Study on the Reduction of Thermal Crack of Mass Concrete

Abstract

The purpose of this study was the performance evaluation of Urea mixed concrete appropriating for mass concrete of high-rise building and quantitative analysis of hydration and calory of cement. Slump, Adiabatic temperature rise, Compressive, Drying shrinkage and Thermal conductivity tests were performed. And TG/DTA, Calorimeter tests for micro analysis of cement hydration were performed. Using experiment results, FEM analysis was performed. As results of Slump test, use of mixing water could be reduced as Urea mixed. In Adiabatic temperature test, initial and maximum temperature of concrete were decreased 0.29℃, 0.33℃ as Urea 1% mixed. And reaching time were delayed 2.67 hours as Urea 1% mixed. Compressive strength were reaching the design strength except Urea 7% mixed. As results of Drying shrinkage test, drying shrinkage was decreased as Urea mixed. In Thermal conductivity test, Urea was not affect to thermal conductivity. As results of TG/DTA test, Ca(OH)2 decreased 0.23%. In Calorimeter test, calorie of cement was reduced as Urea mixed. Lastly, as result of FEM analysis using experiment results, maximum temperature of concrete are decreased 0.97℃ and reaching time to maximum temperature delayed 1.86 hours as Urea 1% mixed. In case of thermal crack index, thermal crack index increased 0.13 and lowest point was delayed 2 hours as Urea 1% mixed.|최근 건축물의 대형화 및 장대화로 인하여 매스부재의 사용이 증가하고 있다. 이에 따라 온도균열 저감에 관한 연구들이 활발히 진행되고 있으나, 비용대비 성능미흡, 공정의 복잡화로 인한 공기지연 등 해결해야 할 다양한 문제점들이 발생되고 있다. 최근 Urea의 흡열 반응을 이용한 온도균열 저감에 관한 연구가 진행되고 있으며, Urea 혼입 콘크리트는 수화온도 저감, 건조수축 저감, 장기 강도에서 압축강도 회복 등의 다양한 성능이 나타나는 것으로 보고되고 있다. 하지만 기존 연구는 대부분 해외에서 진행되었으며 국내에서의 연구는 미미한 실정이다. 또한 기존 Urea 혼입 콘크리트 관련된 연구는 콘크리트 물성평가에 관한 연구만 진행되었으며 미세분석, FEM해석에 관한 연구는 전무한 실정이다. 따라서 본 연구에서는 초고층화에 적합한 매스콘크리트 압축강도 30Mpa 콘크리트의 물성평가를 실시하고, TG/DTA, Calorimeter 시험을 통해 온도 및 강도 특성에 관한 정량평가를 실시하고자 한다. 또한 단열온도상승시험, 압축강도시험 결과를 토대로 실제 구조물 크기의 매스콘크리트에서 Urea 혼입율에 따른 온도균열지수의 변화에 관한 해석적 평가를 실시하고자 한다. 단열온도상승시험결과, Urea 1%당 타설 온도는 0.29℃, 최고온도는 0.33℃ 저감되며 최고온도 도달시간은 2.67시간 지연되는 것으로 나타났다. 압축강도는 7, 28일에서 강도저하가 나타나나 재령일이 길어짐에 따라 강도회복특성이 나타났으며, 슬럼프 시험결과 배합방법에 의한 단위수량 저감 뿐만 아니라 타설 온도 저감으로 인해 추가적인 단위수량 저감이 가능하다. 건조수축시험 결과, Urea 혼입에 따라 최대 21% 저감되었으며 열전도율은 Urea 혼입에 따른 변화는 나타나지 않았다. TG/DTA 미세분석 결과 Ca(OH)2소비와 CaCO3의 생성에 관한 정량평가를 실시할 수 있었으며, Calorimeter 시험 결과 최대 20%의 열량 저감이 가능한 것으로 나타났다. 또한 FEM 해석 결과, Urea 1%당 최고온도는 0.97℃ 저감 최고온도 도달시간은 1.86시간 지연되었으며 온도균열지수는 0.13 상승하여 Urea 혼입 콘크리트가 콘크리트 안정성 측면에서 유리하다.; The purpose of this study was the performance evaluation of Urea mixed concrete appropriating for mass concrete of high-rise building and quantitative analysis of hydration and calory of cement. Slump, Adiabatic temperature rise, Compressive, Drying shrinkage and Thermal conductivity tests were performed. And TG/DTA, Calorimeter tests for micro analysis of cement hydration were performed. Using experiment results, FEM analysis was performed. As results of Slump test, use of mixing water could be reduced as Urea mixed. In Adiabatic temperature test, initial and maximum temperature of concrete were decreased 0.29℃, 0.33℃ as Urea 1% mixed. And reaching time were delayed 2.67 hours as Urea 1% mixed. Compressive strength were reaching the design strength except Urea 7% mixed. As results of Drying shrinkage test, drying shrinkage was decreased as Urea mixed. In Thermal conductivity test, Urea was not affect to thermal conductivity. As results of TG/DTA test, Ca(OH)2 decreased 0.23%. In Calorimeter test, calorie of cement was reduced as Urea mixed. Lastly, as result of FEM analysis using experiment results, maximum temperature of concrete are decreased 0.97℃ and reaching time to maximum temperature delayed 1.86 hours as Urea 1% mixed. In case of thermal crack index, thermal crack index increased 0.13 and lowest point was delayed 2 hours as Urea 1% mixed.