순환골재 내부의 미세균열 발생형태 및 흡수 특성

최희복,김백중,강경인,이종구,Choi, Hee-Bok,Kim, Beak-Joong,Kang, Kyung-In,Yi, Chong-Ku 대한건축학회 2011 대한건축학회논문집 Vol.27 No.3

Many researchers have reported strength reduction of concrete when recycled aggregate is introduced to the mix. However, the causes of such reduction and preventive measures are yet to be established. In this study, effect of recycled aggregate on concrete is investigated by microscopic examinations of micro-cracks present in the recycled aggregate (RG) and by measuring moisture absorption rate of RG. The results showed the followings: 1) the shape and extent of micro-cracks vary by type and size of RG, 2) recycled aggregate concrete (RAC) containing RG formed the failure surface along the micro-cracks inside RG, 3) moisture uptake, which may alter local water content in wet concrete, mostly took place via micro-cracks of RG reaching depth of about 3 mm within the first 1 hr, much faster rate than that of natural aggregate of the same type. Based on the results of this study, it is recommended that the size of RG be kept less than 10 mm for production of high quality RG with a small amount of micro-cracks.

TEMPCORE 철근의 마디ㆍ리브 나사식 기계적 이음법 개발에 관한 연구

최희복(Choi Hee-Bok),김광희(Kim Gwang-Hee),김재엽(Kim Jae-Yup),서덕석(Seo Deok-Seok),강경인(Kang Kyung-In) 대한건축학회 2003 大韓建築學會論文集 : 構造系 Vol.19 No.3

Recently, Re-bar production method is being changed to method of tempcore re-bar that consist of two parts. a part, the core of tempcore re-bar, that has ferrite structure of excellent ductility and the other part, the surface of Tempcore re-bar, that has martensite structure of high relative stiffness. Therefore, the purpose of this research is to develop a re-bar mechanical connection that minimizes the decrease in relative stiffness of re-bar surface and to compensate flaw of previous screw type re-bar mechanical connection by performing screw processing only on the rib and node of re-bar This research was performed static tensile test for HD25, HD29 and HD32 re-bars and was also performed cyclic tensile test for D25, D29, HD25 and HD32 re-bars. And it was compared performance of maximum tensile strength and strain intensity to ACI Code ( maximum tensile strength shall be more than 125% of yield strength, strain intensity(δs)≤0.3) and then reviewed the future possibility for application. The results of this research are as follows; 1) static tensile test is revealed to be more than 140% of yield strength 2) and maximum cyclic tensile test is revealed to be more than 160% of yield strength. 3) displacement is apposite to limitation of allowable displacement(δs≤0.3). The results of tests of all specimens are complying with ACI Code of re-bar mechanical connection.

절곡 후 펴기작업에 의한 철근의 성능변화 및 대책에 관한 연구

최희복(Choi Hee-Bok),김현석(Kim Hyun-Seok),서덕석(Seo Deok-Seok),강경인(Kang Kyung-In) 대한건축학회 2003 大韓建築學會論文集 : 構造系 Vol.19 No.9

As mass of buildings are getting bigger, more complicated and skyrocked building structure frames are changed. As a result, when each member is connected that necessarily reinforcing bar is occurred by bending and straightening in top-down method, tilt-up method, open in a slab and a stair hall and so on.<br/> In this experiment, we distribute the bending angle to 60, 90 and 120. We separate them into two groups. One is straightening right after bending and the other is straightening after one week. We will use the bars whose size is HD13 and HD16. The number of tests will be 60 times. <br/> In the case of HD16, the increase of bending angle is decreased in yield strength and maximum strength of bar. And compared with thinner bars, HD16 is showed bigger differences in yield strength and maximum strength of bar when the 'being bent' duration get longer. <br/> Top-down method and tilt-up method more often need an additional measure, especially at the point of time linking the materials together, to bend reinforcing bars of slab open and stair case, and then strengthen them afterwards, which requires more than 20-30% yield strength and maximum strength respectively.<br/> In short, In planning and structuring a building, above-mentioned supplementary reinforcement should be taken into consideration.

순환골재 내부의 미세균열 발생형태 및 흡수 특성

최희복(Choi Hee-Bok),김백중(Kim Beak-Joong),강경인(Kang Kyung-In),이종구(Yi Chong-Ku) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.3

Many researchers have reported strength reduction of concrete when recycled aggregate is introduced to the mix. However, the causes of such reduction and preventive measures are yet to be established. In this study, effect of recycled aggregate on concrete is investigated by microscopic examinations of micro-cracks present in the recycled aggregate (RG) and by measuring moisture absorption rate of RG. The results showed the followings: 1) the shape and extent of micro-cracks vary by type and size of RG, 2) recycled aggregate concrete (RAC) containing RG formed the failure surface along the micro-cracks inside RG, 3) moisture uptake, which may alter local water content in wet concrete, mostly took place via micro-cracks of RG reaching depth of about 3 ㎜ within the first 1 hr, much faster rate than that of natural aggregate of the same type. Based on the results of this study, it is recommended that the size of RG be kept less than 10 ㎜ for production of high quality RG with a small amount of micro-cracks.

