic of those found in calcium-silicate-hydrate, calcium-alumino-silicate-hydrate and sodium-containing calcium-alumino-silicate-hydrate gels, as assessed from Gibbs free energies of chemical reactions. By accurately simulating the high pH pore solution chemistry in Portland cements and related systems, along with discrete solvation of the species, we hypothesize potential early age formation routes of the gels and discuss limitations and future work associated with this approach.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermal conductivity of cement paste: Influence of macro-porosity

Thermal conductivity of cement paste is significantly influenced by the presence of macro-pores within it. These pores (pores with size greater than 6 μm, measured using microCT) which may be filled with air and/or water significantly alters the thermal conductivity of the resulting material. A combination of experiments, molecular dynamic investigations of major constituents of the cement paste, multiscale homogenization techniques, and inclusion of thermal conductivity of the pores containing either air or water has been utilized in this study to reveal the influence of pores in the calculation of thermal conductivity of the composite material.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Physical and chemical effects of isopropanol exchange in cement-based materials

Drying cement-based materials is a necessary step to characterize the microstructure by microscopy, adsorption, or mercury intrusion. The isopropanol (IPA) exchange method is commonly used to replace the pore solution prior to drying, as it reduces the capillary pressure and thereby helps to preserve the microstructure of the hydrated cementitious materials. However, some physical and chemical effects of IPA on hydration products have been reported. These effects cannot be completely avoided, but can be reduced by shortening the exchange duration, in particular for effects on ettringite. This study carried out experiments with different exchange durations and IPA removal techniques to address research gaps in the literature. For 1-mm cubes of cement paste with IPA diffusion coefficient of 1 × 10{sup −11} m{sup 2}/s, the compared exchange durations are 5 min, 15 min (value from the literature), 40 min (when the mixture at the sample center achieves 95% of the drop in surface tension from water to IPA), 80 min (when the IPA/water mixture at the sample center reaches an azeotrope), 5 h (when over 99% IPA is replaced at the sample center), and 24 h (prolonged exchange). After IPA exchange, samples were either directly dried at 40 °C with flushing N{sub 2} or washed by diethyl ether prior to N{sub 2} drying. Even though the exchange duration of 40 and 80 min, in theory, can reduce the damage from capillary pressure, the nitrogen adsorption results do not show any advantage in preventing microstructural alteration. The 5-h exchange provided results similar to the 24-h exchange, but the latter induced slightly more serious chemical effects resulting from the longer contact of IPA with hydration products. In addition, the compared IPA removal techniques do not show significant differences. Therefore, this study suggests using small samples (~1 mm) for microstructural studies following IPA exchange for a period corresponding to the time when 99% of the water (mole fraction) at the sample center is replaced.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sulfate performance of blended cements (limestone and illite calcined clay) exposed to aggressive environment after casting

This paper evaluates how early aggressive exposure affects the sulfate resistance of blended cements containing limestone filler and/or calcined clay. Mortar and cement paste specimens were elaborated with different combinations of limestone filler and two different illitic calcined clays and exposed to a sodium sulfate solution shortly after casting. Assessment of sulfate resistance was based on expansion, mass variation, and compressive strength. Microscale evolution and distribution were examined by mercury intrusion porosimetry, X-ray diffraction, and scanning electron microscopy with energy-dispersive spectrometry measurements. Results prove superior sulfate resistance of compositions with high calcined clay content over limestone filler addition. Furthermore, the results reported suggest that the pozzolanic reaction progresses enough to reduce the sulfate ingress even at early exposure conditions. Therefore, calcined clay replacement can still provide effective pore refinement to limit sulfate penetration, increase strength, and reduce available CH to limit expansive phase formation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

An insight on the effect of sodium and silicon on microstructure and crystallography of high alumina cements

In the present study the influence of minor elements (Na{sub 2}O and SiO{sub 2}) on the mineralogy, chemistry and microstructure of High Alumina Cements (HACs) has been investigated. HACs have several advantages respected to Ordinary Portland Cement (OPC) but the shortage of Al-rich raw materials represents a limiting factor: re-use of Al-rich waste as raw material represents a solution but it will add minor elements to the raw meal that could change HACs properties. For the first time, four commercial HACs, doped with sodium and silicon, and one synthetic HAC, only highly doped in sodium, were studied through a multidisciplinary approach by combining conventional and unconventional analytical techniques. Results highlighted that (i) sodium and silicon were mainly incorporated in a sodium-rich phase (Na-phase, NCA{sub 2}, Na{sub 1.9}CaAl{sub 3.9}Si{sub 0.1}O{sub 8}), (ii) no minor phases such as gehlenite and/or mayenite occurred, and (iii) CA (CaAl{sub 2}O{sub 4}) and CA{sub 2} (CaAl{sub 4}O{sub 7}) revealed a limited ionic substitution.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanochemical formation of highly stable amorphous calcium carbonate in calcium silicates: Potential long-term storage of CO 2 in cement

Here, we have investigated mechanochemical reactions with the calcium silicate wollastonite to probe potential mechanisms of sequestration and long-term storage of CO 2 as mineral carbonates in cement pastes. Wollastonite, CaSiO 3 , was milled under ambient and 13 C enriched CO 2 atmospheres. Milling induced a structure change from monoclinic wollastonite-2M to triclinic-1T, consistent with high pressure treatment. The results from solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy shows this process forms an extraordinarily stable amorphous calcium carbonate (ACC) phase that remains despite a high temperature dehydration treatment (130 °C) and persists in the same form after 3 yrs. of storage at ambient conditions. Thermogravimetric analysis (TGA) of these samples indicates that ACC is produced at the similar solid concentrations in both CO 2 -enriched and ambient atmospheres. The observation of meta-stable ACC due to wollastonite carbonation may play an important role in further exploration and optimization of mineral carbonation reactions for CO 2 capturing cement formulations.

