초고층 건축물용 80 MPa급 고성능 콘크리트의 펌프압송에 따른 공학적 특성

정은봉 청주대학교 일반대학원 2014 국내석사

Recently, high rise buildings have been constructed with the trends of pursuing high rise and enlargement, so pump car placement is being generally applied in terms of workability and economic feasibility as the most excellent placement method. However, the high strength concrete used to construct super high-rise buildings are expected to raise various problems at the pumping of high pressure; therefore, a lot of researchers have conducted a series of tests related to the pumping in diverse ways and reported the findings so far. However, the results are so different from one another, and most of them deal with the tests on horizontal pumping performances only. Accordingly, this study aims to consider the actual pumping performances of the vertical pipe. To attain the goal, the researcher selected super high-rise building projects in which the vertical height of the pumping was higher than 500 m. According to the vertical height of the pumping of 80 MPa high performance concrete placed, the study intends to analyze the quality fluctuations of the concrete before and after the pumping and also evaluate its rheological properties. (1) According to the result of analyzing the fluid properties of the concrete unhardened before and after the pumping by the height of it, its slump flow, slump, and air quantity and temperature tended to increase more compared with those before the pumping. However, T-500 showed reduction after the pumping. Also, the content of chlorides measured indicated subtle difference before and after the pumping. And according to the result of evaluating the segregation of the concrete quantitatively based on the Evaluation Index for Segregation (EIS), the EIS value ranged from 2.2 to 2.4, so in terms of its performance, it indicated the excellent index reaching either the 1st or 2nd grade. (2) Regarding the result of evaluating the filling through the V-lot time of flow and the U-Box filling test before and after the pumping by the height of it, the result of the V-lot time of flow test showed that the decrement of viscosity led to the reduction of time of about 45 %. And the result of the U-Box filling test showed that there was no significant difference before and after the pumping and both satisfied the range of the site management itself. (3) The concrete’s yield stress and plastic viscosity were quantitatively evaluated by using the related equipment. And both its yield stress and plastic viscosity were significantly reduced up to 50% or so after the pumping due to the reduction of the concrete’s viscosity. Also, its yield stress and plastic viscosity were compared with quantitative evaluation as well as philological evaluation, and both showed that they had low correlation of about 10 to 30 %. (4) According to the result of measuring the concrete’s compressive strength and elastic coefficient by age before and after the pumping based on the height of it, one of the dynamic properties, the 7th day showed about 14 %, the 28th day about 8 %, and the 56th day about 10 %; therefore, as the age gets higher, it tends to increase comparatively more after the pumping in general. And the elastic coefficient, too, tends to increase as the compressive strength increases.

13 mm이하 순환 굵은골재 치환사용에 의한 연속입도 콘크리트의 공학적 특성

강병회 청주대학교 대학원 2015 국내석사

In this research, as a solution of environmental load and exhaust of natural resources due to the increased construction wastes, the recycled aggregate extracted from building waste is sieved for 13 mm size aggregate and replaced to 13 to 25 mm manufactured coarse aggregate to obtain well-graded aggregate conditions. Using this aggregate, the method for securing favorable properties of concrete is suggested. The result of a series of the experiment is as follow. (1) The plain concrete without replacement of 5-13 mm recycled coarse aggregate used the aggregate with less fines although it could be passed KS standard gradation. Hence, it was known that replacing 5 to 13 mm of recycled aggregate is necessary to supply fines and achieve good gradation. (2) For the workability of the concrete, when the concrete contained the aggregate replaced 5 to 13 mm of recycled coarse aggregate, the workability was improved. Especially, about 30 % of 5 to 13 mm recycled coarse aggregate replacement showed better workability than the concrete without replacement of 5 to 13 mm recycled coarse aggregate. Although the gradation of aggregate used was well-graded, over the threshold of 30 % of replacement, decreased workability was observed. (3) For the air content of the concrete mixtures, regardless of water-to-cement ratio, as the replacement ratio of 5 to 13 mm recycled coarse aggregate is increased, the air content of the concrete mixture was decreased. It is considered that the decreased the volume of voids due to the well-graded aggregate with replacement. On the other hand, over 50 % of replacement of 5 to 13 mm recycled coarse aggregate caused increased air content of the concrete mixture because of increased air voids. In the case of unit weight, regardless of water-to-cement ratio, the values were changed related with the amount of air in the concrete mixtures. In the case of 100 % replacement of 5 to 13 mm of recycled coarse aggregate, however, decreased unit weight was obtained because of lighter density of recycled aggregate than the density of manufactured aggregate. (4) The compressive strength of the concrete mixture replaced 5 to 13 mm recycled coarse aggregate was increased due to the well-graded aggregate and thus densely filled microstructure. Especually, when the 5 to 13 mm of recycled coarse aggregate was replaced 30 %, the highest compressive strength was achieved and this value was similar to the concrete replaced with 5 to 13 mm of manufactured coarse aggregate. In the case of drying shrinkage, although there was no significant difference, recycled aggregate replacement contributed decreasing drying shrinkage. In summary, replacing the recycled coarse aggregate of 5 to 13 mm of size for 30 %, a good grade of aggregate was achieved and thus general quality improvement and financial advantages were obtained. Additionally, as increasing the utilization of recycled aggregate, it is expected to contribute on providing the solution of reducing environmental load and the method of preferred quality of concrete with low cost.

