유화처리 정제식용유를 이용한 고강도 콘크리트의 자기수축 저감

김태청 청주대학교 2013 국내박사

High strength concrete has many advantages, but one drawback of this material is the high risk of autogenous shrinkage that has to be mitigated before applying to field construction. There are a number of commercial products that can mitigate this problem, such as expansive agent and shrinkage reduction agent. However, these commercial products are relatively expensive and thereby cannot be affordable in many practices. In addition, for the shrinkage reduction agent, it is originally made for the reduction of drying shrinkage and not for the reduction of autogenous shrinkage. In previous study, it was found that small amounts of plant oil adding to concrete significantly reduced autogenous shrinkage. This previous study demonstrated that the effect of the oil on reducing the autogenous shrinkage was attributed to filling the capillary pores in concrete. Although the addition of oil had such an advantage in high strength concrete, it caused the dramatic decrease of slump in fresh concrete and compressive strength in hardened concrete. Therefore, this current study continues investigating the effect of oil on reducing autogenous shrinkage and focuses on how to solve the problem (slump reduction and strength reduction) of the oil found in the previous work. The new technique to provide the solution that can offset the deteriorated properties of concrete is to emulsify the oil, which is expected to improve its dispersion performance. To examine the new emulsified oil, this study investigates the effect of the emulsified oil on the fundamental and autogenous shrinkage properties of concrete and compared its result with the effect conventional shrinkage reduction agent. Based on the results, this study proposed an economically effective mitigation method for autogenous shrinkage of high strength concrete. The key findings drawn from this study are summarized as follows. (1) For the properties of high strength mortar with emulsified Refined cooking oil (ERCO), unlike Refined cooking oil, ERCO significantly improves the slump of fresh concrete, which is similar to the control concrete without oil. This improvement of fresh concrete with ERCO of 1% by cement weight can solve the problem that is once raised by the concretes with conventional shrinkage reduction agent and Refined cooking oil. (2) For the strength properties of mortar, the addition of conventional shrinkage reduction agent and wast cooking oil decreases the compressive strength. However, the addition of ERCO of 1% by cement weight improves the strength higher than that of control concrete at early age and similar to that of control concrete at 28 days. (3) For the results obtained from a porocemetry test, it is found that the addition of ERCO dramatically reduces the porosity of cement paste. This is arising from the chemical reaction of between ERCO and the hydrates of calcium hydroxide and filling the pores in the cement paste. In addition, the test results obtained from SEM, it is found that micro-structures of the cement paste with ERCO is more dense than that of control cement paste. (4) For the autogenous shrinkage of mortar, it is found that ERCO in a mortar specimen is the most effective on reducing autogenous shrinkage. As compared with other mortar specimens, ERCO reduces autogenous shrinkage up to 60% as compared to control mortar and up to 40% as compared to the mortar with conventional shrinkage reduction agent. Again, this is attributed to the fact that the oil reacts with the hydrates of calcium hydroxide in concrete and as a result, filling the capillary pores. This effect can result in the release of shrinkage pressure. (5) For the properties of high strength concrete with ERCO, slump results are similar to the results of control concrete. However, ERCO with more than 2% by cement weight significantly decreases the slump of fresh concrete so that the content of ERCO should be minimum. For the results of compressive strength tests, ERCO can solve the problem arising from the use of ordinary cooking oil. In addition these results with ERCO are better than that of conventional shrinkage reduction agent. Hence, ERCO of 1% by cement weight in concrete is recommended. (6) Addition of ERCO results in good slump flow, which similar to the results of control concrete, regardless of water to cement ratio. In addition, ERCO has similar results of air content to control concrete, but delays up to 2 hours in setting time, compared to control concrete. For the strength properties, the addition of ERCO causes the slight reduction. For autogenous shrinkage, the w/b of 0.15 concrete with ERCO reduces up to 32%, compared to control concrete, and the w/b of 0.20 concrete with ERCO reduces up to 33%. In addition, the w/b of 0.25 concrete with ERCO reduces autogenous shrinkage up to 23%. These results obtained from all concretes with ERCO are more effective than conventional shrinkage reduction agent. In conclusion, this study demonstrates that the addition of ERCO used for the reduction of autogenous shrinkage maintains the fundamental properties of concrete such as slump, air content and setting time (similar level to control concrete without oil). Therefore, it is expected that the new proposed ERCO can replace the conventional shrinkage reduction agent for reducing autogenous shrinkage of high strength concrete.

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.