Papers by Author: Han Seung Lee

Abstract: Examination about sticking intensity security way of normal temperature metal spraying covering is required compulsorily accordingly with quantitative assessment about steel plate's surface roughness to secure adhesive power of steel materials and metal membrane stably at application of way method of construction by normal temperature metal spraying. In case of metal spraying, Sticking strength of metal spraying way finish is influenced greatly, and it is judged that is desirable that manages Sm/Rz by 6 lows to secure more than sticking intensity 20kgf/cm2 by Sm/Rz that evaluate that is rough of nature surface. The purpose of this study was to analyze an adhesion strength of metal spraying finish layer with the surface conditions of steel plate. For the purpose the experimental factors such as anticorrosive finish method and surface treatment method were selected.

Abstract: The purpose of this research is to evaluate the effectiveness of nitrate as a corrosion inhibitor in mortar containing chloride. In the experiment, test specimens of mortar to which chloride and nitrite had been added, were subjected to accelerated corrosion by means of repeated drying and wetting on condition of high temperature. This study concerns the assessment of the inhibition effect of nitrite-based corrosion inhibitor using a polarization method and its influence on the chloride transport, compressive strength and setting time of concrete. From the results of the experiments, it was confirmed that the lithium, calcium nitrite corrosion inhibitor and new corrosion inhibitor over dosage 0.6 (NO2-/Cl-) molar ratio is very effective in protecting reinforcement from corrosion in mortar in which chloride ions have contained.

Abstract: Where the self weight of the overall slab needs to be considered, the quantity of in-situ concrete required can be reduced by the introduction of polystyrene void forms supplied and fixed to the precast panel during manufacture. In this study, new I-slab system with polystyrene form and precast concrete deck is proposed to reduce the construction period and the self weight of the slab. This paper presents experimental works on the bending and shear of the I-slabs. Five specimens were tested. The main parameters of experiments were the hole diameter of polystyrene form and the thickness of slab. Structural performance of I-slab was evaluated on the basis of failure mode, load-displacement curve, and ultimate strengths. Based on the test results, the critical punching shear sections were changed as test variables, so the punching shear strengths were very different. Test results indicated that the developed I-slab were very effective to increase the strength because of self weight reduction.

Abstract: Fly ash and granulated blast-furnace slag, which are used as blends of Portland cement, are waste materials produced in electric and energy industry. Due to excellent durability, low heat of hydration, energy-saving, resource-conserving, and generally less expensive than ordinary Portland cement, blends Portland cements is used increasingly in construction industry. Both ecology benefit and economic benefit can be achieved by using blended Portland cement. Addition of blended components to cement, especially such as fly ash or silica fume, will lead to a densification of the microstructure. The autogenous shrinkage deformation will increase and the following autogenous shrinkage crack will do harm to durability of concrete structure. In this paper, based on the multi-component hydration model, a numerical program is built to predict autogenous shrinkage of ordinary Portland cement and blended Portland cement. The numerical program considers the influence of water to cement ratio, curing temperature, particle size distribution, cement mineral components on hydration process and autogenous shrinkage. The prediction result agrees well with experiment result.

Abstract: With the development of concrete industry, the necessity for utilizing waste materials and decreasing overall energy consumption is becoming increasingly obvious. Fly ash and granulated blast-furnace slag, which are used as blends of Portland cement, are waste materials produced in electric and energy industry, and concretes made with them can have properties similar to ones made with pure Portland cement at lower cost per unit volume. By using blended Portland cement, both ecology benefit and economic benefit can be achieved. Due to the pozzolanic reaction between calcium hydroxide and blended components, compared with ordinary Portland cement, hydration process of blended Portland cement is more complex. In this paper, based on a multi-component hydration model, a numerical model which can simulate heat evolution process of blended Portland cements is built. The influence of water to cement ratio, curing temperature, particle size distribution of cement paste and blended Portland material, and cement mineral components on heat evolution process is considered. The prediction result agrees well with experiment result.

Abstract: A cement which is used in construction and a concrete which is a hydration product of cement is considered anti-environmental materials because of lots of CO2 emission in progress of producing and making them. But a concrete absorbs CO2 gas in atmosphere after hydration and in its lifetime. It is called carbonation. Based on Papadakis’ theses, this research is carried on calculation of the CO2 absorption quantity in concrete. After research, we calculated the CO2 absorption quantity in concrete which has various surface-finishes and we evaluate each surface-finishes the resistance against carbonation.

Abstract: In this study, accelerated corrosion tests were conducted on concrete specimens with and without accelerated carbonation beforehand for the purpose of elucidating the effects of carbonation, cover depth, and water-cement ratio (W/C) on the reinforcement corrosion. During testing, the corrosion current between the anode steel and cathode stainless steel was measured to continuously monitor the progress of corrosion throughout the test period, thereby investigating the mechanism of reinforcement corrosion and the relationship between corrosion and crack width, as well as other parameters.

Abstract: Recently, Reinforced Concrete(RC) is used in most buildings. However, steel bars in concrete cause corrosion through carbonation. Furthermore, corrosion shortens the life span of RC structures. Therefore, the surface-finishes such as restraint for penetration and diffusion of CO2 were used to lengthen the life span of RC structures. This study attempted to verify the restraining effect on a carbonation job according to the applied surface-finishes using an FEM analysis. This study also evaluated the restraining effect of carbonation on other surface-finishes with the process proposed in this study.

Abstract: It is well known that PC (polycarboxylate) agent is superior to other agents for the early-strength of concrete. Thus, this study investigates the development of mortar strength using various agents. To prove this, various factors were tested. Furthermore, this study measured compressive strength at the age of 18, 24, 36, 72, and 168 hours and gave a request text TG/DTA to observe minute structures. In addition, this study took pictures of minute structures using an SEM for each agent at the same age. According to the results, mortar using an early-strength PC agents is faster than a general water reducing AE agent, high performance PC agents, and other agents in the acceleration of hydration at the same early age. A TG/DTA test shows that the early-strength PC agents create more hydration products, such as Ca(OH)2, than others at the same age. The degree of pH in each agent is unrelated to the degree of hydration in mortar. An MIP analysis confirms these results. However, other methods are required the exact analysis of micro structures.

Abstract: The purpose of this study is to obtain basic data on the properties of the development of lightweight concrete containing a foam agent for various applications. This experiment confirmed that compressive strength increased specific gravity, by changing the foam agent into a variable and measuring the compressive strength of concrete.