등가재령 방법에 의한 혼화재 치환 고강도 모르타르의 자기수축 평가

김태선 청주대학교 대학원 2015 국내석사

The objective of this research is to investigate an effect of curing temperature on autogenous shrinkage of high strength mortar with 0.15 water-to-binder ratio incorporating fly ash (FA), blast furnace slag (BS), and silica fume (SF) in terms of equivalent age. The replacement ratios of FA, BS, and SF were varied from 10 % to 30 %. The curing temperatures were prepared with 5°C, 20°C and 35°C as the parameters based on the assumption of the climate condition in the practical field. Non-linear regression model applying equivalent age was used to estimate the autogenous shrinkage. (1) The autogenous shrinkage of the concrete showed rapid shrinkage within the first three days while slow trend of shrinkage was shown after third day. (2) Depending on the curing temperature, as the curing temperature was increased, the amount of shrinkage was increased. Namely, although there was no significant change at early ages, as the curing age was increased, relatively more shrinkage was observed in 35°C while less shrinkage was observed at 5°C for same ages. (3) Although there are significant differences in 5°C of curing temperature conditions, similar shrinkage was observed in both 20 and 35°C, and thus it was considered that evaluation of maturity is hard to apply in these conditions. (4) When using the Ea value at hardening phase for analysis of autogenous shrinkage depending on equivalent age, it is considered that more accurate evaluated results can be obtained. The accurate selection of Ea value will contribute on the evaluation of temperature dependency on autogenous shrinkage. (5) As an analysis of correlation between setting and hardening phases using Tazawa model and power model, better correlationship was achieved for hardening phase than setting phase and power model showed better correlationship than Tazawa model. In this research scope, as a result obtained from the hydration under the constant curing conditions, the influence of curing temperature on autogenous shrinkage was evaluated using equivalent age method, and it is considered that accurate Ea value selection is required based on the conditions of mix design and mixed materials for entire life term for accurate analysis.

유기섬유 및 폴리머의 조합사용이 콘크리트의 균열저감에 미치는 영향

박재용 청주대학교 대학원 2015 국내석사

Concrete has an outstanding compressive strength while very low tensile strength and brittle behaviors. Because of brittle behaviors of the concrete, the concrete structure suffers cracking in the tensile area, and thus durability and safety of the structure are the problems. As an alternative of these problems, fiber-reinforced concrete has been suggested and the most representative fiber types used in fiber-reinforced concrete are polypropylene (PP), polyethylene (PE), steel, and Nylon (NY), etc., and many research has been performed. However, there are many problems of applications on the practical cases due to not enough comparing data base and loss of strength due to poor dispersion of the fiber and poor adhesiveness of the fiber in cement paste system. Therefore, in this research, expecting the improvement of fiber-reinforced concrete including combination of polymer and organic fibers, the optimum combinations of organic fibers and polymer is suggested based on the influence of the types and amount of the fibers. Furthermore, the performance of the organic fibers are compared with the Cellulose fiber. The result of a series of the experiments are as follow; (1) As a fundamental properties of concrete including polymer and organic fibers, because of the ball-bearing effect of polymer and entrained air, and dispersion effect of the surfactant caused by the polymer admixture, the workability of the concrete was increased. On the other hand, Cell fiber is considered as a reason of decreased workability due to the absorbing mixing water. (2) The air content was increased as the amount of fiber was increased. This is likely caused by increased the amount of the entrapped air by the added fibers. The setting times were measured in the exposed conditions. The average time of initial set and final set of plain mixture was 3 hours 45 minutes, and 4 hours 50 minutes, respectively. In the case of PM-NY, the fastest case was the initial and final set was 1 hour 50 minutes, and 2 hours 10 minutes, respectively. (3) For the compressive strength properties, no clear trend was observed while all cases satisfied target compressive strength for 21 MPa grade. For 24 MPa grade, there was increased trend with adding polymers in the concrete mixture. It is considered as the result of continuous hydration of cement paste due to the preventing evaporation of moisture by membrane produced by polymer. If the air content is controlled, improved compressive strength can be expected. (4) For tensile strength properties, similar to the result of compressive strength, 21 MPa grade did not show specific trend. However, for the 24 MPa grade, tensile strength was increased with increased fiber amount. This is considered as the results of ball-bearing effect by polymer and dispersion by surfactant. For the second phase experiment, the tensile strength was obtained only 10 % of compressive strength and very slight increase of tensile strength was observed with increased amount of the fiber. (5) All crack lengths of fiber reinforced specimens were shorter than the crack lengths of plain specimen. This is likely the crack preventing effect of the fibers reinforced. The width of cracks wcere measured for the cracks larger than 0.1 mm. The concrete specimen including cell fiber showed increased cracking because of the decreased workability by absorbed moisture. (6) The result of measuring width of crack was also showed decreased width of crack by the fiber reinforcement. From the cracking space calculated by the length times the width, fiber reinforced specimens showed maximum and minimum of 60 % and 30 % to the plain specimen of improvement were shown. In summary, the workability of concrete was increased with increased fiber because of increased the amount of the polymer, while significantly decreased slump was observed when the fiber was added excessively. The air content was increased with increased amount of fibers due to the increased entrapped air. For the Cell fiber, workability of the concrete was decreased because of the absorption of moisture, while the dispersion of fiber was improved because of the entrained air and surface activity. Because of this effect, the compressive strength, tensile strength, and crack resistance performance were improved. Based on the workability, strengths, crack resistance, and economic feasibility, NY fiber can be suggested as an optimum fiber for the concrete mixture.

