A Study on the Minimum Paste Volume in the Design of Concrete Mixture

Fowler, David W.,Hahn, Michael De Moya,Rached, Marc,Choi, Doo-Sun,Choi, Jae-Jin Korea Concrete Institute 2008 International Journal of Concrete Structures and M Vol.2 No.2

Optimization of concrete mixing system is very important for the production of quality mixture of concrete and requires very complicated, specialized knowledge as there are a variety of variables that influence the result. One of the methods of optimizing the concrete mixing system is to minimize the volume of cement paste which, in turn, means maximizing the volume of aggregate. The purpose of this study is to determine the minimum volume of cement paste used in the design of concrete mixture and to design the optimum concrete mixing system based on the fluidity of mortar and concrete. In determining the minimum volume of cement paste, experiments of mortar and concrete were performed based on their workability, material segregation and bleeding. Type of aggregate, granularity distribution and sand percentage were used as test parameters and measurements were taken of the distribution of granularity, usage of HRWRA, minimum volume of paste and drying shrinkage and compressive strength of concrete.

A Study on the Minimum Paste Volume in the Design of Concrete Mixture

David W. Fowler,Michael De Moya Hahn,Marc Rached,Doo-Sun Choi,Jae-Jin Choi 한국콘크리트학회 2008 International Journal of Concrete Structures and M Vol.2 No.2

2SK-8 Role of Conductive Fillers on Properties of Polypropylene Composites for PEMFC Bipolar plates

( Rungsima Yeetsorn ),( Michael W. Fowler ),( Costas Tzoganakis ),( Chaiwat Prapainainar ),( Walaiporn Prissanaroon Ouajai ) 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.1

Due to increasing environmental concerns and escalating oil prices, increasing attention is being paid to fuel cell technologies. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically bipolar plates. Conductive thermoplastic composites are thought to be one of the most promising candidate materials to substitute for metallic and graphite materials in bipolar plates for low temperature fuel cells, such as Proton Exchange Membrane Fuel Cell (PEMFC) or Direct Methanol Fuel Cell (DMFC). Bipolar plates made from thermoplastic carbon composites are light in weight and can be shaped in mold. Research work on bipolar plate materials will bring about the next significant improvement in fuel cell performance by lowering the size, weight and cost of stacks. Our research group focuses on using polypropylene/conductive filler composites with low filler loading as materials for bipolar plate production. The selected conductive fillers used in our work are graphite, carbon fiber, carbon black, and graphene. These composites have a major advantage in that they can be produced by a conventional low-cost injection or compression molding techniques. However, it is difficult to meet desirable conductivity when using the composite plates while maintaining processability. Surface, contact, and volume resistance occurring in fuel cells causes low efficiency fuel cells containing the composite bipolar plates compared to fuel cells containing metallic or graphite bipolar plates. In this regard, several approaches, such as introducing small amounts of polypyrrole to the composites, coating polypyrrole via chemical polymerization or coating copper via electroless deposition on a bipolar plate surface, and inserting metal sheet into the composite plates, were created for reducing the resistance.

The Physical Properties of Granite Microfines and the Workability of Mortar with Granite Microfines

Koehler, Eric,Hahn, Michael De Moya,Trachet, Alison,Rached, Marc,Choi, Jae Jin,Fowler, David Korean Recycled Construction Resources Institute 2009 한국건설순환자원학회지 Vol.4 No.3

This paper summarizes the analysis of granite microfines from California for use in portland cement concrete. For reference, the granite microfines were compared to microfines used in previous International Center for Aggregates Research(ICAR) projects. The particle shape characteristics, based on the packing density results, were assessed and apparent clay content, based on the methylene blue value test, was evaluated. Also, the physical properties of the microfines were confirmed in self-consolidating mortar mixtures.

