• Tunnel and Underground Space
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• v.14 no.1
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• pp.1-15
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• 2004

The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

• Journal of Korean Society of Steel Construction
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• v.23 no.6
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• pp.737-745
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• 2011

A concrete-filled tube is a concrete-filled steel tube structure. The steel tube confines the concrete to increase the compressive strength, and the concrete contains the buckling of the tube. CFT structures require a diaphragm to prevent buckling of steel at connections. An outer diaphragm has better concrete filling than a through diaphragm due to a large bore, but being larger than the through diagram, it has poorer constructability and cooperation with building equipment. In this study, a CFT structure that uses different types of diaphragms in its upper and lower connections to improve the concrete filling was tested and analyzed via the FEM program. The building structure had a floor slab that was unified with the upper diaphragm, so the outer diaphragm was placed at the upper bound. Moreover, the through diaphragm was placed at the lower connection to avoid obstruction from building equipment. The CFT structure with the improved concrete filling showed the same structural behavior as the CFT structure with the use of the same type of diaphragms at the upper and lower connections.

• Tribology and Lubricants
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• v.33 no.1
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• pp.15-22
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• 2017

Because the running speed of vehicles is increasing and a shorter braking distance is required, high heat-resistant brake pads are needed to satisfy the requirements of customers and car makers. In the near future, hazardous materials such as Cu, Cr, Zn, and Sb will be restricted from use in friction materials. Ceramic composites reinforced by carbon fibers are good candidates for eco-friendly friction materials. In this study, we develop ceramic composite friction materials. The friction materials are composed of carbon fibers, Si, SiC, graphite, and phenol resin and are prepared by hot forming and heat treatment at high temperatures. The density, void ratio, and compressive strength are $1.59-1.66g/cm^3$, 16.6-20, and 70-90 MPa, respectively. Friction and wear tests are performed using a pin-on-plate-type reciprocating friction tester at 25, 100, and $200^{\circ}C$. The counterpart material is a CrMoV steel extracted from a KTX brake disc. Friction coefficient, wear amount, and wear mechanism are measured and examined. We determine that the friction coefficients depend on the temperature and the fluctuation of the friction coefficients is larger at higher temperatures. The amount of wear increases with the surface temperatures of the specimens. The tribological properties of the developed composites are similar to those of a Cu-based sintered friction material. Through this study, it is confirmed that ceramic composite materials can be used as friction materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.443-449
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• 2012

Nanoskins were fabricated on a Ti-6Al-4V material by carrying out various surface treatments, i.e., deep rolling, laser shot peening, and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular for industrial applications. Fatigue tests were carried out using material test system (MTS); these tests included the axial loading tension-compression fatigue test (R = -1, RT, 5 Hz, sinusoidal wave) and rotating bending fatigue test (R = -1, RT, 3200 rpm). The analysis of the crack initiation pattern in the UNSM-treated material indicated that the crack was interior originating in the axial loading tension-compression cycle, and was surface originating in the bending fatigue test. UNSM treatment significantly improved the fatigue strength for the regime of above $10^6$ cycles that S-N curve of rotating bending stress clearly show the performance of a 5 mm titanium specimen after UNSM treatment is similar to that of an untreated 6 mm titanium specimen.

• Applied Chemistry for Engineering
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• v.20 no.5
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• pp.505-510
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• 2009

It is well known that the properties of concrete such as the compressive strength, water permeability, water tightness and durability are affected by micro-structure in hardened cement paste. Especially, for durability of concrete, watertightness of cementitious materials is the most critical property among various properties. Recently, many types of material such as organic and/or inorganic materials are used for watertightness of concrete. In this study, we examined the effect of fluorine-based emulsion on watertightness property. And we also discussed the change of microstructure and formation of hydrates in hardened cement paste by the addition of fluorine-based emulsion. Cement paste with fluorine-based emulsion showed improvement of watertightness by the surface activation of cement paste and by formation of $CaF_2$ fine crystals in cement pore structure.