13C solid-state NMR↗
DOE OSTI2023

Prediction and demonstration of periodic tensile cracking in rate-dependent porous cement

Periodic dilation bands are shown to occur when cylinder-shaped saturated cement specimens are subjected to rapid decompression, with the spacing between the bands scaling as a power law of the decompression time. This behavior is predicted by theory, which is specified to this scenario based on prior work that was more general and applied to compaction. Specifically, the formation of the bands is shown to coincide with periodicity that naturally arises in the effective stress when the material follows a Terzaghi-type consolidation law, although in reverse for dilation and with material deformation described by a rate-dependent viscoplastic law. When strain rate is proportional to effective stress to a power that is greater than one, periodic regions of tensile effective stress arise through the poromechanical fluid-solid coupling. The theoretically-predicted exponent of the resulting power-law relationship between dilation band spacing and unloading time successfully brackets the experimental results, for which it is observed that the exponent is slightly stronger than a square-root relationship (0.28 to 0.67) at testing temperatures of 20 °C and 90 °C. Further, these results demonstrate that rapid-depressurization leads to periodic fracturing that could, on the one hand, be detrimental to the isolation provided by cement used to seal wellbores in the petroleum industry. On the other hand, the dilation bands could also be favorable to production if generated in low-permeability reservoir rocks such as shales that are targeted for petroleum production or granites that are targeted for geothermal energy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Large Cemented Gibbsite Agglomerates in Alkaline Nuclear Waste at the Hanford Site and the Impacts to Remediation

Recent work with the remediation of legacy alkaline nuclear waste has focused on nanometer and micrometer particle sizes, emphasizing how these small particles can impact efforts to treat the waste. Building upon this work, we present here findings that show very large particles (several centimeters in size) also exist in these waste which likewise play an important role in the remediation process. While large cemented gibbsite nodules have been periodically reported in acid soils in the literature, this study found similar large gibbsite agglomerates (7 cm in diameter) in alkaline nuclear waste, the first time that such large agglomerates have been identified in an alkaline environment. The morphology of the gibbsite in the agglomerates that were grown over more than 40 years of storage in the waste tank were similar to the much smaller agglomerates that have been reported in previous shorter term studies. Fluid dynamics calculations indicate that these cemented particles would be difficult to mobilize with standard jet slurry technologies, which is consistent with their residence in the waste heel after jet sluicing of the tank.

agglomerates, alkaline nuclear waste↗
DOE OSTI2025

In-situ neutron radiography of pore-water movement in portland cement mortar under subzero temperature exposure: Insights from D 2 O-H 2 O systems

Neutron radiography was employed in this study to monitor real-time pore water movement in portland cement mortar exposed to subzero temperatures, providing novel insights into freeze-thaw (F-T) damage mechanisms. Deuterated water (D 2 O) was used to hydrate the cement in the mortar specimens, and the pore structure was saturated with water (H 2 O), allowing for a contrast that enabled detailed tracking of water movement predominantly in the pore structure. Furthermore, the mortar sample was placed on a chiller plate set to subzero temperatures, thereby providing a one-dimensional temperature gradient vertically in the sample. Neutron radiography revealed that unfrozen water migrated upward as the freezing front advanced, which can create hydraulic pressure within the mortar microstructure and may contribute to the initiation and propagation of microcracks during F-T cycles. Additional characterization of the concrete made with D 2 O showed a marked contrast to the samples made with H 2 O, including delayed hydration, diminished compressive strength, and greater porosity. Therefore, while mortar made with D 2 O allowed for greater neutron contrast to the pores filled with H 2 O, further study is required to produce mortars with similar properties to those made with H 2 O. In addition, further refinement is needed to the radiography experiment to allow for greater control of temperatures and potential quantification of the water concentration.

Air-void system↗
DOE OSTI2017

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

The metallic binder phase dictates the toughening behavior of WC-Co cemented carbides (hardmetals), even though it occupies a relative small fraction of the composite. Studies on deformation and phase transformation of the binder constituent are scarce. Grinding represents a key manufacturing step in machining of hardmetal tools, and is well-recognized to induce surface integrity alterations. In this work, metallurgical alterations of the binder phase in ground WC-Co cemented carbides have been assessed by a combination of electron back scattered diffraction and transmission electron microscopy techniques. The Co-base binder experiences a martensitic phase transformation from fcc to hcp crystal structure, predominantly in the first 5 μm below the surface. The hcp fraction decreases gradually along a depth of 10 μm. Surface Co displays severe plastic deformation under the highest strain, resulting in formation of nanocrystalline grains in the first micrometer below the surface. Microstructural refinement within the binder phase is observed even at greater depth. Stacking faults were detected in most of the refined grains. The metallurgical alterations of the binder phase modify the local stress distribution during grinding, which affects the discerned subsurface microcracking. The resulting residual stress profile is the sum of multiple subsurface changes, such as phase transformation, severe plastic deformation and grain refinement, where it is discerned that the depth profile of the transformed hcp-Co fraction coincides with the grinding-induced residual stress profile.

36 MATERIALS SCIENCE↗