• Advances in concrete construction
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• 제15권6호
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• pp.431-444
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• 2023

This study investigated the use of latex-modified sand concrete reinforced with sisal fibers (LMSC) as a repair material. Notably, no prior research has explored the application of LMSC for this purpose. This paper examines the interface bond strength and the type of failure between LMSC as a repair material and the normal concrete (NC) substrate utilising four different surfaces: without surface preparation as a reference (SR), hand hammer (HA), sandblasted (SB), and grooved (GR). The bond strength was measured by bi-surface shear, splitting tensile, and pull-off strength tests at 7, 28, and 90 days. Scanning electron microscopy analysis was also performed to study the microstructure of the interface between the normal concrete substrate and the latex-modified sand concrete reinforced with sisal fibers. The results of this study indicate that LMSC has bonding strength with NC, especially for HR and SB surfaces with high roughness. Therefore, substrate NC surface roughness is essential in increasing the bonding strength and adhesion. Eventually, The LMSC has the potential to repair and rehabilitate concrete structures.

• 한국도로학회논문집
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• 제19권6호
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• pp.129-137
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• 2017

PURPOSES : The purpose of this study is to develop bridge deck concrete materials based on ordinary Portland cement concrete, and to evaluate the applicability of the developed materials through material properties tests. METHODS : For field implementation, raw material (cement, fine aggregate, and coarse aggregate) properties, fresh concrete properties (slump and air content), strength (compressive, flexural and bond strength) gain, and durability (freeze-thaw resistance, scaling resistance, and rapid chloride penetrating resistance) performance were evaluated in the laboratory. RESULTS : For the selected binder content of $410kg/m^3$, W/B = 0.42, and S/a = 0.48, the following material performance results were obtained. Considering the capacity of the deck finisher, a minimum slump of 150 mm was required. At least 6 % of air content was obtained to resist freeze-thaw damage. In terms of strength, 51.28 MPa of compressive strength, 7.41 MPa of flexural strength, and 2.56 MPa of bond strength at 28 days after construction were obtained. A total of 94.9 % of the relative dynamic modulus of elasticity after 300 cycles of freeze-thaw resistance testing and $0.0056kg/m^2$ of weight loss in a scaling resistance test were measured. However, in a chloride ion penetration resistance test, the result of 3,356 Coulomb, which exceeds the threshold value of the standard specification (1000 Coulomb at 56 days) was observed. CONCLUSIONS : Instead of using high-performance modified bridge deck materials such as latex or silica fume, we developed an optimum mix design based on ordinary Portland cement concrete. A test construction was carried out at ramp bridge B (bridge length = 111 m) in Gim Jai City. Immediately after the concrete was poured, the curing compound was applied, and then wet mat curing was applied for 28 days. Considering the fact that cracks did not occur during the monitoring period, the applicability of the developed material is considered to be high.

• Computers and Concrete
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• 제3권1호
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• pp.17-28
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• 2006

Replacement of actual stress distribution in a reinforced concrete (RC) flexural member with a simpler geometrical shape, which maintains magnitude and location of the resultant compressive force, is an acceptable conceptual trick. This concept was originally perfected for normal strength concrete. In recent years, high strength concrete (HSC) has been introduced and widely used in modern construction. The stress block parameters require updating to account for special features of HSC in the design of flexural members. In future, more varieties of concrete may be developed and a corresponding design procedure of RC flexural members will be required. The usual practice is to conduct large number of experiments on various sizes of specimen and then evolve an empirical relation. This paper presents a numerical procedure through which the stress block parameters can be numerically derived for a given strain ratio variation. The material model for concrete is presented and computational procedure is described. This procedure is illustrated with several variations of strain ratio. The advantages of numerical procedure are that it costs less and it can be used with new material models for any new variety of concrete.

• Design & Manufacturing
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• 제2권5호
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• pp.43-47
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• 2008

Micro Electrochemical Machining(Micro ECM) has traditionally been used in highly specialized fields such as those of the aerospace and defense industries. It is now increasingly being applied in other industries where parts with difficult-to-cut material, complex geometry and tribology such as compute. hard disk drive(HDD) are required. Pulse Electrochemical Micro-machining provides an economical and effective method for machining high strength, high tension, heat-resistant materials into complex shapes such as turbine blades of titanium and aluminum alloys. Usually aluminum alloys are used bearings to hard disk drive in computer. In order to apply aluminum alloys to bearing used in hard disk drive, this paper presents the characteristics of Micro ECM for aluminum alloy.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.214-217
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• 2002

Micro Surface Electrochemical Machining has traditionally been used in highly specialized fields such as those of the aerospace and defense industries. It is now increasingly being applied in other industries where parts with difficult-to-cut material, complex geometry and tribology such as compute. hard disk drive(HDD) are required. Pulse Electrochemical Micro-machining provides an economical and effective method for machining high strength, high tension, heat-resistant materials into complex shapes such as turbine blades of titanium and aluminum alloys. Usually aluminum alloys are used bearings to hard disk drive in computer. In order to apply aluminum alloys to bearing used in hard disk drive, this paper presents the characteristics of Micro Surface Electrochemical machining for aluminum alloy.

