• Journal of Electrochemical Science and Technology
• /
• v.12 no.4
• /
• pp.440-452
• /
• 2021

Enhancement of durability and reduction of maintenance cost of concrete, with the implementation of various approaches, has always been a matter of concern to researchers. The integration of pozzolans as a substitute for cement into the concrete is one of the most desirable technique. Silica fume (SF) and colloidal nanosilica (CS) have received a great deal of interest from researchers with their significant performance in improving the durability of concrete. The synergistic role of the micro and nano-silica particles in improving the main characteristics of cemented materials needs to be investigated. This work aims to examine the utility of partial substitution of cement by SF and CS in binary and ternary blends in the improvement of the durability characteristics linked to resistance for electrochemical corrosion using electrical resistivity and half-cell potential analysis and chloride penetration trough rapid chloride penetration test. Furthermore, the effects of this silica mixture on the compressive strength of concrete under normal and aggressive environment have also been investigated. Based on the maximum compression strength of the concrete, the optimal cement substituent ratios have been obtained as 12% SF and 1.5% CS for binary blends. The optimal CS and SF combination mixing ratios has been obtained as 1.0% and 12% respectively for ternary blends. The ternary blends with substitution of cement by optimal percentage of CS and SF exhibited decreased rate for electrochemical corrosion. The strength and durability studies were found in consistence with the microstructural analysis signifying the beneficiary role of CS and SF in upgrading the performance of concrete.

• Journal of the Korean Geotechnical Society
• /
• v.39 no.7
• /
• pp.49-56
• /
• 2023

Gravel is commonly employed to enhance the bearing capacity of foundations and provide stable support for structures. However, effectively assessing the ground characteristics in the presence of gravel poses significant challenges. This study aims to compare the resolution of ground containing gravel using electrical resistivity, elastic wave surveys, and ground penetration radar (GPR). Nondestructive methods are applied at construction sites where soil improvement is carried out using gravel. The experiments focus on shallow depths, and the obtained results cover depths up to 2 m. Both the electrical resistivity and elastic wave techniques exhibit similar behavior in their findings, indicating comparable outcomes. However, GPR has limitations in observing the characteristics of ground with gravel. Dynamic cone-penetration tests were conducted to validate these findings. The electrical resistivity and elastic wave profiles exhibited similar behaviors in localized areas, further supporting their compatibility and reliability.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.3
• /
• pp.80-87
• /
• 2010

The purpose of this paper is to analyze the effects of ethanol blending ratio and fuel temperature in diesel-ethanol blended fuel on the spray-atomization characteristics in a high pressure common-rail injection system. In this work, a diesel fuel and three blended fuels were used as test fuels. Blended fuels were made by blending ethanol with a purity 99.9% to diesel fuel, from 0% to 30%. In order to keep diesel-ethanol blending stability, 5% of biodiesel fuel as volumetric ratio was added into test fuels. The fuel temperature was controled in steps with 40K, from 290K to 370K. Macroscopic spray characteristics were investigated by analyzing the spray tip penetration and spray cone angle through spray images obtained from visualization system. In addition, in order to study microscopic spray characteristics of ethanol blended fuels, the droplet diameter, was analyzed using the droplet measuring system. It is revealed that the spray tip penetration is similar regardless of ethanol blending ratio. As ethanol blending ratio is increased, the spray cone angle becomes wider. It is shown that the spray cone angle is affected by low viscosity and density of ethanol. As the fuel temperature increases, the spray tip penetration and spray cone angle become shorter and narrower respectively. The SMD of ethanol blending fuels is smaller than that of diesel fuel because of low viscosity and surface tension of ethanol.

• Tribology and Lubricants
• /
• v.37 no.5
• /
• pp.189-194
• /
• 2021

A straightforward, yet effective surface modification method of stainless steel mesh and its interesting anti-wetting characteristics are reported in this study. The stainless steel mesh is electrochemically etched, and the specimen has both micro and nano-scale structures on its surface. This process transforms the two types of mesh specimens known as the regular and dense specimens into hydrophobic specimens without applying any hydrophobic chemical coating process. The fundamental wettability of the modified mesh is analyzed through a dedicatedly designed experiment to investigate the waterproof characteristics, for instance, the penetration threshold. The waterproof characteristics are evaluated in a manner that the modified mesh resists as high as approximately 2.7 times the pressure compared with the bare mesh, i.e., the non-modified mesh. The results show that the penetration threshold depends primarily on the advancing contact angles, and the penetration stop behaviors are affected by the contact angle hysteresis on the surfaces. The findings further confirm that the inexpensive waterproof meshes created using the proposed straightforward electrochemical etching process are effective and can be adapted along with appropriate designs for various practical applications, such as underwater devices, passive valves, and transducers. In general, , additional chemical coatings are applied using hydrophobic materials on the surfaces for the applications that require water-repelling capabilities. Although these chemical coatings can often cause aging, the process proposed in this study is not only cost-effective, but also durable implying that it does not lose its waterproof properties over time.

