Papers by Author: Han Seung Lee

Abstract: Concrete with blast furnace slag (BFS) shows varied strength development properties under general temperature conditions. Therefore, a precise prediction of compressive strength using a full maturity model is desired. The purpose of this study is to predict the compressive strength of concrete with BFS by calculating the apparent activation energy (E_a) for each BFS replacement ratio, applying this activation energy to the equivalent age model, and then using the Carino model. For BFS replacement ratios of 0%, 10%, 30%, and 50%, E_a is calculated as 33.475 kJ/mol, 37.325 kJ/mol, 41.958 kJ/mol and 45.541 kJ/mol respectively. Finally, the compressive strength of concrete with BFS is predicted.

Abstract: The various methods for improving chloride penetration resistance in the reinforced concrete have been developed. Among the related general ways, using of corrosion inhibitor became very common. Therefore, in this study, in order to comprehend performance of corrosion inhibitor, the experiment study was conducted about corrosion characteristic of 3 steps(0.0, norm 1/2, norm) compared to organic corrosion inhibitor standard use of liquid and molar 3 steps(0.0, 0.3, 0.6%) of Chloride by added amount of inorganic corrosion inhibitor by the corrosion inhibitor types about 2.4kg/m³, 4.8kg/m³ based on Chloride ion content 1.2kg/m³ for service life prediction of concrete structure by using Poteniostat. As results, in the case of inorganic nitrous acid corrosion inhibitor, it was confirmed that anti-corrosive performance of Chloride ion content 1.2kg/m³ by corrosion Ecorr -0.30V in more than molar ratio 0.3%, and it also was confirmed that anti-corrosive performance of 2.4kg/m³, 4.8kg/m³ in more than molar ratio 0.6%. In addition, the excellent anti-corrosive performance of organic corrosion inhibitor was shown in 1/2(0.42kg/m³) of norm regardless of Chloride ion content, and it can be seen that absorption types organic corrosion inhibitor has excellent anti-corrosive performance compared to the inorganic nitrous acid corrosion inhibitor by the added amount of corrosion inhibitor.

Abstract: Corrosion sensors were devised to develop a system whereby the depth of chloride permeation from concrete surfaces can be monitored in cover concrete of reinforced concrete structures. For making sensor which is similar to rebar author uses Screen printer machines, Ag paste and Fe powder. Appropriate portion of Ag and Fe is over 1:2. The resistance of sensors increased as the degree of corrosion increased.

Abstract: Concrete is a type of porous materials and is physically and chemically damaged due to exposure to various environments from the placing to the service life. These reactions affect the corrosion of steel bars applied in concrete and that decreases the durability life and strength of such steel bars. Thus, it is very important to insert rust inhibitors into steel bars in the case of a deterioration element that exceeds the critical amount of corrosion in the location of steel bars. However, it is very difficult to guarantee corrosion resistance at the location of steel bars using conventional technology that applies corrosion inhibitors only on the surface of concrete. This study attempts to develop a method that penetrates corrosion inhibitors up to the location of steel bars and investigate the penetration depth of corrosion inhibitors by verifying moisture migration in concrete under an applied pressure.

Abstract: When the RC structure degraded in sea environment, chloride ion is one of the most important factors of degradation. Therefore, the purpose of this analytical study is measuring diffusion coefficient of patching repair material and the structure which repaired with patching repair material by RCPT. Also with this experimental result, Finite Element Method (FEM) is used for determining service year of building and concentration of chloride ion in the structure material. As the result of RCPT, diffusion coefficient of patching repair material is 0.44×10-8cm2/sec, which is 18.7% of concrete (3.18×10-8cm2/sec). Meanwhile, as the result of FEM, patching repair material is effective for prevent chloride ion. When service year of normal concrete structure is 16years, on the other hand, the structure recovered 10mm of patching repair material will take 49 years to its service year. Furthermore, the result derived from equation given from JSCE predicts service year of the structure is little bit less than FEM.

Abstract: Cathodic Protection Method was introduced as a corrosion protection method of metals under the ground or sea. Since 1970, it was applied to corrosion protection method of reinforced concrete structures. After 1990, this method has been used around the world, and its usability was proved. But this method has some problems on the aspect of construction and economy. In order to solve these problems, Cathodic Protection Method by using high durable metal spray was developed. First, the specimen was covered with anodic materials (Zn, Al) by using metal spray. And a performance of corrosion protection was confirmed by measuring corrosion current and halfcell potential of specimen. Through the result of experiment, it is possible to know that Cathodic Protection Method by using high metal spray is good protect to corrosion on reinforced concrete structures.

Abstract: This paper presents a model for chloride diffusion in cracked concrete. This numerical model includes two parts: hydration model and chloride diffusion model. The hydration model starts with mix proportion of concrete and considers both Portland cement hydration and pozzolanic activity. By hydration model, the evolution of properties of cement paste is described as function of curing age. Furthermore, based on general effective media theory and composite spheres assemblage model, the effective diffusivity of chloride ions in concrete without crack is obtained. Finally based on crack distribution in cracked concrete and finite element methods, the diffusion of chloride ions in cracked concrete is predicted. The prediction results agree well with experiment results.

Abstract: It is well known that carbonation will result corrosion of steel reinforcement in reinforced concrete structures. To reduce the rate of carbonation, the surface coatings, such as mortar finish, has been used widely to concrete. This paper presents a numerical procedure about carbonation of the coating-concrete system. This numerical procedure starts with a multi-component hydration model. By hydration model which considers both and Portland cement and pozzolanic reaction, the amount of hydration products which are susceptible to carbonate as well as porosity is obtained as function of age. Furthermore, the diffusivity of CO2 is determined and carbonation depth of concrete is predicted. Parameter studies are performed to show the influence of composition and application time of mortar finish on carbonation depth of substrate concrete.

Abstract: Autogenous shrinkage is the term for the bulk deformation of a closed, isothermal, cement-based material system not subjected to external forces. It is associated with the internal volume reduction of cement/water mixture in the course of the hydration process. However, addition of blended components to cement, especially such as fly ash or silica fume, for the high-performance concrete 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, numerical simulation is suggested to predict autogenous shrinkage of high performance cement paste. The simulation is originated from a multicomponent hydration model. 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: Life span of structures made with concrete was shortened by carbonation. This phenomenon makes pH in concrete lower. If pH value in concrete become below 10, rebar in concrete begin to be corroded. This pH value was effected by quantity of Ca(OH)2 that depends on cement types, hydration reaction and carbonation time. In this study, pH value and quantity of Ca(OH)2 in mortar which has blast furnace slag were tested according to hydration and carbonation time. As a test result, the more cement has blast furnace slag (BFS) and the longer carbonation time last, the lower pH value in mortar has. And using this quantitative analysis result of pH and Ca(OH)2, it may be used effectively when service life considering carbonation is predicted using FEMA.