大体积承台混凝土早期表面开裂控制措施

针对大体积混凝土浇筑时因水化热作用引起的早期表面开裂问题,对比分析浇筑温度、环境温度、保温材料以及位移约束条件4种因素对混凝土表面应力的影响程度.以宁波象山港公路大桥承台为实例建立有限元模型,选取6个开裂关键部位的节点,分析这些节点的应力数值在28d龄期内随4种影响因素变化的规律.模拟分析分层浇筑和水管冷却2种降温措施对于减小混凝土表面拉应力的作用.结果表明,混凝土表面拉应力与浇筑温度呈正比,与环境温度呈反比;保温层对承台表面中心部位拉应力的影响大于边缘部位;提高模板的刚度对抗裂有利;分层浇筑和水管冷却可以不同程度地改善表面开裂状况.

Control measures for preventing crack on the surface of mass concrete abutment in early stage

In order to prevent surface crack of massive concrete caused by hydration heat in early stage of concreting, the effects of four parameters, i.e., concreting temperature, environmental temperature, material of insulating layer, and constraint conditions on surface stress were analyzed. Finite element analysis was done by taking an abutment of Xiangshan harbor highway bridge in Ningbo as an example. Six points in the key cracking area were selected, and the change of surface stress on these points under the independent effects of four parameters over 28 days period was analyzed. Moreover, two methods for temperature reduction, layer by layer concreting and pipe cooling, were simulated and their effects on surface tensile stress were also examined. The result reveals that, tensile stress on the surface of concrete is proportional to concreting temperature while inversely proportional to environmental temperature; heat preservation reduces surface tensile stress more efficiently in the central area than at the edge of abutment; increasing stiffness of concrete formwork is beneficial to crack prevention; layer by layer concreting and pipe cooling prevent surface crack in different degree.