预应力混凝土箱梁水化热裂缝控制与预防

Control and Precaution the Early Cracks of Hydration Heat in PC Box Girder Bridges

目前大跨预应力混凝土箱梁桥的早期开裂现象较为普遍,已成为桥梁工程界极为重视的重大技术问题。水化热是引起混凝土箱梁早期裂缝主要原因之一。以某箱梁桥水化热实测数据为基础,探讨不同配合比条件下水化热对箱梁混凝土早期开裂的影响,结果表明:过高的水化热是引起箱梁腹板早期开裂的主要原因之一,实际施工可在混凝土中掺入适量粉煤灰,以减少水泥用量从而降低混凝土的水化热,就该桥测试数据而言,掺入了18%的粉煤灰可显著的降低箱梁混凝土水化热的影响。大跨预应力混凝土箱梁桥施工早期应采取有效措施使结构的内外温差控制在30℃以内。

At present,the early cracks phenomena of long-span prestressed concrete box girder is common,which have come to bridge engineers attention.Hydration heat is one of the main reasons for early cracks.Based on the temperature field of PC box girder with different concrete proportion during hydration,the results demonstrated that hydration heat was one of the main reasons which caused the early cracks in the web of box girder.In addition,Adding appropriate amount of fly ash in concrete can reduce the dosage of cement concrete so as to reduce the hydration heat,based on the test data,mixed with 18% of fly ash can significantly reduce the influence of the hydration heat concrete box girder.Effective measures should be taken to control the temperature difference between the inside and the surface less than 30 ℃.