굵은골재 암종변화가 초고강도 콘크리트의 공학적 특성에 미치는 영향

정상운 청주대학교 대학원 2015 국내석사

As the society has been developed rapidly, the building structures have become high rising and large scale, and thus the materials, structure, design, and construction techniques were required for these expanded building structures. In the case of construction materials, specifically concrete, has been developed to high strength of four times higher compressive strength, high durability of about 200 year life, and high fluidity of flowing like water. On the other hand, the aggregates which consist approximately 70 to 80 % of entire concrete volume have been suffered breakage rather than failure at ITZ where in between aggregate and cement paste because of the increased strength at ITZ for the high strength concrete. Therefore, in this research, to select appropriate aggregate type for 80 MPa grade high strength concrete, a series of experiments were conducted about fundamental properties and engineering properties of the concrete with various aggregate types. The results from the experiments can be summarized as follow. 1) Granular aggregate (GA), Recycled limestone aggregate (RLA), Recycled high silica limestone aggregate (HSRLA), and Basalt aggregate (BA) were selected as the sample aggregates based on the survey about the aggregates used for high strength concrete in Korea and abroad. From the aggregate quality tests, the properties of each aggregate were satisfied KS standards. 2) From the fresh state concrete properties in Series I, slump flow was satisfied with all types of aggregate and in the case of RLA and BA showed better workability than GA. Regardless of water-to-binder ratio, air contents of entire concrete mixtures were satisfied target air content. There was no significant effect of aggregate types on setting time. For the hardened concrete properties, all mixtures showed over 80 MPa of compressive strength at 28 days age regardless water-to-binder ratio and types of aggregate. The concrete mixtures including ga and BA showed relatively lower elastic modulus than the concrete mixture including RLA and HSRLA, so that RLA and HSRLA are considered as a good aggregate for application in high strength range. For the autogenous shrinkage, when the w/c of concrete mixture is increased, the autogenous shrinkage was increased, and RLA showed favorable performance of preventing autogenous shrinkage. 3) Fresh state properties of concrete in Series II, in the case of w/c is 0.20, the concrete mixture including GA showed satisfied target slump flow with 2.0 % of superpalsticizer and the concrete mixtures including RLA and HSRLA satisfied target slump flow with 10 % less superplasticizer. When w/b is 25 %, GA decreased the amount of SP for 1.8 %, and RLA and HSRLA decreased 1.6 % for satisfying target workability. Therefore, approximately 11 % of superplasticizer could be saved. As hardened concrete properties, at 7 days of age, there was no significant difference for different w/b. In 28 days of age, the compressive strength of the concrete mixture of 0.20 w/b showed increased compressive strength than 0.25 w/b concrete mixture. Also in 28 days of age, all specimens satisfied over 80 MPa of compressive strength regardless w/b and types of aggregate. Based on the manufacturing cost of different types of aggregate and each aggegate’s workability, strength, elastic modulus, and autogenous shrinkage, RLA was determined as the most favorable aggregate by the economical feasibility. Therefore, as a result of economical feasibility of RLA, it showed the possibility of saving about 4,700 KRW rather than GA in concrete mixture. As a summary, based on the comparing workability, compressive strength, elastic modulus, autogenous shrinkage, and cost, RLA was the most appropriate aggregate for manufacturing 80 MPa grade high-strength concrete with favorable workability, strength, and economical advantage.

