혼화재 종류별 온도 변화에 따른 콘크리트의 응결 및 강도발현 특성

주은희,손명수,차천수,한민철,김성수,한천구 대한건축학회 2004 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.24 No.1(구조계)

The objective the paper is to investigate the physical and mechanical properties of concrete incorporating mineral admixtures. For setting properties, at low curing temperature, setting time of concrete with mineral admixture is delayed compared with that of plain concrete. But, use of cement kiln dust(CKD) has a desirable effect on reducing setting retard under low curing temperature. For compressive strength, concrete with FA and BS have low strength at early stage compared with that of plain concrete under low curing temperature. However, the use of CKD resulted in an enhancement of compressive strength at early stage under low curing temperature, and exhibited a similar level of compressive strength with plain concrete. For this reason, use of CKD in cold weather concreting has positive effect on strength development at low curing temperature under early age.

방화석고보드 두께 및 접착방식 변화에 따른 고강도 콘크리트의 폭렬특성

한천구,배장춘,장기현 청주대학교 산업과학연구소 2008 産業科學硏究 Vol.26 No.1

This study investigates fire resistance properties of high strength concrete designed with various thickness and adhesive methods of fireproof gypsum board. Test results showed that compressive strength of control concrete indicated 89.9MPa, which is high strength rage. For the fire test results, uncovering top section of specimens caused severe spalling occurrence in all sides, exposing mostly re-bars. Moreover, some specimens even exposed main bars of concrete. However, covering top section of specimens protected from fire and resulted in secured high strength concrete. The maximum temperature of main bars in 19BN-W indicated 1017℃, in 19MB-W was 1061℃, in 19MN-W was 1036℃, in 25MB-W was 583℃ and in 19MN-T was 271℃ respectively. 19MB-W had the highest value of weight loss ratio, indicating 54%, while 25MB-W showed 43% of weight loss ratio, 19BN-W was around 40%, 19MN-W was around 27% and 19MN-T was around 7%.

3종류 잔골재를 조합 사용한 시멘트 모르터의 특성

한천구,윤기원,박용규 청주대학교 산업과학연구소 2005 産業科學硏究 Vol.23 No.1

This paper investigated the engineering properties of cement mortar mixed with more than two kinds of fine aggregate. For fresh mortar properties, unit volume weight is constant regardless of mixing content and type of fine aggregate. An increase in contents of natural fine aggregate and crushed fine aggregate resulted in an increase in flow, whereas an increase in recycled fine aggregate contents reduced flow. Gap between maximum flow in N_(3)C_(0)R_(0) and minimum flow in N_(0)C_(0)R_(3) exhibited about 12%. Compressive strength at 28 days ranged from 32 to 36 MPa in order for crushed fine aggregate, natural fine aggregate and crushed fine aggregate showed compressive strength comparable to that of crushed fine aggregate. An increase of fraction of recycled fine aggregate in mixed fine aggregate resulted in a decrease in compressive strength. For drying shrinkage, N_(0)C_(0)R_(3) had the largest drying shrinkage among various mixture type. The combination of large contents of recycled fine aggregate and small contents of natural and crushed fine aggregate had a large amount of drying shrinkage.

주택성능등급제에 따른 레미콘 산업의 대응방안

한천구,이건철,오상백,박용규 청주대학교 산업과학연구소 2006 産業科學硏究 Vol.24 No.1

This study investigates the regulations on concrete grade evaluation, in response to operation of housing performance grade system(HGS). It also studies countermeasure- of ready mixed concrete industry. Because the HGS provide people who have to invest in housing once during their whole life, with objective information of housing performance, housing consumers would easily understand and purchase better house. In addition housing construction companies will try to supply the high quality housing, in response to people's various housing performance needs. It is expected that housing quality improvement and housing components technology development will be nationally activated, due to the competition on housing quality between the construction companies. After this, HGS is now on design process but will be on construction process connecting specification, which is perfoiniance based design and on the process after completion. It is assumed that those regulations will be possibly continued to develope for housing performance guarantee system.

슈미트햄머의 반발도 및 초음파속도에 미치는 결합재의 영향

한민철,이백수,윤기원,최영화,한천구 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.1(구조계)

This paper reports the influence of kinds of cement and replacing ratio of fly ash(FA) and blast furnace slag powder(BS) on estimation of compressive strength by non-destructive test. According to the results, the compressive strength, the rebound value of schmidt hammer and ultrasonic pulse velocity show the higher value in order of AMC, UHC and OPC. In concrete replaced with mineral admixture, they are lower at early age, but higher at the age of 91 days compared with plain concrete. As the influence of the kinds of cement, estimated compressive strength by Schmidt hammer is almost same in the case of UHC, but much lower at the same rebound value in the case of AMC, in comparison with OPC. But the influence of mineral admixture is very insignificant. Compressive strength estimated by ultrasonic pulse velocity method shows the higher value by 10MPa, 12.5MPa in the case of UHC and AMC respectively compared with OPC, and the influence of mineral admixture on ultrasonic pulse velocity is insignificant.

