The Temperature Crack Control Of Mass Concrete Pier Base

This paper is based on the construction of Lizigou Bridge on the Neijiang-Kunming Railway, which consists of 7X32m simple supported beams, 72+3X 128 + 72m continuous rigid-frame composite-beam and 8X32 simple supported beams. There are such characteristics as deep base, high pier, large span and long combination in this bridge. The bridge' s pile caps are mass concrete structures and have mass concrete' s inherent characteristics, the biggest one of which is 37. 6X18. lX5m. That is, after concrete is poured, its temperature rapidly rises because of hydration heat,then, with reduction of hydration heat and transpiration of concrete interal heat to external medium, will drop to a steady temperature, at the same time, its volume firstly expands and then shrinks. During temperature rise of concrete, if the difference between internal temperature and external one is very large, the external concrete will bear very large tensile stress. During temperature drop of concrete, because concrete' s shinkage is restrainted by base rock, it will bear tensile stress too. If these tensile stresses are larger than concrete' s ultimate tensile strength at the same age, they can lead to concrete' s temperature crack. Temperature crack will decrease bearing capacity and durability of pile caps, and cause safety hidden trouble of bridges.especially to over 100 meters high pier, the crack' s harm is serious. So it is necessary to do a study of scheme on temperature control of the bridge' s mass concrete pile caps.1. The paper expatiates on the harm and formation mechanism of temperature crack in mass concrete structure, demonstrates the feasibility of preventing temperature crack.2. On the base of discussing heate conduction equation and the calculating method of concrete internal temperature field as well as effect factors of it, an approach is put forward which is available to reduce concrete internal maximum temperature, to control it' s temperature difference between interior and exterior and to prevent it' s temperature from vary rapidly.3. Basing on the bridge' s practical things, a series of temperature control measures are designed. The effect by excuting it indicates that it is successful.