Thermal Analysis and Practical Construction Method for the Hydration-Induced Crack Control of Underground Concrete Box Structures

Recently, massive concrete structures are increasingly built in Korea. In such massive structures, the heat of hydration may cause cracking problems. The reinforced concrete box structures are classified in this category that needs much attention to control the hydration heat problem due to restraining effects on the boundaries. The present study focuses on the development of rational construction method to control the thermal stress problem of the box structures. The major variables for the analysis and test are the length (L) and height (H) of concrete wall for one-time placement and the cement content of concrete mixtures. The temperatures at various points of test walls are automatically measured according to the time after placement. The analysis results agree well with measured data. It is seen that the reduction of cement content exhibits more effects in reducing temperatures and thus thermal stresses. The ratio of L/H for concrete placement affects the thermal stresses, but the effect is rather small for L/H greater than certain values, i.e. 5. The present study indicates that the crack inducing joint should be deep enough to induce cracks appropriately. The results of present study may be efficiently used for the practical design and construction of reinforced concrete box structures, especially to countermeasure the hydration heat problem of mass concrete.