Yun-Wang Choi

Flowability and Strength Properties of High Flowing Self-Compacting Concrete Using for Tunnel Lining

So far, there has been no study of the concrete to strengthen in the lining of the tunnels, except for the study of the stability of subgrade and the tunnel construction technologies. In the existing concrete work for tunnel lining, lots of problems happen due to the partial compaction and the material segregation after casting concrete. Accordingly, the aim of this study is to improve economic efficiency and secure durability through the improvement of the construction performance and quality of the concrete for the tunnel lining among the civil structures. Therefore, the compactability and strength properties of the High Flowing Self-Compacting Lining Concrete (HSLC) are evaluated to develop the mixing proportion for design construction technology of HSLC that can overcome the inner cavity due to the reduced flowability and unfilled packing, which has been reported as the problem in the existing lining concrete. The result of the evaluation shows that the ternary mix meets the regulations better than the binary mix. Consequently, it has been judged applicable to the cement for tunnel lining.

The Properties of Strength Development of High Volume Fly Ash Concrete with Reduction of Unit Water Content

(Received February 28, 2014 / Revised March 20, 2014 / Accepted March 25, 2014)In this study, strength development properties of high volume fly ash concrete was evaluated through compressive strength of concrete with reduction of unit water content. And concrete specimens were prepared according to target strength 3 level and variation of unit water content. As a result, the improved fluidity were obtained as a result of the ball bearing action of the spherical, the electrostatic rep ulsion and theparticle size distribution of fly ash particles in case of using more than 50% fly ash. Through this, the mixture of fly ash ha s been shownto reduce the amount of water required in concrete. Also, the early strength of high volume fly ash concrete with reduction of unit water content was improved more about 66% than general concrete mixture.키워드 : 하이볼륨 플라이애시, 조기강도, 단위수량, 강도발현Keywords : High Volume Fly Ash, Early Strength, Unit Water Content, Strength Development* Corresponding author E-mail: crete77@semyung.ac.kr

The Experimental Study on the Fluidity Properties of Mortar Using Basalt Fiber and High Volume Fly Ash

(ReceivedDecember19,2014/RevisedDecember26,2014/AcceptedDecember27,2014)This study was evaluated influence of fluidity properties according to basalt fiber and high volume fly ash in the mortar level , as part ofa basic study for development of fiber reinforced concrete using basalt fiber and high volume fly ash. In the first step, it wa s evaluatedthat fluidity properties of mortar according to replacement ratio 6 level of fly ash(10, 20, 30, 40, 50 and 60mass%) and fluidi ty properties of mortar according to content 5 levels of SP(1.3, 1.5, 1.7, 1.9 and 2.1%) and content 5 levels of VA(0.2, 0.4, 0.6, 0.8 and 1.0%) for dispersion of the basalt fiber, in the second step, it was evaluated that fluidity properties of mortar using High-volume f ly ash (50mass%) on 3 levels of basalt fiber length (6, 20 and 30mm). Results of assessment, if after a fiber mixed, it showed that vi scosity agent is more effective to improve the fluidity and fiber dispersion than superplasticizer, high volume fly ash (50%) applying the mixing,due to three properties of fly ash, showed that the improved fiber dispersibility and flow improvement. 키워드 : 하이볼륨, 플라이애시, 바잘트 섬유, 섬유보강, 유동특성Keywords : High Volume, Fly Ash, Basalt Fiber, Fiber Reinforced, Fluidity Properties* Corresponding author E-mail: crete77@semyung.ac.kr

The Study on Effects of Thermal Aging of Dissimilar Weld Zone in a Primary Reactor Cooling System

In a primary reactor cooling system(RCS), a dissimilar weld zone exists between austenitic-ferritic duplex cast stainless steel(CF8M) in a pipe and low-alloy steel(SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and 330°C, while no effect is observed in SA508 cl.3. An investigation of the effect of thermal aging on the various mechanical properties of the dissimilar weld zone is required. The purpose of the present investigation is to find the effect of thermal aging on the dissimilar weld zone. The specimens are prepared by an artificially accelerated aging technique maintained for 100, 300, 900, 1800 and 3600 hrs at 430°C, respectively. The various mechanical tests for the dissimilar weld zone are performed for virgin and aged specimens.

A Study on the Rheology Properties for Development of Sprayed High Performance Fiber Reinforced Cementitious Composites for Protection and Blast Resistant

(Received August 4, 2014 / Revised August 25, 2014 / Accepted September 10, 2014)This paper was evaluated the rheology properties according to each step of paste, mortar and HPFRCC as a part of the basic study to development of sprayed high performance fiber reinforced cementitious composites(HPFRCC) for protection and blast resistant. Rheology test results in step of paste, in case of GGBFs and FA, it showed that the plastic viscosity and yield stress reduced gradually according to the increase of mixing rate, and in case of SF, the plastic viscosity and yield stress increased radically starting from the mixing rate of 10%. Rheology test results in step of mortar, type of aggregates, it showed that particle shape and grading of aggregate is influence on plastic viscosity and yield stress, and change of volume ratio is influence on plastic viscosity than yield stress. Fluidity and rheology test results in step of HPFRCC, if after a fiber mixed, it showed that viscosity agent is more effective to improve the fluidity and fiber dispersion than superplasticizer.키워드 : 방호 ･방폭, 뿜칠, 고성능, 섬유보강, 레올로지Keywords : Protection and Blast Resistant, Sprayed, High Performance, Fiber Reinforced, Rheology* Corresponding author E-mail: crete77@semyung.ac.kr