기후요소에 의한 건축공사 작업불능일 산정에 관한 연구

박인범 청주대학교 대학원 2010 국내석사

본 연구에서는 기후요소에 의한 건설공사 작업불능일의 효율적 산정을 위하여 기상청 자료를 토대로 과거 1, 5, 10 및 30년간의 전국 1개 특별시와 6개 광역시 및 청주지역을 대상으로 통계년수에 따른 기후요소에 의한 작업불능일을 산정하고 이들의 변동을 분석하여 기후변동이 합리적으로 반영된 작업불능일 산정을 위한 통계년수를 제시하고자 하였는데, 그 결과를 요약하면 다음과 같다. (1) 각 기관별 작업불능일 산정 기준을 조사한 결과 대한주택공사 표준시방서에는 우리나라 전국 지역을 평균 기온에 따라 1~6급지로 구분하여 동절기 공사 중단 기간을 최소 15일부터 최대 115일까지의 기간을 산정하고 있었고, 미 공병단 계약서(COE)에서는 우리나라 지역을 16개로 나누어 각 지역별 작업불능일수를 규정하고 있었다. 또한, 선행연구 및 기타 각 기관의 규정을 살펴보면, 기후요소에 의한 작업불능일 산정 기준 및 통계년수가 매우 다르기 때문에 실무 건설공사현장에서 작업불능일 산정을 위한 통일된 지침이 부재하고 이로인해 효율적인 작업불능일 산정이 어려움을 알 수 있었다. (2) 국내 기후의 변화로써 기온의 경우는 기상청 통계자료작성이 시작된 이후 과거에서 현재까지 시간이 흐름에 따라 최대 약 25 %까지 연평균 기온이 상승하였고, 강우량 및 바람의 경우는 시간의 경과에 대해서는 뚜렷한 변화의 경향은 나타나지 않았다. 또한, 강수량의 경우 최저 5.3 mm, 최대 18.9 mm로 나타났으며, 풍속의 경우는 전반적으로 2 m/s 전후의 풍속을 나타내었다. (3) 기온에 의한 작업불능일로 대부분의 작업불능일이 기온이 낮은 11월부터 2월과 기온이 높은 7월부터 8월에 포함되어 있는 것으로 나타났으며, 통계년수에 따른 작업불능일의 변화는 뚜렷한 경향을 나타내지 않았다. 또한, 강우량에 대한 작업불능일로 대부분이 여름철의 강우기인 7월 및 8월에 집중되어있는 것을 확인할 수 있었고, 대체로 최저 25일~최대 37일 사이로 일정 수준의 작업불능일을 유지하고 있음을 확인할 수 있었다. 풍속에 의한 작업불능일은 전체적으로 1일이 채 안되게 산정되었다. (4) 각 통계년수별 작업불능일을 비교한 결과, 서울지역의 경우 통계년수 1년에서는 실외 및 반실내구간이 155일, 실내구간이 133일로 산정되었고, 통계년수 5년에서는 실외 및 반실내구간이 약 174일, 실내구간이 약 139일이 산정되었으며 통계년수 10년에서는 실외 및 반실내구간이 약 159일, 실내구간이 약 131일로 산정되었다. 또한, 통계년수 30년에서는 실외 및 반실내구간이 약 166일, 실내구간이 약 138일로 산정되어 큰 편차는 보이지 않았다. (5) 본 연구에서의 작업불능일 산정 결과를 대한주택공사 기준 및 연구결과와 비교하였을 시 기온에 의한 작업불능일의 경우 서울지역은 43일 및 29일의 차이를 나타내었고, 대구지역은 1일의 매우 근소한 차이를 나타낸 반면에, 부산 및 울산에서는 본 연구와 대한주택공사 기준 및 연구결과와의 차이가 50일 이상으로 나타나 각 작업불능일 수는 지역간의 편차를 심하게 나타내었다. 이는 대한주택공사의 규정, 기존연구결과에서 적용한 규정이 본 연구에서 적용한 규정과 상이하고, 작업불능일 산정을 위한 통계년수가 과거 10년 혹은 30년 자료를 이용함에 따라 기후변동이 충분히 반영되지 않았기 때문에 이러한 차이가 발생된 것으로 사료된다. 또한, 강우량에 의한 작업불능일은 기존 연구결과와의 차이는 4일 이내로 나타났지만, 대한주택공사 기준과는 11일 이상의 많은 차이를 보였는데, 이 역시 적용기준의 차이와 통계년수 결정의 차이에 기인된 결과로 사료된다. 이상을 종합하면, 건설공사 초기 계획단계에서 기후요소에 의한 작업불능일을 산정할 경우 적용 통계자료의 범위로서 최근 1년, 5년, 10년, 30년의 자료를 비교, 분석한 결과 전반적으로 통계년수에 따른 작업불능일은 지구의 온난화와 도시화 등에 기인하여 다소 차이가 있는 것으로 조사되었는데, 이중 작업불능일 산정을 위한 최근 5년에 대한 통계자료는 최근의 기상변동을 보다 정확히 반영할 수 있다는 측면에서 작업불능 산정시 적용의 효용성이 크다고 생각되며, 10년 및 30년의 통계자료와 비교시 자료 수집, 정리, 분석의 어려움 해결, 데이터의 신뢰성 및 기후변화 양상에 적합한 작업불능일의 산정이 가능할 것으로 판단된다. In this paper, the non working days of each region in Korea based on climate data during past 1, 5, 10, and 30 statistical years at the phase of preparing working day scheduling were studied. The regions is included with Seoul, Busan, Daejon, Daegoo, Ulsan, Inchon and Chongju. The calculation was used to produce the most suitable statistical year for estimating non working day. This paper is composed of four chapter. In the first chapter, the objective and background of the study is discussed. In the second chapter, theoretical considerations of work schedule was studied. In the third chapter, the determination of non working days with each region based on climate data for collecting period level was compared and studied. In the final chapter, conclusions of the paper were summarized. The results of the paper are summarized as followings. (1) First, each sector[government and non government] has estimated their own non working days. First, the Korea Housing Corporation's standard specification has classified the nations area by calculating the average temperature and has given 1~6 level regions and also it has given computed number of minimum 15 to maximum of 115 days for winter season's non working[construction] days. Where as, the COE (American Army Corps of Engineers) contract states to divide the Korean land into 16 areas and each area with definition of non working days. As I have looked into the past researches and case studies, each of them listed all different calculation of non working days. (2) The national climate weather temperature has gradually moved up around 25%, however rainfall and wind has not shown much change. In case of rainfall, minimum of 5.3mm and maximum of 18.9mm were recorded and the wind speed was generally recorded around 2 m/s. (3) The most of the non working days were found on November through February effected by low temperature, and July through August was recorded high by the reason of high temperature. There were no clear tendency in change of working days in the statistical year. further more, I came to know that July and August were the month with most non working days by rainfall. Generally, the number of dates recorded from minimum of 25 to maximum of 37 days. Not even one non working day was found effected by wind. (4) As I have compared the non working days of every statistical years, I have found out that, 115 days of non working days were recorded for outdoor and semi indoor of Seoul's one statistical year, the indoor was 133days, and in five statistical year, the outdoor and semi indoor recorded 174days, and indoor was 139days. Further more, in 10 statistical year, outdoor and semi indoor recorded 159days and indoor was 131days. Lastly, the 30 statistical year showed outdoor and semi outdoor of 166days, and indoor recorded 138days which showed no great deviation. (5) This research's and The Korean housing Corporation's statistic on non working days considering the weather factors showed difference of 43 and 29days in seoul, and Dae-Gu showed only one day of difference, while Busan and Ul-san showed about 50 days of difference compared to both statistics. This tells us that there is a high variation through regions. More so, the non working days by rainfall showed 4 day of difference in statistics however, there were over 11days difference compared to the Korean housing Organization (6) As I have applied the statistics of non working days to the field case, total construction day was calculated exactly 1,308days which was two times more the working dates. The working dates needed to be calculated again by preparing construction methods appropriate to the climate. In conclusion, the comparison and analysis of the statistical data of 1 year, 5 years, 10 years and 30 years indicated that if work incapable days by weather factors are calculated at early stage of building construction, the number of days varies widely due to global warming and urbanization etc, and among these data, the statistical data for the recent 5 years are considered effective to be applied in the calculation of work incapable days as they can reflect recent meteorological change accurately, and when compared with 10 years and 30 years statistics data, they would better facilitate data collection, arrangement and analysis with data reliability for climatic change.

