A Study on Quality Characteristics of Urea Mixing Concrete considered with Thermal Stress and Drying Shrinkage

온도응력과 건조수축을 고려한 요소혼입 콘크리트의 품질특성에 관한 연구

Due to a big difference of temperatures between the inside and outside and a high level of hydration heat on the core, some thermal stress is generated in mass Concrete. In turn, it causes the expansion of the concrete members and some cracks of the concrete joints that become the factors threatening the soundness of a concrete structure. Due to the reason, various kinds of low-heat concrete are being developed in domestic and foreign countries. In this study, some urea for industrial use which is used in microorganism cultivation agents, etc., is applied as a concrete mixing material in order to suppress the hydration heat of mass concrete. This is intended to lower down some levels of hydration heat and drying shrinkage of mass concrete. 21 kinds of concrete mixtures in total were designed at 3 kinds of W/B ratios, that is, 45, 50 and 55%. Thus, the dynamic characteristics, durability and hydration heat properties of urea-mixed concrete were verified through some experiments and the optimum mixing design was suggested. As the results of this study, the compressive strength of urea-mixed concrete at the age of 3 days decreased by 40% compared to that of plain concrete, but it showed the tendency recovering up to 95% at maximum at the age of 56days. On the other hand, the maximum temperature of urea-mixed concrete decreased down to $7.9^{\circ}C$ at maximum thanks to the hydration heat compared with that of plain concrete and the point of time reaching the highest temperature of the urea-mixed concrete was delayed by 33.9 hours at maximum compared with that of plain concrete. In addition, it resulted that the length change rate of urea-mixed concrete decreased down to 56% at maximum thanks to the expansion characteristics of $CaCO_3$.