• Analytical Science and Technology
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• v.15 no.3
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• pp.256-262
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• 2002

After porous filters were manufactured using cordierite powder whose mean paricle size was 200${\mu}m$, they were loaded with catalysts such as $V_2O_5$, CuO and $LaCoO_3$ by vacuum impregnation method. And the NOx/SOx simultaneous removal efficiency was measured by passing NO and $SO_2$ through catalyst-loaded ceramic filters. The cordierite porous filters had the apparent porosity of 61.6%, the compressive strength of 12.3 MPa and the pressure drop of 147 pa at the face velocity of 5 cm/sec. According to the analysis of NO/$SO_2$ simultaneous removal efficiency, perovskite $LaCoO_3$ catalyst was the most efficient for the simultaneous NO and $SO_2$ removal. The $LaCoO_3$ catalyst-loaded filter could remove more than 90% for NO and more than 80% for $SO_2$.

• Journal of Conservation Science
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• v.36 no.5
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• pp.339-350
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• 2020

This study attempted to apply a hybrid technology that integrated mineral-based fillers and water-repellent agents to control the efflorescence that results from the use of inorganic binders, for the conservation treatment (surface finishing) of cultural heritage materials made up of stone. Herein, different types of mixing ratios of a filler (silica fume 3.4%) and a water repellent (silane-siloxane 1%) were selected for fabricating the inorganic binder, and it was determined that the ratio selected by weight is effective in controlling efflorescence substances. In addition, it was identified that the inorganic binder with the mixing ratio resulted in a higher compressive strength than the standard (20MPa), and the water permeability resistance was high with low water absorption. The result of ion elution from the bilder showed that a smaller number of ions was observed to affect the efflorescence (directly and indirectly) as compared to that of the control group, which was considered to be relatively stable.

• The Journal of Engineering Geology
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• v.21 no.4
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• pp.295-304
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• 2011

The first step in improving our understanding of uncertainties suclt as rock mass strength parameters and deformation modulus in rock masses around high-level radioactive waste disposal repositories, for improved safety, is to study the process of crack development in intact rock. Therefore, in this study, the fracture process and crack development were examined in samples of KURT granite taken from the KAERI Underground Research Tunnel (KURT), based on acoustic emission (AE) and moment tensor analysis. The results show that crack initiation, coalescence, and unstable crack occurred at rock uniaxial compressive strengths of 0.45, 0.73, and 0.84, respectively. In addition, moment tensor analysis indicated that during the early stage of loading, tensile cracks were predominant. With increasing applied stress, the number of shear cracks gradually increased. When the applied stress exceeded the stress level required for crack damage, unstable shear cracks which directly result in failure of the rock were generated along the failure plane.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.577-582
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• 2016

In this study, we compared and analyzed the flame retardancy and mechanical properties of three different rigid polyurethane foams (RPUF) containing noble non-halogen phosphorus flame retardant (BHP-RPUF) or halogen-phosphorus flame retardant (TCPP-RPUF) or no flame retardant material (Pure-RPUF). The noble phosphorus-based flame retardant, bis(3-(3-hydroxypropoxy)propyl) phenyl phosphate (BHP), was synthesized by the reaction between disodium phenyl phosphate and 3-chloro-1-propanol. Through universal testing machine (UTM) experiments, the compressive strength of BHP-RPUF was similar to that of TCPP-RPUF. From the result of foam morphology analysis, it was confirmed that BHP-RPUF has the lowest thermal conductivity of $0.023W/m{\cdot}K$. We also measured the size of air bubbles using reaction velocity and SEM, and analyzed how they affect the thermal conductivity. In addition, the heat-resisting property was investigated through TGA analysis. The limited oxygen index (LOI) test confirmed that BHP had the ability to increase the flame retardancy of RPUF.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.178-185
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• 2011

Recently depletion of natural resources makes a deficiency of sand aggregation in the concrete works. In this study, the quality characteristics of concrete and aggregate according to blending fine aggregate in the river sand and the crash sand was analyzed by Normal method and Driscoll method which has used mixing of fine aggregate for asphalt mostly. Application of Discoll method to blend fine aggregate for concrete was studied in the first step to blend fine aggregates concrete. The fineness modulus, grading, slump, air content and compressive strength were tested by the two method, the results of Driscoll method was very similar to degree of err limits in comparison with those of Normal method in the same condition. As a result, Driscoll method is reasonable to use the fine aggregates mixture for concrete in river sand and crash sand.