섬유 및 수축저감용 혼화제 혼입에 따른 고강도 콘크리트의 기초적 특성 및 내화특성

조만기 청주대학교 일반대학원 2014 국내석사

The objective of this paper is to investigate the effect of the combined use of organic fiber and shrinkage reducing admixtures on the engineering properties and fire endurance performance of the high strength concrete with 50 MPa. Polylon fiber, which was mixed with nylon fiber and polypropylene fiber was applied to achieve spalling prevention performance. Two different shrinkage reducing agents were also used such as emulsified refined cooking oil (ERCO) and glycol based shrinkage reducing agent to reduce autogenous shrinkage. Fire resistance test was conducted in accordance with ISO-834 curve using cylindrical specimen with 100 mm in diameter and 200 mm in length for three hours. The following results could be made as conclusion. (1)For the fundamental properties of fresh concrete, for all the different types of concrete with different W/B, comparing with Plain concrete, slump and flow were little decreased and showed similar flowability with Plain concrete. For the segregation resistance test, for all types of concrete with different W/B, the evaluation index for segregation (EIS) is lower than 2.5 which belongs to level 2. It is considered that all types of concrete with different addition ratio of ERCO showed good workability. (2) For the air content, All types satisfied the target range of 2±1 % and as the adding ERCO's hydrophobic group could be combined with AE component, so the air content was largely reduced. For the high strength concrete, comparing with normal strength concrete, it always with more compact structure which have high resistance for freeze-thaw even with low air content. (3) For the early age compressive strength, comparing with Plain, the strength decreased as addition ratio of fiber and shrinkage reducing agent increased. Whereas for the concrete after curing for 56 days, compressive strength has been generally same with the Plain. All the compressive strength for different types of concrete is identified higher than 80 MPa. For the tensile strength, as different addition ratio of ERCO and SR, tensile strength generally maintained similar or little decreased comparing with Plain. All the types of the tensile strength showed about 10% as same as compressive strength. (4) For the autogenous properties, with different types and addition ratio of agent, autogenous shrinkage substantially decreased with the increased addition ratio of shrinkage reducing agent. When with the same dosage as ERCO, using SR generally performed better effect about reducing autogenous shrinkage than using ERCO. It would be explained as the principal component of aliphatic acid(C3H5(OCOR)3) in ERCO would be reacted with Ca(OH)2 interior the concrete, 2RCOOCa would be generated and fill the capillary pores interior the concrete. As the solid existed in the position of capillary pores, the effect of shrinkage would be relaxed. (5) For the fire resistance, when PF fiber was used, the vapour could emission when PF fiber melt in high temperature and considered as effective for explode resistance. When ERCO was used, all the specimen with different W/B did not exploded and belonged to level 1 for magnitude of explosion which considered as good resistance to the explosion. (6) For the rate of mass reduction, all the specimen with different W/B, the rate of mass reduction is all below 10%, which showed good property for resistance to the explode. For the residual strength after fire, there showed different results about residual strength and residual strength ratio when W/B changed. The specimen showed lower residual strength than Plain which lower than 20%. The correlativity for residual strength ratio when ERCO used was conducted as 0.773 which identified the good effect for using ERCO. From the shpere of this study, properties as flowability and strength has been sufficiently identified when ERCO was used in high strength concrete. Effect of autogenous shrinkage reducing agent has also been proved as the filling effect in the capillary pores interior the concrete. The filling effect in the capillary pores were speculated as play some role for resistance to the explode. As for the conclusion, when ERCO was used in high strength concrete, it showed good effect on resistance to the explosion as well as autogenous shrinkage reduction effect. For the residual strength after fire, comparing with using SR, using ERCO showed higher residual strength ratio, but lower than 20% which could not be used after fire, and further study about increase residual strength is needed.

