Keun Hyeok Yang

Long-Term Behavior of Low-Heat Cement Concrete under Different Curing Temperatures

The present study is to estimate long-term characteristics of low-heat cement-based ternary blended concrete prepared for reducing hydration heat in mass concrete. 15% modified fly ash and 5% limestone powder were added for partial replacement of the low-heat cement. To achieve the designed compressive strength of 42 MPa, water-to-binder ratios were determined to be 27.5, 30 and 32.5% for ambient curing temperatures of 5, 20 and 40°C, respectively. Test results showed that, with the decrease in curing temperature, the drying shrinkage strains tended to decrease, whereas creep strain increased.

Effect of Concrete Types and Construction Joints on Concrete Shear Friction Characteristics

The present study examined the effect of smooth construction joint and concrete unit weight on the shear friction behavior of concrete. From nine push-off test specimens, shear load-relative slip relationships, shear cracking stress, shear friction strength were measured. Test results showed that the shear cracking stress was hardly affected by the configuration of transverse reinforcement or concrete unit weight. The shear friction strength of monolithic normal-weight concrete was approximately three times higher than that of the companion specimens with construction joint. Meanwhile, the heavyweight concrete joints had a similar shear friction strength to normal-weight concrete ones.

The Development of Concrete Life Cycle Assessment System

In the present study, a concrete life-cycle assessment system (CLAS) is developed that can easily and quantitatively assess green-house gas emissions during the production of concrete by applying life-cycle assessment techniques. The CLAS is divided into simple and detailed assessment methods; a database (DB) of a standard mix design and energy consumption amount, and basic green-house units applicable to each method, was constructed. A case assessment using the developed system showed that the green-house gas emission determined by the detailed assessment method differed from that by the simple assessment method by approximately 10%. These results show that the proposed method is suitable for estimating green-house gas emissions related to concrete.

Effect of Corrosion Inhibitor on the Compressive Strength of Polymer-Modified Cement Mortars

This study examined initial flow and compressive strength development of polymer-modified cement mortar according to the addition of corrosion inhibitor. Test results showed that with the increase of the amount of corrosion inhibitor, the initial flow of mortars increased whereas compressive strength decreased. The strength development of mortar specimens could be reasonably predicted using the modified ACI 209 equations.

Effect of Unit Binder Content on Mechanical Properties of Foamed Concrete

The present study tested six concrete mixes to develop a high-performance foamed concrete without using high-pressure steam curing processes, as an alternative to autoclaved aerated concrete (AAC) blocks. Dry density, compressive strength and thermal conductivity of foamed concrete were measured according to the variation of unit binder content. Test result showed that dry denstiy, compressive strength and thermal conductivity of foamed concrete incresed with the increase in the unit binder content. The compressive strength of tested foamed concrete was commonly higher than that of conventional foamed concrete with the same dry density.

Effect of Fly Ash on LifeCycle CO2 Assessment of Concrete Structure

The objective of the present study is to ascertain the effect of fly ash (FA) on the lifecycle CO2 assessment of reinforced concrete structures. The reliable lifecycle CO2 assessment approach of concrete structures were established and then specified using the developed CO2 a performance evaluation table. The system boundary studied was from cradle to recycling of concrete, which includes material system, concrete production, transportation, construction, use and recycling activity phases. The assumed time and regional boundaries for concrete mixes were 2012 and Seoul, South Korea, respectively. The carbonation depth of concrete and CO2 uptake during use of structure and recycling phases were calculated based on the Yang et al.’s model. Using the performance evaluation table, the effect of FA on the lifecycle CO2 assessment of concrete columns and beams in an office building was examined under the different concrete strengths. The parametric study clearly showed that high-strength concrete is favorable to the reduction of lifecycle CO2 amount of concrete columns, whereas the reduction is not expected for concrete beams. The lifecycle CO2 amount of concrete structures decreases with the increase in the substitution level of FA up to 20%, beyond which the decreasing rate is insignificant.

Compressive Strength Development of High-Strength Concrete under Different Curing Temperatures

The present study examined the in-place strength of high-strength concrete based on the relative strength-maturity relationship. The measured strength gain of high-strength concrete was compared with the predictions obtained from the modified maturity function to consider the offset maturity and the insignificance of subsequent curing temperature after an age of 3 days on later strength of concrete. This study demonstrates that the compressive strength gain of concrete cured at the reference temperature (20°C) for an early age of 3 days is little affected by the subsequent curing temperature histories.

Shrinkage Model for Heavyweight Concrete Using Magnetite Particles

The CEB-FIP equations generally underestimate the shrinkage strains of heavyweight concrete, showing a more notable trend with the increase in ages and equivalent porosities of aggregate. This study formulated the shrinkage behavior of heavyweight magnetite concrete as an expanded version of GL 2000 model by introducing the parameter of an equivalent porosity of aggregates. The proposed models gave significantly more accurate predictions than CEB-FIP equations even at long-term ages.

Assessment on Physical Properties and Environmental Load Emission of Concrete Using Early Strength Activator Blast Furnace Slag

In relation to global warming, there is a need for development of alternative material to reduce cement use by concrete. Accordingly in this study, A-BFS (Activator Blast Furnace Slag) mixed with an activator composed of industrial wastes such as wastewater sludge and sewage sludge was developed. Physical property for compressive strength development was tested on concrete mixed with the developed A-BFS. In addition, environmental load (CO2) emission and reduction performance were analyzed on concrete mixed with A-BFS.