• Journal of electromagnetic engineering and science
• /
• v.6 no.2
• /
• pp.123-129
• /
• 2006

This paper presents a method of reducing penetration of penetrated electromagnetic fields through a narrow slot with parallel wire arrays in a planar conducting screen of infinite extent. An integral equation for the aperture electric field on the narrow slot is derived and solved by applying Galerkin's method of moments. When a plane wave is excited to the narrow slot, the aperture electric field is easily controlled by the parallel wire arrays connected on the slot and therefore the magnitude of the penetrated electric field is effectively reduced by loading the parallel wire arrays. The numerical results show that the magnitude of the penetrated electromagnetic field can be effectively reduced by installing the parallel wire arrays on the slot. The results of the calculated penetration electric fields are in good agreement with that of the measured results.

• Structural Engineering and Mechanics
• /
• v.55 no.3
• /
• pp.583-603
• /
• 2015

There are so many applications of perforated pates with various penetration patterns. If they are penetrated regularly, it can be represented by solid plate with equivalent material properties, which has a benefit of finite element modelling and reducing computation time for the analysis. Because the equivalent material properties suggested already are not proper to be applicable for the dynamic analysis, it is necessary to extract the equivalent material properties for the dynamic analysis. Therefore, in this study, the equivalent modulus of elasticity are obtained for the perforated plate with a triangular penetration pattern by comparing the natural frequencies of the perforated plate with those of solid plate, which are represented with respect to the ligament efficacy. Using the equivalent material properties suggested, the modal analyses of the partially perforated rectangular plate with a triangular penetration pattern are performed and its applicability is shown by comparing natural frequencies of perforated and homogeneous solid plates from finite element method and analytical method.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.573-583
• /
• 1994

In this study, the shock characteristics for high velocity impact phenomena during the initial shock state by the long rod penetrator are calculated. From these results we re-analyze the one-dimensional hydrodynamic penetration theory by introducing the effective area ratio calculated from the mushroomed strain which is dependent on impact velocity. Calculated penetration depth and mushroomed strain show good agreement with high velocity impact experimental data. In addition we visualize the shock wave propagation in a transparent acryle block.

• Journal of Ocean Engineering and Technology
• /
• v.8 no.1
• /
• pp.41-49
• /
• 1994

The leak-before-break(LBB) design on the large structures such as ship's hull, tank structure, pressure vessels etc. is one of the most inportant subjects for the evaluation and the assurance of safety. In these structures, various loads are acting. In some structural members, therefore, out-of-plane stress due to bending often may become with in-plane stress due to stretching. In the present report, the characteristics of fatigue life and peneration behaviour from a surface cracked plate under combined tension and bending have been studied experimentally and analytically by using eccentricity. Estimation of fatigue crack growth was done with the Newman-Raju formula before penetration, and with the stress intensity factor after penetration proposed by the author. Calculated aspect ratio showed the good agreement with the experimental result. It was also found that particular crack growth behaviour and crack shape after penetration can be satisfactorily evaluated using the K solution proposed.

• Computers and Concrete
• /
• v.6 no.5
• /
• pp.421-435
• /
• 2009

Chloride induced corrosion is a concern that governs the durability of concrete structures in marine environments, especially in tidal environments. During the service lives of concrete structures, internal cracks in the concrete cover may appear due to imposed loads, accelerating chloride penetration because of the simultaneous action of environmental and service structural loads. This paper investigated the effects of cyclic flexural loads on chloride diffusion characteristics of plain concretes, and proposed a model to predict the chloride penetration into plain concretes subjected to both tidal environments and different cyclic flexural load levels. Further, a new experiment was performed to verify the model. Results of the model using Finite Difference Method (FDM) showed that the durability of concretes in tidal environments was reduced as cyclic flexural load levels, SR, increased, and the modeling results fitted well with the experimental results.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.946-951
• /
• 2001

This experimental study is to investigate the intermittent spray characteristics of a pintle nozzle. High speed camera used in this expreiment with 9000fps. The factor, which controls the diesel spray, is the Injection pressure, ambient pressure and ambient temperature. In this paper, experiments were conducted free spray for the ambient pressure(3, 4, 5Mpa), nozzle Injection pressure(10, 14, 18MPa) and ambient temperature(293, 473K). With the higher opening pressure, the spray tip velocity and spray penetration increases while the spray angle decreases, On the other hand, With the higher ambient pressure, the spray angle increase while the spray tip penetration and spray tip velocity decrease. also, With the higher ambient temperature, the spray penetration decrease while the spray angle decrease.