교육시설의 설계 VE 기법 적용에 관한 사례 연구 : 충북 오송 고등학교를 중심으로

이윤재 청주대학교 대학원 2013 국내석사

우리나라 교육시설은 해방이후 1980년대까지 교육부 표준설계도에 의한 획일적인 학교시설의 양적 팽창의 시기를 거쳐, 1990년대는 새로운 학교의 출현 및 학교 설립 운영 규정의 제정 등을 통한 질적 성장 도모의 시기를 겪었다. 특히, 2000년대부터는 1998년 제7차 교육과정 고시에 따라 단위학교의 교육과정 자율편성 확대와 개별특성과 환경을 고려한 사용자의 다양한 요구를 반영하는 등 사용자 참여중심의 미래지향적 학교건축시기로서 다양한 교육환경을 모색하는 시기로 접어들고 있다.1)2) 2000년대 들어서면서 교육과정 변화에 맞춰 설계과정에 교육청, 사용자 뿐만 아니라 사업자도 포함시켜 설계, 시공 및 시설 유지관리까지 요구함으로서 미래교육환경 변화에 대응하는 적응성 및 융통성을 확보할 수 있는 건축설계방식을 모색하고 있고 이러한 관점에서 민간투자사업(BTL)의 등장, 설계 경제성 검토 등의 선진화된 기법이 도입되고 있는 실정이다. 특히, 최근 들어 신설 및 일부 중고등학교에서는 학생들에게 맞춤형 교과이수를 위해 과목별로 전용 교실을 두고 학생들이 수업 시간표에 따라 교실을 이동하며 수업을 듣는 교과 교실제를 실시하고 있으며, 그 효과가 입증되고 있어 이러한 교과교실제의 확산이 예상되고 있다.3) 그러나 이러한 교과교실제의 도입에 따른 교육시설의 공간 구성 및 배치 등이 계획단계에서부터 충실히 반영되어야 효과적인 교과교실제의 지원이 가능한데, 실제적으로 상당수의 설계업계에서는 교과 교실제에 대한 공간적 이해부족으로 홈베이스 설치 미비, 적절한 복도공간 미흡 등 설계에 어려움을 겪는 것으로 알려져 있다. 특히 발주처인 교육청에서는 시설공사 비용절감에 대한 집중적인 고려로서 계획 및 실시 설계 단계에서 설계 경제성 검토를 요구하고 있음에 교과 교실제를 고려하지 못한 설계 VE검토가 진행될 경우 당초 취지에 부합하지 못하는 설계가 이루어 질 수 있다. 이러한 교과 교실제 대상 교육시설물의 최상의 가치를 얻기 위하여, 설계에 대한 경제성 및 현장적용의 타당성을 여러 전문분야의 협력을 통해 기능별, 대안별로 검토하는 체계적인 프로세스(Systematic Process)가 요구되고 있고, 그 중심에서 적용되고 있는 것으로 설계 Value Engineering(이하 VE)을 들 수 있다. 이러한 VE는 단순한 설계검토나 시공단계의 원가절감만이 아닌 불필요한 기능을 제거하여 대체 안을 개발, 유지시키는 기능 중심적 사고로 접근하여 최적안을 도출하는 활동이며 또한, 시공단계 보다 설계단계에서 이루어지는 것이 공사비용의 절감에 큰 영향을 미친다. 따라서 본 연구에서는 설계단계에서 효율적인 원가절감 및 가치향상을 위한 설계경제성 검토 방법으로서 설계 VE 기법을 교과교실제가 도입된 교육시설에 적용한 사례를 분석하여 시공단계에서의 단순한 원가절감이 아닌 설계단계에서의 VE 적용에 따른 원가절감 및 프로젝트의 최적성을 검토함으로서 대상 시설물의 가치 및 기능향상과 원가를 절감할 수 있는 사례를 제시하고자 한다.