고속가공용 엔드밀 형상설계 S/W 개발

한창규,고성림,서천석,김경배 한국공작기계학회 2004 한국공작기계학회 추계학술대회논문집 Vol.2004 No.-

The tool geometry parameters and cutting process have complex relationships. Until now, various cutting test were needed to acquire optimal design of end mill for the purpose of high speed machining, due to the insufficient knowledge about cutting process in high speed machining. Using various tools with different geometry, relationships between tool geometry parameter (rake angle, clearance angle, length of cutter) and cutting process (cutting force, surface accuracy, surface roughness) have been studied. Acquired data can be used to design optimal tool for high speed machining and to develop a software for design of end mill geometry.

유기질 섬유 보강재를 사용한 시멘트 모르터의 특성

한천구,이건철,신현섭 청주대학교 산업과학연구소 2006 産業科學硏究 Vol.23 No.2

This study reported the result of experiments as to engineering properties of cement mortar with organic fiber types, such as cellulose(CEL), nylon(NY), polypropylene(PP) and polyvinyl Alcohol (PVA) and their contents. For the properties of fresh concrete, slump flow of almost all concrete, adding fiber less than 0.1% by volume, increased, but the flow of concrete adding more than 0.1% decreased, except for PVA fiber. Furthermore, air content increased as NY and PP fiber content increase, and PVA fiber content decrease. For the properties of hardened concrete, compressive strength at early age had no significant effect, but the strength value of concrete adding 0.1%, at 28 days, increased. This test results demonstrated that proper amounts of fiber have favorable strength value. Tensile strength of concrete adding 0.1%~0.15% also exhibited improved value, especially adding NY fiber, was pretty remarkable, even if physical properties and improved air content are considered. For the dry shrinkage properties, increase of CEL and PP fiber content resulted in first increase and decrease. However, increase of dry shrinkage was proportional to the increase of NY and PVA fiber content.

혼화재 다량 치환 콘크리트의 품질향상에 관한 기초적 연구

한천구 청주대학교 2009 産業科學硏究 Vol.26 No.2

In this study, it was designed to devise a quality improvement method to make up for the problems that are occurring when the mineral admixtures like FA(Fly-Ash) and BS(Blast Furnace Slag) are used in great quantity, by approaching the methods from chemical and physical basis. And the summarized contents are as follows. As for the concrete properties before setting, in the case of fluidity, the EAE(Early AE agent) appeared to have highest value but the FCE(Fine Particle Cement) appeared to have the lowest value among the admixtures. And other mixtures did not appeared to be much different from OPC, and in the case of air, it was identified that besides the B-P mixture, all other mixtures could not reach the target air content. As for the setting time, the mixture of NAO(NaOH) and FCE brought about the relatively satisfactory results, which are the alkali activators as the quality improvement admixtures. As for the properties of hardened concrete, the semi-adiabatic temperature history appeared to be high when it was NAO at the BS and in the case of quality improvement admixtures, but in the other cases it appeared to be similar to the plain mixtures or a little lower than the plain mixture. In the case of compressive strength, all kinds of quality improvement admixtures appeared to be lower than the plain mixture, but in the case of BS, the NAO was satisfactory at the third day of the early stage of age. And in the case of mixture where the large quantity of FA and BS were used, the FCE appeared to be most excellent at the 91st day of aging.

수축저감제 혼입률 변화에 따른 콘크리트의 공학적 특성에 관한 연구

한민철,金光華,정규문,정평유,윤성노,한천구 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.2

In this paper, tests are carried out using concrete incorporating shrinkage reducing agent(SR) in order to investigate the engineering properties of concrete. The contents of SR and W/C are varied. According to test results, as for fresh concrete, as SR content increases, slump and air content shows decline tendency, and setting time is accelerated with increase of SR content and decrease of W/C. As for compressive strength, as SR contents increases compressive strength shows to be decreased. As for the effect of SR on drying shrinkage, it shows to be reduced with increase of SR content. This is due to the reduced surface tensile strength of water and tensile strength of capillary pore in concrete.

석회암 성분의 부순잔골재를 사용한 모르터의 역학적 특성

한천구 청주대학교 산업과학연구소 2006 産業科學硏究 Vol.24 No.1

This study investigates engineering properties of mortar using limestone-crushed-aggregate (LS). Test resulted show, that increase of incorporating ratio of Ls had better fluidity than other specimens. This is due to the particle shape and continuous grade distribution of Ls. In addition, mortar incorporating more Ls exhibited lower air content, by the well-filling effects of the aggregate. Among specimens, It was found that Ls affected to the setting time of the mortar, resulting from acceleration of the initial and final setting time. For the properties of strength, specimens incorporating higher ratio of Ls had favorable strength, such as higher compressive, tensile and flexural values, Drying shrinkage length, change ratio of the specimens exhibited that Ls was the lowest and it reduced the shrinkage, as the incorporating ratio of Ls increased, due to the improved strength.