재생골재를 사용한 콘크리트 배합시 적정 잔골재율에 관한 연구

최희복(Choi Hee-Bok),안성훈(An Sung-Hoon),박희곤(Park Hee-Gon),윤지언(Yoon Jie-Eon),김춘학(Kim Chun-Hak),강경인(Kang Kyung-In) 대한건축학회 2005 大韓建築學會論文集 : 構造系 Vol.21 No.11

살리실산 에탄올 용해법을 이용한 고로슬래그미분말의 정량화를 위한 실험적 연구

최희복(Choi Hee-Bok),강경인(Kang Kyung-In) 대한건축학회 2009 大韓建築學會論文集 : 構造系 Vol.25 No.9

In Japan, the standard for blast furnace slag cement and concrete get readied and, they are utilizing much blast furnace slag for a special concrete used in sea construction etc.. But, in domestic, it is existing state that a standard about this gets not readied yet. Thereby, the blast furnace slag cement and concrete is used to normal concrete as unlawful by the ready-mixed concrete companies. Therefore, this research will bring into the open the use of blast furnace slag cement and concrete. We propose the salicylic acid ethanol melting method as one that can quantify the included blast furnace slag to cement and concrete. Result of a laboratory that applied salicylic acid ethanol melting method, it could receive exactitude as error rate of the 5% more or less. Also, we collected two kinds of fresh blast furnace slag concrete from ready-mixed concrete that is carried in building site, and result that carried out an experiment equally by the method that did in a laboratory experiment with the samples was obtainable high accuracy as error rate of about 5%, too. Experiment result until now, it is considered that the salicylic acid ethanol melting method that is quantitative method of blast furnace slag cement and concrete proposed in this research is practicality very. Although, in this research, it studied to fresh concrete, it is forward research task that grope method to measure quantity of blast furnace slag powder in hardened concrete interior.

고로시멘트콘크리트의 현장 적용성 평가

최희복(Choi Hee-Bok),강경인(Kang Kyung-In) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.7

To estimate possibility and problem of blast furnace slag cement and concrete, in the filed application of the blast furnace slag cement and concrete, the blast furnace slag concrete that is alternated by S/P 40% applied to bottom slab of a parking place of apartment underground and mass member of a laboratory and it measured compressive strength, length change and heat of hydration by a curing method. 1) In case of S/C, the early development rate of compressive strength appeared relatively lower than it of OPC, but, since age 14 day, the development rate of compressive strength of the S/C appeared almost analogously with it of the OPC. 2) The drying shrinkage of S/C is happened 70% of whole drying shrinkage in early 12 hours. 3) Until about 80 hours within after placing, heat of hydration of OPC was higher about 10℃(17%) than that of S/C. And for maximum peak hour of heat of hydration, OPC appeared at about age 25 hours before and after. However S/C appeared at 68 hours before and after. 4) Drying shrinkage change in the horizontal axis of cast in place concrete, the same as mass member, the S/C showed bigger length change than it of the OPC. And length change happened within 8~10 hours after placing, and after that time, a length change was no longer happened. Drying shrinkage about the axis of ordinates of concrete is smaller than dry shrinkage of the horizontal axis. And drying shrinkage about the axis of ordinates too is happened bigger in S/C similarly with the horizontal axis. 5) After cast-in place concrete placing, the heat of hydration did not increase since the after this while rise steadily for about 16 hours since early age.

순환골재콘크리트와 이형철근 사이의 부착성능

최희복(Choi Hee-Bok),강경인(Kang Kyung-In) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.3

This research is main object to study bond performance between concrete and rebar by the replacing ratio of recycled aggregate and the quality of recycled aggregate etc. as main experiment factor. Result is as following. 1) Slip was small or similar than normal concrete to replacing ratio 50% of recycled aggregate, increased in concrete that replacing ratio 100% of recycled aggregate. 2) Bond strength of recycled coarse aggregate concrete was similar with normal concrete, but bond strength of recycled fine aggregate concrete decreased according as recycled aggregate replacing ratio increases. 3) The τb/√fck of recycled aggregate concrete decreased according as relative absorption increases, and decrease tilt of τb/√fck is obvious in more than relative absorption 3. 4) According as water-cement ratio is decrescent, the τb/√fck of recycled aggregate concrete decreased, and specially it was notable in recycled fine aggregate concrete.

재생골재 적용 콘크리트의 강도예측 - 신경망 기법과 적산온도방식 강도예측 -

최희복(Choi Hee-Bok),김광희(Kim Gwang-Hee),강경인(Kang Kyung-In) 대한건축학회 2005 大韓建築學會論文集 : 構造系 Vol.21 No.6

국내 건설 폐기물 활용 현황 및 활성화에 관한 연구

장재명,최희복,강경인,Jang, Jae-Moung,Choi, Hee-Bok,Kang, Kyung-In 한국건축시공학회 2003 한국건축시공학회지 Vol.3 No.1

Recently, the amount of the construction and demolition wastes has rapidly increased due to increasing construction projects. In the past, most of the construction and demolition wastes were buried in the ground of thrown away. Illegally, without any treatment, so various harmful environmental pollution problems were occurred. In this study, the domestic data on the amount of the construction and demolition wastes and the disposal methods were collection and analysed. Specially, the recycling and management systems of the construction and asphalt concrete wastes were studied. A new technology and necessary policy for recycling were suggested. In general, the industrial wastes were produced in the particular place, and the amount and the characteristics of the wastes able to be estimated by the studies on the treatment technology. And the investment of the facilities for the industrial wastes have been made continuously. But little attention has been relatively given to the treatment technology. And system for the construction and demolition wastes for the political support and facilitation on the proper treatment and the recycling, the necessary of information exchange system and the manifest system for treatment of waste on commission were recommended, and also devised methods to develope and support the recycling industry. In the future, the subject of study is going to carry out analysis of economic and market in making products.