컬러콘크리트 패널의 최적배합비 결정 및 LCC 분석에 의한 경제성 평가

김태청 청주대학교 대학원 2010 국내석사

본 연구에서는 의장성 콘크리트의 다기능화를 추구할 수 있는 컬러콘크리트를 패널 형태로 제작하고자 최적의 성능을 발휘할 수 있는 배합비 및 시공방법을 제시하고, 이를 토대로 LCC 분석과 VE 분석을 실시하여 기존 마감공법과의 경제성을 비교ㆍ분석하였는데, 그 결과를 요약하면 다음과 같다. (1) 컬러콘크리트 패널 제조를 위한 물성평가 결과 착색재 치환율 증가와 레드머드의 소성온도 및 치환율이 증가할수록 응결시간이 단축되는 경향을 보였으며, 플레인과 비교시 적색과 흑색의 경우, 약 1시간 30분 전후로 단축되었고, 황색의 경우 4시간 30분 전후로 단축되는 것으로 나타났으며, 백색 및 녹색은 플레인과 유사한 경향으로 나타났다. (2) 착색재 종류 및 치환율에 따른 압축강도는 적색 및 황색 착색재가 3-6 % 치환될 경우 7, 28일에서는 플레인보다 약간 증가하였고, 치환율 9-12 %에서는 약간 저하하는 경향으로 나타났으며, 백색, 흑색 및 녹색 착색재의 경우 전반적으로 플레인에 비해 저하하는 것을 알 수 있었다. (3) 붉은 색 발현을 위한 경제적 착색재로서 레드머드의 활용 가능성을 평가한 결과 레드머드의 소성온도 변화에 따른 압축강도로서 소성온도가 400 ℃ 증가될 때마다 약 2 MPa씩 증가하는 것으로 나타났으며, 레드머드의 치환율 변화에 따른 압축강도는 치환률 3 % 증가시 약 3 MPa 정도씩 증가하는 것으로 분석되었다. (4) 착색재 치환율에 따른 발색도는 착색재 치환율 6 %에서 가장 양호한 성능을 갖는 것으로 나타났으며, 특히 붉은색 발현을 위한 레드머드의 경우를 소성온도 800 ℃ 및 치환율 6 %에서 가장 양호한 성능을 발휘하는 것으로 나타났다. (5) 붉은색을 발현하는 컬러콘크리트 패널의 제조를 위한 배합조건으로서 착색재는 소성온도 800 ℃로 소성된 레드머드를 6 % 치환하는 것이 가장 양호한 결과를 얻었으며 타설방법은 이동평형 타설식과 수직 타설식을 병행하여 제조하였고, 이 경우 발색도는 L*값 63.6, a*값 23.9, b*값 28.5로 나타났으며, 육안상 얼룩, 긁힘, 평활도 및 품질에 있어서 모두 만족하는 것으로 나타났다. 또한 외벽 마감재로써 적용 가능한 컬러콘크리트 패널의 시공방법은 석재시공의 건식공법 중 일반적인 앵글 긴결공법으로 시공하는 것이 적정하다고 판단된다. (6) 컬러콘크리트 패널의 LCC 분석을 통한 경제성을 평가한 결과, 초기투자비용은 컬러콘크리트와 비교시 12,217 원/m² 절감되었고, 일반페인트에 비해 62,185 원/m² 높게 분석되었으나, 유지관리비용은 컬러콘크리트와 일반페인트 마감에 비해 약 30,000 원/m² 정도 절감되는 것으로 확인할 수 있었다. 또한, 총 LCC 비용은 컬러콘크리트에 비해 약 40,000 원/m² 정도 절감되었고, 일반페인보다는 약 32,000 원/m² 정도 증가되는 것으로 분석되었다. (7) 컬러 콘크리트패널의 VE 분석을 통한 성능평가 결과 일반페인트 마감이 상대 LCC 점수가 가장 우수하게 나타났으나, 성능점수에서 컬러콘크리트 패널이 크게 나타나 성능측면을 고려한 성능점수와 가격측면을 고려한 LCC점수를 복합고려한 종합적인 가치점수로는 컬러콘크리트 패널이 가장 우수한 것으로 분석되어 LCC 대비 성능분석에서 가장 양호한 방법은 컬러 콘크리트 패널공법임을 알 수 있었다. The objective of this study is to present the optimum mixture proportion of concrete considering efficiency and economic aspects when the color concrete, generating decorative multi-functional uses, is made into panel. In addition, Life Cycle Cost(LCC) of the color concrete panel was analyzed and compared with existing color concrete placement method and painting method to verify the economic benefits of the color concrete panel. The results of this study were summarized as follows. (1) As for determining optimum mixture proportion, the setting time of color concrete panel has decreased or at least remain the same as the increase of pigment replacement ration and soldering temperature of red mud. Compared with the plain mixture, the red and the black has shown 1 hour and 30 minute decrease in time and the yellow, 4 and 30 minute as such. Meanwhile, the white and the green remain the same as the plain. (2) The compressive strength has slightly gone up and down compared the plain. The red and the yellow pigment replacement of 3-6% has it slightly go up compared to the plain at 7th and 28th day and those of 9-12%, same or slightly go down. However, the white, the black, and the green shows that it is going down slightly compared to the plain. (3) The analysis of the red mud applicability as the color representation pigment shows that the compression strength as per the red mud sintering temperature has increased by 2MPa, in every 400?? increase and by 3MPa in every 3% replacement ratio increase. (4) The color representation as per the pigment replacement ratio has shown that the effect is at maximum at 6%, In case of the red mud, at soldering temperature of 800?? and the replacement ratio of 6%. (5) As for the red color representation effect of the color manufacturing, the optimum combination of factors are of soldering temperature at 800?? and with the replacement ratio of 6%. The fabricating method is executed with the combination of horizontal and vertical methods. The color representation of such method shows that L* 63.6, a* 23.9, b* 28.5. The qualities in regard to stain and scratch and flatness are all satisfactory when it being observed with naked eyes. The applicable construction method of the color concrete panel will be angle-fracture fixation with the use of the tension wire among the stone method. (6) The result from the economic evaluation through the LCC analysis on the color concrete panel has shown that the initial investment cost has gone down by KRW 12,217/m² compared to the color concrete and up by KRW 62,185/m² compared to the general paint, while maintenance cost, down by KRW 30,000/m² compared to both the plain and the paint. The total LCC cost has decreased by KRW 40,000/m² compared to the color concrete and increased by KRW 32,000/m² compared to the general paint. (7) The functional analysis through VE method indicates that comparative LCC value of general paint finish is excellent. However, the overall value point of color concrete is the highest with the excellent functional value and its cost factor of the color concrete. So the color concrete panel construction method is proved to be the most cost efficient from the LCC analysis.