Development of integrated waste management options for irradiated graphite

Alan Wareing,Liam Abrahamsen-Mills,Linda Fowler,Michael Grave,Richard Jarvis,Martin Metcalfe,Simon Norris,Anthony William Banford 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.5

The European Treatment and Disposal of Irradiated Graphite and other Carbonaceous Waste projectsought to develop best practices in the retrieval, treatment, and disposal of irradiated graphite includingother irradiated carbonaceous waste such as structural material made of graphite, nongraphitized carbonbricks, and fuel coatings. Emphasis was given on legacy irradiated graphite, as this represents a significantinventory in respective national waste management programs. This paper provides an overview ofthe characteristics of graphite irradiated during its use, primarily as a moderator material, within nuclearreactors. It describes the potential techniques applicable to the retrieval, treatment, recycling/reuse, anddisposal of these graphite wastes. Considering the lifecycle of nuclear graphite, from manufacture to finaldisposal, a number of waste management options have been developed. These options consider thetechniques and technologies required to address each stage of the lifecycle, such as segregation, treatment,recycle, and ultimate disposal in a radioactive waste repository, providing a toolbox to aid operatorsand regulators to determine the most appropriate management strategy. It is noted that nationalwaste management programs currently have, or are in the process of developing, respective approachesto irradiated graphite management. The output of the Treatment and Disposal of Irradiated Graphite andother Carbonaceous Waste project is intended to aid these considerations, rather than dictate them.

Searching for Transit Timing Variations and Fitting a New Ephemeris to Transits of TrES-1 b

Paige Yeung,Quinn Perian,Peyton Robertson,Michael Fitzgerald,Martin Fowler,Frank Sienkiewicz,Kalee Tock 한국천문학회 2022 Journal of The Korean Astronomical Society Vol.55 No.4

Based on the light an exoplanet blocks from its host star as it passes in front of it during a transit, the mid-transit time can be determined. Periodic variations in mid-transit times can indicate another planet's gravitational influence. We investigate 83 transits of TrES-1 b as observed from 6-inch telescopes in the MicroObservatory robotic telescope network. The EXOTIC data reduction pipeline is used to process these transits, fit transit models to light curves, and calculate transit midpoints. This paper details the methodology for analyzing transit timing variations (TTVs) and using transit measurements to maintain ephemerides. The application of Lomb-Scargle period analysis for studying the plausibility of TTVs is explained. The analysis of the resultant TTVs from 46 transits from MicroObservatory and 47 transits from archival data in the Exoplanet Transit Database indicated the possible existence of other planets affecting the orbit of TrES-1 and improved the precision of the ephemeris by one order of magnitude. We now estimate the ephemeris to be 2455489.66026 BJD_{TDB} ± 0.00044 d + (3.0300689 ± 0.0000007) d × epoch. This analysis also demonstrates the role of small telescopes in making precise mid-transit time measurements, which can be used to help maintain ephemerides and perform TTV analysis. The maintenance of ephemerides allows for an increased ability to optimize telescope time on large ground-based telescopes and space telescope missions.

Molybdenum-Based Electrocatalysts for Direct Alcohol Fuel Cells: A Critical Review

Gaurav Kumar Yogesh,Rungsima Yeetsorn,Waritnan Wanchan,Michael Fowler,Kamlesh Yadav,Pankaj Koinkar The Korean Electrochemical Society 2024 Journal of electrochemical science and technology Vol.15 No.1

Direct alcohol fuel cells (DAFCs) have gained much attention as promising energy conversion devices due to their ability to utilize alcohol as a fuel source. In this regard, Molybdenum-based electrocatalysts (Mo-ECs) have emerged as a substitution for expensive Pt and Ru-based co-catalyst electrode materials in DAFCs, owing to their unique electrochemical properties useful for alcohol oxidation. The catalytic activity of Mo-ECs displays an increase in alcohol oxidation current density by several folds to 1000-2000 mA mg_Pt^-1, compared to commercial Pt and PtRu catalysts of 10-100 mA mg_Pt^-1. In addition, the methanol oxidation peak and onset potential have been significantly reduced by 100-200 mV and 0.5-0.6 V, respectively. The performance of Mo-ECs in both acidic and alkaline media has shown the potential to significantly reduce the Pt loading. This review aims to provide a comprehensive overview of the bifunctional mechanism involved in the oxidation of alcohols and factors affecting the electrocatalytic oxidation of alcohol, such as synthesis method, structural properties, and catalytic support materials. Furthermore, the challenges and prospects of Mo-ECs for DAFCs anode materials are discussed. This in-depth review serves as valuable insight toward enhancing the performance and efficiency of DAFC by employing Mo-ECs.