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Huang C.-H.,Dahan Institute of Technology | Lin S.-K.,National Chung Hsing University | Chang C.-S.,Sudan University of Science and Technology | Chen H.-J.,National Chung Hsing University
Construction and Building Materials | Year: 2013

Two types of Class F fly ash with 4.6% and 7.8% loss on ignition were used for an experimental investigation dealing with concrete incorporating very high volumes of Class F fly ash (HVFA). A rational mix design method was developed for concrete with 20-80% fly ash replacement for cement. Tests were performed for fresh and hardened concrete properties. Test results indicated that the setting times and the air content of fly-ash concrete increased as the fly ash replacement level increased. The compressive and flexural strength of the HVFA concrete mixtures demonstrated continuous and significant improvement at late ages of 91 and 365 days. Relation was formulated for flexural and compressive strength for all grades of HVFA concrete. The concrete mixture containing low-LOI fly ash exhibited superior mechanical properties than those of the corresponding mixture containing high-LOI fly ash. These results confirm the feasibility that up to 80% of Class F fly ash can be suitably used as cement replacement in concrete by using a rational mixture proportions. © 2013 Elsevier B.V. All rights reserved. Source


Huang C.-H.,Dahan Institute of Technology | Wang S.-Y.,National Chung Hsing University
Construction and Building Materials | Year: 2013

This study assesses the possible use of water treatment sludge for the production of lightweight aggregate (LWA), and focuses on the engineering properties of concrete made from this LWA. The experiments in this study involve 10 sludges from ten water treatment plants in Taiwan. All sludges can be used to manufacture LWAs in the laboratory, and exhibit a particle density (ρa) of 0.65-2.05 g/cm3 and water absorption of 0.5-15%. Five sludges are suitable for manufacturing both structural LWA (ρa = 1.2-1.8 g/cm3) and non-structural LWA (ρa < 1.0 g/cm3), and the other five sludges are only suitable for manufacturing structural LWA. The sludge collected from the Hsing-Zu plant was successfully used to produce both structural and non-structural LWA on a large scale using a commercial rotary kiln. The resulting aggregates possessed a particle density of 1.35 g/cm3 or 0.98 g/cm3 and a bulk density of 726 kg/m3 or 518 kg/m3 for the structural LWA and non-structural LWA, respectively. The structural LWA meets the ASTM C330 requirements, with a bulk density less than 880 kg/m3 for light coarse aggregate, and is a suitable LWA for structural concrete. The engineering properties of the concrete made from the structural LWA comply with the requirements of structural lightweight concrete. © 2013 Elsevier Ltd. All rights reserved. Source


Fu Y.-P.,National Dong Hwa University | Li C.-H.,National Dong Hwa University | Hu S.-H.,Dahan Institute of Technology
Journal of the Electrochemical Society | Year: 2012

This study investigates the electrochemical properties of three different configurations of Sm 0.5Sr 0.5CoO 3-δ (SSC)-based cathodes and attempts to discover a potential approach applicable to solid oxide fuel cells (SOFCs). The functionally gradient SSC cathode and Ce 0.8Sm 0.2O 1.9 (SDC)-infiltrated SSC cathode both reveal the better electrochemical properties compared to that of the 70 SSC- 30 SDC composite cathode. The functionally gradient Sm 0.5Sr 0.5CoO 3-δ cathode with better interface of SSCSDC may be achieved by the gradual change in composition from electrolyte to cathode, resulting in the decline in charge transfer resistance and gas phase diffusion resistance. Whereas, the dramatic decrease in cathode polarization resistance for SDC-infiltrated SSC cathode is mainly attributed to the creation of SDCSSC phase boundaries. The newly formed SDC on the SSC surface with highly porous would allow gas-phase molecules to easily diffuse to the SDCSSC boundaries, which considerably increase the electrochemical sites for oxygen reduction reaction (ORR). The SDC-infiltrated SSC cathode reveals the lowest cathode polarization resistance (R P), the lowest activation energies of cathode polarization resistance and the lowest over activation energy for the ORR among all cathode configurations. Noticeably, the cathode performance in SOFCs can be significantly improved by infiltrating nanoparticles of SDC into an SSC porous backbone. © 2012 The Electrochemical Society. Source


Liu H.-Y.,Dahan Institute of Technology | Yen R.Y.,Tamkang University
IEEE Transactions on Vehicular Technology | Year: 2010

For joint maximum-likelihood (ML) frequency tracking and channel estimation using orthogonal frequency-division multiplexing (OFDM) training blocks in OFDM communications over mobile wireless channels, a major difficulty is the local extrema or multiple-solution complication arising from the multidimensional log-likelihood function. To overcome this, we first obtain crude ML frequency-offset estimators using single-time-slot samples from the received time-domain OFDM block. These crude frequency estimators are shown to have unique closed-form solutions. We then optimally combine these crude frequency estimators in the linear-minimum-mean-square-error (LMMSE) sense for a more accurate solution. Finally, by alternatively updating the LMMSE frequency estimator and the ML channel estimator through adaptive iterations, we successfully avoid the use of a multidimensional log-likelihood function, hence obviating the complex task of global solution search and, meanwhile, achieve good estimation performance. Our estimators have mean square errors (MSEs) tightly close to Cramer-Rao bounds (CRBs) with a wide tracking range. © 2006 IEEE. Source


Li C.-H.,National Dong Hwa University | Hu S.-H.,Dahan Institute of Technology | Tay K.-W.,Wufeng University | Fu Y.-P.,National Dong Hwa University
Ceramics International | Year: 2012

This study investigates Sm 0.5Sr 0.5CoO 3-δ (SSC)-Ce 0.8Sm 0.2O 1.9 (SDC) composite cathodes with a gradual change in composition from electrolyte to the cathode in an attempt to discover a potential approach applicable to solid oxide fuel cells (SOFCs). The gradual change in composition from electrolyte to cathode shows the decline in charge transfer resistance (R 2) and gas phase diffusion resistance (R 3). Because the value of R 3 is always larger than R 2 and R 3 significantly dominates the total cathode polarization resistance (R P) at temperatures within the range of 750-850 °C, i.e., in this temperature range, the rate-determining step is dominated by the diffusion or dissociative adsorption of oxygen. The functionally gradient cathode with a graded interface between cathode and electrolyte reveals both a higher exchange current density (i 0) and a lower activation energy for oxygen reduction reaction (ORR), which suggests that the ORR kinetics can be improved by using the configuration of a functionally gradient cathode. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Source

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