저온 조건에서 타설된 콘크리트의 보온 양생법 개발

손호정 청주대학교 대학원 2013 국내박사

최근 건설공기의 중요성이 강조 됨에 따라 연중시공이 필수화 되어 기온이 낮은 겨울철에 시공이 불가피한 실정이다. 겨울철 공사에는 한중 콘크리트 시공이 적용되는데, 한중 콘크리트란 콘크리트를 부어넣은 후의 양생기간에 콘크리트가 동결할 염려가 있는 경우에 시공되는 콘크리트를 의미 하는 것으로 기온이 낮은 시기에 콘크리트를 타설 할 경우 타설 초기에 콘크리트의 동결에 따른 초기 동해가 발생되고, 응결 및 경화 지연에 따른 강도 발현이 저하 하는 등의 문제점이 생기게 된다. 1)2)3) 현재 국내·외 건설공사 현장에서는 저온 조건에서 콘크리트의 피해를 감소시키기 위한 방안으로 소정의 재령에서 설계기준 강도가 얻어지도록 강도를 보정하거나, 제트히터, 갈탄, 열선 및 발열패널 등을 이용한 가열보온양생, 부직포, PE필름, 톱밥 등 보양재를 활용하여 구조체 자체의 수화열만으로 콘크리트를 양생하여 소요 강도를 발휘하는 단열보온 양생 등 다양한 방법을 채택하여 효율적인 현장 관리가 이루어지고 있는 상황이다. 또한, 이와 관련하여 국내·외 많은 연구진들에 의하여 한중 기간 콘크리트의 품질 확보를 위한 다양한 연구가 진행되고 있다. 특히 한6) 등은 비닐막에 공기층을 적층한 버블시트를 이용하여 한중 환경에서 콘크리트의 초기동해 방지 및 소요강도 발휘가 가능한 단열보온양생 공법을 개발하여 건설 현장에서 널리 활용되고 있고, 국내 D사에서는 열선을 콘크리트 내부에 매설하여 직접 가열하는 기술을 개발한바 있다. 그러나 이러한 기술들은 일평균 기온이 낮지 않은 지역에 국한되어 있는 실정이다. 2013년 1월 기상청 통계자료를 살펴보면 서울을 비롯한 강원도 산간지역의 경우는 이상 기온에 따른 기후 변화에 기인하여 일평균기온이 -10℃이하로 저하되는 기간이 증가되고 있고, 철원 및 대관령 지역의 경우에는 최저기온이 -20℃ 이하로 매우 낮은 저온 환경에 처하게 된다. 또한, 국내뿐만 아니라 러시아 및 카자흐스탄 등 기온이 매우 낮은 것으로 잘 알려진 국가에서도 마찬가지로 저온 환경에서는 일반적인 가열 및 단열보온양생법에 의한 콘크리트의 양생 효과를 기대하기가 어렵고 효율적인 관리가 이루어지지 않고 있어 낮은 기온조건을 대상으로 한 콘크리트 구조물의 효율적인 품질관리가 필요한 실정이다. 따라서, 본 연구에서는 하루평균 기온이 -10℃ 전후의 저온 조건에서 타설 되는 콘크리트의 효율적인 보온양생법 제안을 목적으로 양생온도 -10℃ 정온 조건에서 콘크리트 부재 중 가장 취약한 슬래브 및 벽체 부재를 상정한 모의부재를 제작하여, 단열 및 가열 보온 양생법 변화에 따른 콘크리트의 제반온도이력과 강도 발현특성을 분석하고자 한다. 또한, 이를 토대로 온도이력 해석 프로그램을 통해 최적 보온양생법의 양생성능 결과와 실제 실험 데이터를 비교분석하여 정합성을 검토한 후 실구조체 적용을 위한 Mock-up test를 실시하여 저온 조건에서 시공되는 콘크리트 구조물의 초기동해방지 및 품질확보를 위한 최적 보온양생법을 제안하고자 한다.