• KIEAE Journal
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• 제11권4호
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• pp.95-101
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• 2011

Earth has been used as a building material not only our country but also many foreign countries in the world. In foreign countries, we can often find the high-storied earthen houses which have been maintained for over several hundred years, which means the fact that earth differs in durability according to the methods of utilizing earth. So, the purpose of this study is to progress the fundamental research for utilizing earth as a wall material. Also, the another purpose of this study is to utilize the optimum micro-filler effect which adjusts the grain size of earth and the lime composite which promotes chemical combining power, and so examine whether earth material ensures its high compressive strength. This study applied both of rammed earth method and pour earth method among earth architecture methods. This study investigated compressive strength, slump, and air content according to unit binder weight. On the basis of such experimental results, this study derived the following conclusions. 1) Optimum micro-filler mixtures reduce a lot of fine particles contained in earth. If optimum micro-filler mixtures are used as aggregates, they develop lower W/B and relatively higher strength than general earth. 2) In this study, which uses optimum micro-filler earth mixtures and lime composite, rammed earth method develops 29MPa and pour earth method develops 28MPa in 28 days compressive strength. Such strengths can be utilized in building walls.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.692-697
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• 2004

This study is on the increasement of strength about soft ground improvement material using waste residual(paper fly ash, coke ash, slag) by fire. Through this study the authors have analyzed the strength improvement of mixed soft silty sand with improvement materials. The strength of mixed soils with high mixture ratio and more curing days increased. But CA-30(cokes 60%) make more low strength improvement than others. Therefore the authors find out that paper fly ash+cokes, paper fly ash+slag or cokes+slag improvement material is more effect in improvement of soft silty sand than cokes+cenlent. And Ettringite reaction is free mixed soils with more than two materials.

• 대한치과보철학회지
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• 제37권3호
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• pp.313-327
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• 1999

The aim of this study was to compare wear resistance of resin denture teeth opposing various restorative materials. The wear resistance of conventional acrylic resin teeth(Trubyte Biotone) and three high-strength resin teeth(Bioform IPN, Endura, SR-Orthosit-PE) opposing different restorative materials(gold alloys, dental porcelain, composite resin) was compared. Wear tests were conducted with a sliding-induced wear testing apparatus which applied 100,000 strokes to the specimen in a mesio-distal direction under conditions of 100 stroke/min and constant loading of 1Kgf/tooth. Wear resistance of the resin denture teeth was evaluated by the following criteria : 1) wear depth, 2) weight loss, and 3) SEM observation. Results were as follows. 1. When opposed to gold alloys and composite resin, high-strength resin teeth showed superior wear resistance compared to acrylic resin teeth. But, in cases opposing dental porcelain, differences between the wear of the high-strength and acrylic resin teeth were not statistically significant (p<0.05). 2. When comparing wear resistance among high-strength resin teeth, opposing gold alloys, Endura was slightly more resistant and while in cases opposing dental porcelain, SR-Orthosit-PE was showed to be slightly resistant(p<0.05). 3. The wear of high-strength resin teeth was greater by 5 to 7 times when opposing porcelain and 2 to 3 times when opposing composite resin compared to gold alloys(p<0.05). 4. SEM observations of the wear surface showed that wear of resin teeth opposing gold alloys is a fatigue type of wear and wear of resin teeth opposing dental porcelain is fatigue and abrasion type of wear. Trubyte Biotone showed more severe fatigue type of wear than high-strength resin teeth. In conclusion, the use of dental porcelain should seriously be considered as restorative material in cases opposing resin denture teeth and improvement seems to be needed on resin teeth in the areas of wear resistance.

• 콘크리트학회논문집
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• 제11권5호
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• pp.119-130
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• 1999

Recently, as the building structure has been larger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. From the test result, High-strength concrete with cylinder strength of 1,200kgf/$\textrm{cm}^2$ in 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns and fracture modes. The load versus strain and load versus deflection relations were obtained from the static test. The relation of cycle loading to deflections on the mid-span, the crack propagation and the modes of failure according to cycle number, fatigue life and S-N curve were observed through the fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed to 57~66 percent of the static ultimate strength. Fatigue strength about two million cycles from S-N curves was certified by 60 percent of static ultimate strength.

• KIEAE Journal
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• 제12권5호
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• pp.93-98
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• 2012

The headed studs those are used extensively for steel-composite construction is specified as SS400 at the current Korean Standard specification considering the welding condition. And the corresponding equation for the shear force calculation is limited for the use of compression strength of concrete below $300kg/cm^2$. However, it is expected that the high strengthening and precast of both steel and concrete due to the necessity of shear connector or other connecting material for the combination of steel and concrete. Therefore, the experimental results obtained during the development process of high strength stud for the connection of high strength concrete and the steel member are reported in this paper. Also the effectiveness of newly developed shear connector using pipe to increase the stiffness of a stud is verified by comparing both the stiffness and the strength with common stud bolt through the welding ability, mechanical characteristics and experimental investigation.