• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.349-354
• /
• 1999

Specialty cellulose fibers processed for the reinforcement of concrete offer relatively high levels of elastic modulus and bond strength. The hydrophilic surfaces of specialty cellulose fibers facilitate their dispersion and bonding in concrete. Specialty cellulose fibers have small effective diameters which are comparable to the cement particle size, and thus promote close packing and development of dense bulk and interface microstructure in the matrix. The relatively high surface area and the close spacing of specialty cellulose fibers when combined with their desirable mechanical characteristic make them quite effective in the suppression and stabilization of microcracks in the concrete matrix. The properties of fresh mixed specialty cellulose fiber reinforced concrete and the contribution of specialty cellulose fiber to the restrained shrinkage crack reduction potential of cement composites at early age and theirs evaluation are presented in this paper. Results indicated that specialty cellulose fiber reinforcement showed an ability to reduce the total area significantly (as compared to plain concrete and polypropylene fiber reinforced concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.551-554
• /
• 2005

The durability of concrete is decreased by various deterioration factors such as a crack, spalling, corrosion. Many repair and rehabilitation methods have been introduced to extend service life of RC structure. An application of coating material is one of repair and rehabilitation methods. However, there is a problem due to reduction of bonding strength and damage of coating material in the case of existed coating material. Thus, this paper is aim to investigate the chloride resistance according to application method of coating material which improve the existed problem. According to the results, it is showed that application of coating material reduces diffusion of chloride into concrete. In special, application of MMA polymer showed the best resistance for chloride attack. However, variation of application method and number of times has a minor effect on chloride diffusion.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.609-614
• /
• 2000

This paper is an experimental study of the normal strength concrete beam and high strength concrete beam for the analysis of bending and shear behavior. In building structure, the story height can be minimized by providing openings in beams which serves for the utility equipments passing through. The dead space in false ceiling increase construction cost, the good ceiling system such as beam with opening give to economical merits because of a substantial reduction in materials and construction cost. For the analysis on the mechanical behavior of the reinforced high strength and normal strength concrete beams with circular opening in the web, the stress concentration of the circular opening, crack pattern and reinforcing methods were studied. Twenty test pieces with different reinforcing methods and difference concrete strength were tested and their resisting forces and load deflection curves were defined in this study.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.473-476
• /
• 2003

This study discusses the use of anti-shrinkage agent as the method to reduce autogenous and drying shrinkage. According to results, as for the fundamental properties of high performance concrete, fluidity and strength decrease with an increase of the adding ratio of anti-shrinkage agent, but air content increases. Compared with plain concrete, autogenous and drying shrinkage are reduced by 12~52% and 4~22% respectively upto the adding rario of anti-shrinkage agent of 2.0%. When expansive additive is added by 5.0%, they are also reduced by 38~95% and 15~50% respectively. Therefore, as expansive additive of 5.0% and anti-shrinkage agent of 1.0% are added to high performance concrete of around W/B 30%, it is considered that fluidity and strength are hardly influenced, and in addition, crack by shrinkage can be prevented effectively.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.27-30
• /
• 2003

This study is investigated the various properties and drying shrinkage of concrete according to water content under the condition proper fluidity is adjusted, in order to suggest the method for reduction of crack by drying shrinkage. According to the results, though water content varies, slump and air content are satisfied to the planed values, but shear slump and separation happen at water content of 120 and 140kg/$m^3$ due to the overuse of superplasticizer(SP). As water content is diminished, setting time is retarded by an increase of the using amount of SP, and compressive and tensile strength increase in the range of 160-180kg/㎥ of water content, but decrease significantly at 120 and 140kg/$m^3$. Length change by drying shrinkage decrease with a decrease of water content. Therefore, considering not only drying shrinkage but also fluidity, setting time and strength, it proves that the most appropriate water content of concrete is 160kg/$m^3$ in the condition of this experiment.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.265-266
• /
• 2010

In this study, reduction of the crack in the lean concrete for pavements by combining different types of fibers is discussed to compare and verify its validities. Experimental result using NY fibers is depending on excellent aspect ratio and hydrophilic. Vebe time has shown good results. In addition, the addition of PP fiber had most favorable flexural strength.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.371-372
• /
• 2010

This study was a result of mock-up test for the field application which was compared between low heat cement and temperature-reducing binder with the way of temperature crack reduction. The result of mock-up test was shown that the heat of hydration from the low heat cement and the temperature-reducing binder indicated 44 and $54^{\circ}C$ respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.416-420
• /
• 2004

Recently, the importance of vibration reduction at the local structure such as tank, deck which attached machinery and compass deck, has continuously increased by owner and shipbuilder. Because crews are afflicted with them and severe vibration problems affect on the crack of structure. This study conducted optimum design to get a stiffener size of local structure to reducing the vibration level and dec leasing the weight of structure in ship. Random tabu search method (R-Tabu) has fast converging time and can search variables size domains for nonlinear problems. This paper used Nastran external call type independence optimization method which makes using a solver module from Nastran.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.878-883
• /
• 2003

To modify some problems of ACI shear provisions, ultimate shear strength equation considering size effect and arch action to compute shear strength in high-strength concrete beams without stirrups is presented in this research. Three basic equations, namely size reduction factor, rho factor, and arch action factor, are derived from crack band model of fracture mechanics, analysis of previous some shear equations for longitudinal reinforcement ratio, and concrete strut described as linear function in deep beams. Constants of basic equations are determined using statistical analysis of previous shear testing data. To verify proposed shear equation for each variable, namely d, , ρ, f/sub c/' and aid, about 250 experimental data are used and proposed shear equation is compared with ACI 318-99 code, CEB-FIP Model code, Kim & Park's equation and Zsutty's equation. While proposed shear equation is simpler than other shear equations, it is shown to be economical predictions and reasonable safety margin. Hence proposed shear strength equation is expected to be applied to practice shear design.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.7 no.4
• /
• pp.44-49
• /
• 2008

The characteristic of magnesium alloy is the most light in utility metal, the effect of electromagnetic wave interception, excellent specific strength and absorptiveness of vibration. Although magnesium alloy with above characteristic is a subject matter which is suitable in world-wide tendency of electrical component frame, sheet magnesium alloy is difficult to process. Therefore, forming analysis of sheet magnesium alloy and applying warm-working to process are indispensable. Among Finite element method, the static implicit finite element method is applied effectively to analyze sheet magnesium alloy stamping process, which include the forming stage. In this study, it was focused on the crack, wrinkling and spring back on sheet magnesium alloy stamping by the static implicit analysis. According to this study, the result of simulation will give engineers good information to access the forming technique on sheet magnesium alloy. And its application is being increased especially in the production of electrical component frame for the cost reduction, saving of defective ratio, and improvement of Productivity.