Han Seung Lee

Analysis of Chloride Diffusion in Cracked Concrete

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.

Prediction of the Carbonation Depth of Concrete with a Mortar Finish

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.

Anti-Corrosion Performance of Zn-Al Thermal Metal Spraying Method Using Steel Structures

This study performs an electrochemical experiment to quantitatively evaluate the corrosion resistance performance in a Zn-Al thermal metal spraying method and produces corrosion current density according to the type of corrosion resistance methods. In the results of the calculation, the corrosion membrane produced in a Zn-Al thermal metal spraying method showed voltage differences more than 300 mV and that demonstrated enough corrosion performance with the corrosion resistance reaction of base materials and proper Zn-Al ratio, such as 50:50. Also, the results exhibited that the corrosion speed in a Zn-Al thermal metal spraying method was 0.66 time faster than that of the zinc galvanizing method in the estimation based on the standard of corrosion resistance service years in a zinc galvanizing method (JIS H 8641).

Prediction of the Elastic Modulus of Cement Paste as a Kinetic Hydration Model

This paper describes a numerical method for estimating the elastic modulus of cement paste. The cement paste is modeled as a unit cell, which consists of three parts: dehydrated cement grain, gel, and capillary pore. In the unit cell, the volume fractions of the constituents are quantified with a single kinetic function of the degree of hydration. The elastic modulus of cement paste was calculated from the total displacement of constituents when the uniform pressure was applied to the gel contact area in cement paste assumed a homogenous isotropic matrix. Numerical simulations were conducted through the finite element analysis of the three-dimensional periodic unit cell. The model predictions were compared with experimental results. The predicted trends agree with experimental observations. The approach and some of the results might also be relevant for other technical applications.

An Experimental Study on the Development of Structural Lightweight Concrete Using Micro Foam Agents

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.

Study on an FEM Analysis to Evaluate Restrain-Performance of Surface-Finishes for Carbonation

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.

Analysis of Chloride Penetration into the Corner Zone of Concrete Structure Member

Chloride penetration into concrete is the main cause of steel corrosion in concrete structures exposed to chloride-rich environments. In general, conditions on the diffusion process are dominant among various penetration mechanisms, such as ionic diffusion, capillary sorption, and so on. In recent analysis of current literature, chloride diffusion is as a simplified one-dimensional diffusion process. However, for the rebar in the corner zone of concrete beam, the diffusion belongs to a two-dimensional diffusion. Based on a galerkin finite element method, a two-dimensional diffusion differential equation is built and solved numerically and the different chloride concentration is compared to one dimensional diffusion and two-dimensional diffusion process. The service life of concrete structure members under two-dimensional chloride penetration is predicted by compared with a critical threshold chloride concentration. Compared with general one-dimensional chloride attack, the service life is considerably reduced in a corner zone due to two-dimension penetration.

A Study on the Evaluation of Probabilistic Durability Life for RC Structures Deteriorated by Chloride Ion

Chloride attacks concrete structures becoming a primary factor that deteriorates the durability of concrete structures. For this reason, research has been conducted on chloride ion penetration and diffusion. This research produced an accurate durability life prediction through reliability assessments and proposes a prediction method for the chloride ion diffusion coefficient of a concrete applied assessment program for reliability. As a result, test materials were fabricated using different admixtures and chloride ion diffusion coefficient was calculated by applying an RCPT test at each equivalent age. Based on these results, reliability prediction formulas were indicated through the reliability analysis for a durability life design using a Montecarlo method. In addition, propriety was verified through comparisons and analysis using the proposed formula with the investigated data for chloride ion diffusion.

Apparent Activation Energy for Predicting Compressive Strength of Concrete Using Blast Furnace Slag

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 (Ea) 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%, Ea 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.

Numerical Simulation of Heat Evolution of Eco-Friendly Blended Portland Cements Using a Multi-Component Hydration Model

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.