Joong-Kyu Jeon

A Study on the Penetration Resistance and Spalling Properties of High Strength Concrete by Impact of High Velocity Projectile

Concrete materials subjected to impact by high velocity projectiles exhibit responses that differ from those when they are under static loading. Projectiles generate localized effects characterized by penetration of front, spalling of rear and perforation as well as more widespread crack propagation. The magnitude of damage depends on a variety of factors such as material properties of the projectile, impact velocity, the mass and geometry as well as the material properties of concrete specimen size and thickness, reinforcement materials type and method of the concrete target. In this study, penetration depth of front, spalling thickness of rear and effect of spalling suppression of concrete by fiber reinforcement was evaluated according to compressive strength of concrete. As a result, it was similar to results of the modified NDRC formula and US ACE formula that the more compressive strength is increased, the penetration depth of front is suppressed. On the other hand, the increase in compressive strength of concrete does not affect spalling of rear suppression. Spalling of rear is controlled by the increase of flexural, tensile strength and deformation capacity.

Fundamental Evaluation and Hydration Heat Analysis of Low Heat Concrete with Premixed Cement

(Received February 11, 2014 / Revised March 19, 2014 / Accepted March 24, 2014)This study carried out to evaluate the hydration heat analysis and fundamental characteristics such as air content, slump, compressive strength and dry shrinkage according to concrete with premixed cement, ternary concrete and OPC concrete for using concrete wit hpremixed cement. The results of experiment are founded that concrete with premixed cement have sufficient performances such as workability, compressive strength and dry shrinkage. Also, the results of hydration heat analysis are founded that concrete with premixed cement have more performance than ternary concrete and OPC concrete at a point of view for the quality control such as thermal crack reducing and economic benefit. Therefore, it is desirable that concrete with premixed cement should be used to rise durability performance and convenience of maintenance.키워드 : 혼합 시멘트, 기초물성, 수화열 해석, 현장적용Keywords : Premixed cement, Fundamental characteristics, Hydration heat analysis, Field application* Corresponding author E-mail: jkjeon31@kolon.com

Durability Evaluation of Tunnel Lining Concrete Reinforced with Nylon Fiber

Tunnel structures are widely used for transportations in mountains areas. To shorten the construction period and to cut down the construction expenditure, a construction technique that a tunnel excavation process and a tunnel lining process are simultaneously performed is often applied in the field. However, due to the vibration and impact caused by excavation process, cracking and deterioration of tunnel lining concrete could happen. This research experimentally investigated the effective role of the usages of blended cement and recently developed nylon fibers for tunnel lining concrete. It has been observed that both nylon fibers and blended cement improve the durability and physical properties of concrete.

Service Life Prediction of Concrete Structures Exposed to a Sulfuric Acid Environment

In this study, it was investigated the resistance of OPC, 60% GGBS, 20% PFA and 10% SF mortar specimens against sulfuric acid corrosion. As an index for degree of acid corrosion, the corrosion depth was evaluated. Then, it was found that an increase in the duration of immersion and a decrease in the pH, as expected, resulted in a more severe corrosion irrespective of binders; 60% GGBS mortar specimen was the most resistant to sulfuric acid corrosion. From the laboratory testing of sulfuric acid corrosion, an empirical prediction model was suggested as a power function of time and the pH of sulfuric acid, and was applied to an assessment of concrete structures exposed to an acidic environment. It was found that the empirical model gave a more precise prediction of sulfuric acid deterioration of concrete rather than a conventional model, mostly used for predicting carbonation of concrete.

Study on Hydration Heat Analysis of Pier Foundation-Column Using Low Heat Concrete

(Received September 12, 2014 / Revised September 22, 2014 / Accepted September 25, 2014)This study carried out to evaluate the hydration heat analysis and fundamental characteristics such as air content, slump and compressive strength for field application of low heat concrete with premixed cement. The results of experiment show that low heatconcrete with premixed cement have sufficient performances on the workability and compressive strength. In addition, hydration heat analysis shows that low heat concrete with premixed cement make sure of target thermal cracking index. Therefore, it is desirable to apply the low heat concrete with premixed cement on pier foundation-column.키워드 : 저발열 콘크리트, 혼합시멘트, 수화열 해석, 온도균열지수Keywords : Low heat concrete, Premixed cement, Hydration heat analysis, Thermal cracking index* Corresponding author E-mail: ksg85@kolon.com