A Study on the Relationship between Compressive Strength and Water-Cement Ratio According to Water Reducing Ratio

ABSTRACT In this study, the relationship between compressive strength and water-cement ratio according to water reducing ratio was evaluated, concrete mix was prepared according to 3 level of water reducing ratio (0%, 8% and 16%) and 3 level of water-cem ent ratio (40%, 45% and 50%). In addition, concrete mix was carried out repetition test of three times in order to secure the relia bility. As a result, compressive strength according to water reducing ratio was shown that difference of strength was about 20% occurred, effect of compressive strength according to water reducing ratio was found more than the water-cement ratio. Therefore, reflected the effect of water reducing ratio, relationship equation between new compressive strength and water-cement ratio was proposed. Keywords : water reducing ratio, compressive strength, water-cement ratio, concrete, relationship formula 1. 서 론 1) 건설산업은 60년대 이후 급속한 산업화 정책과 더불어 막대한 사회기반시설 확충 및 주택건설이 추진됨으로써 국가경제에서 차지하는 비중이 지속적으로 증가되어 왔다. 1) 이러한 건설산업에서 콘크리트는 성형성 및 경제성이 우수한 구조재료이기 때문에 현재까지 그 수요가 증가하고 있는 실정이며, 콘크리트를 대체할 수 있는 구조재료가 개발되지 않는 이상 지속적인 수요급증이 예측된다.

A Study on the Evaluation of Field Application of High-Fluidity Concrete Containing High Volume Fly Ash

In the recent concrete industry, high-fluidity concrete is being widely used for the pouring of dense reinforced concrete. Normally, in the case of high-fluidity concrete, it includes high binder contents, so it is necessary to replace part of the cement through admixtures such as fly ash to procure economic feasibility and durability. This study shows the mechanical properties and field applicability of high-fluidity concrete using mass of fly ash as alternative materials of cement. The high-fluidity concrete mixed with 50% fly ash was measured to manufacture concrete that applies low water/binder ratio to measure the mechanical characteristics as compressive strength and elastic modulus. Also, in order to evaluate the field applicability, high-fluidity concrete containing high volume fly ash was evaluated for fluidity, compressive strength, heat of hydration, and drying shrinkage of concrete.

A Study on the Quality Properties of Exposed High Fluidity Concrete using Fly Ash and Limestone Powder

Recently, the interest is increasing about the exposed concrete, accordingly, exposed concrete is expanding the use. However, concrete structures is difficult to apply the general concrete for exposed concrete, due to complex section and compact reinforcement, increasingly. Therefore, in this paper, for application of high fluidity concrete as exposed concrete, exposed high fluidity concrete using fly ash and lime stone powder was manufactured and observed quality property(fluidity properties, mechanical properties and Surface Properties) of exposed high fluidity concrete. The experiments are based on the OPC and LSP10, was evaluated Impact on the quality of concrete according to mixing ratio of FA(0, 10, 15 and 20). As a result, fluidity properties, mechanical properties and Surface Properties of exposed high fluidity concrete were satisfied to requirement conditions, fluidity and surface finishability was improved depending on mix of fly ash and limestone powder. Through this, we utilize of basic research data for development of high fluidity concrete for exposed concrete.

Mechanical Properties of the High Flowing Self-Compacting Concrete for Members of Bridge Overcrowded Arrangement of Bar

Domestically, application of High Flowing Self-Compacting Concrete (HSCC) is limited to building structures and it is difficult to find examples of application in civil infrastructural constructions. However, in the case of North America and Europe, by introducing precast and prestressed system, HSCC is being used for high-density reinforced bridge members. Hence it is assessed that broadening the utilization of HSCC into areas such as bridges and civil construction is required. Therefore in this research, to apply HSCC to high-density reinforced bridge members, ground granulated blast-furnace slag and fly ash were mixed in binary and ternary systems. Also the dynamical characteristics of HSCC, following 1st class regulations of Japan Society of Civil Engineers (JSCE), were assessed to enable application on high-density reinforced structures. The test results revealed ternary system mixture showed better mechanical characteristics than binary system mixture and the application on high-density reinforced precast bridge members seems possible.

The Quality Properties of Self-Compacting Concrete Mixed with Tailing from the Sangdong Tungsten Mine

This study has focused on the possibility for recycling of tailings from the Sangdong tungsten mine as powder(TA) of self-compacting concrete(SCC). The experimental tests for slump-flow, time required to reach 500 mm of slump flow(sec), time required to flow through V-funnel(sec) and filling height of U-box test(mm) were carried out in accordance with the specified by the Japanese Society of Civil Engineering(JSCE). The results of this study, slump-flow of SCC was satisfied a prescribed range. And time required to reach 500 mm of slump flow(sec) and time required to flow through V-funnel(sec) decreased with increasing replacement of TA. But filling height of U-box test(mm), replacement of TA up to 30% were satisfied a prescribed range. The mechanical properties including compressive strength, splitting tensile strength and elastic modulus were checked with the requirements specified by Korean Industrial Standards(KS). The compressive strength of SCC decreased with increasing replacement of TA, splitting tensile strength and elastic modulus were similar to those of normal concrete. The fundamental durability was reviewed through the dry shrinkage rate and accelerated carbonation tests. As the result dry shrinkage rate and accelerated carbonation depth increased with increasing replacement of TA.