斜拉桥桥塔承台大体积混凝土水化热仿真分析与裂缝控制

Hydration Heat Simulation and Crack Control of Mass Concrete of Pylon Base Slab of Cable-stayed bridge

以某斜拉桥桥塔承台大体积混凝土为工程背景,通过数值仿真分析研究探讨了大体积混凝土水化热阶段承台结构的温度场及应力场分布情况。研究表明:大体积混凝土水化放热阶段温度变化非常显著,普通硅酸盐水泥混凝土内、外部温差在浇筑4 d后达到最大随后稳步下降,而低热水泥混凝土内、外部温差在浇筑混凝土8 d后达到最大。混凝土的水泥及粉煤灰含量对放热效应影响最为显著,水泥含量越高、粉煤灰含量越低,放热效应越明显,内、外部温差越大;相比较而言,相同级配及分层浇筑方式下,低热水泥混凝土的最大温升、内外温差和混凝土表层温度均较普通硅酸盐水泥有所降低。混凝土水化放热阶段应力变化极为显著,普通硅酸盐水泥混凝土最大拉应力浇筑3~4 d达到峰值,而低热水泥混凝土在浇筑7 d达到峰值;在承台倒角斜面内及冷水管的空当部位拉应力集中现象非常明显,极易超过允许拉应力,从而产生表面裂缝,现场可通过优化混凝土配合比、控制混凝土入模温度、增加表层混凝土保温措施、控制混凝土的浇筑间隔与分层厚度、调节通水时间、控制进水流量与温度、延缓带模蓄水养护时间等措施来有效防止。

Taking the mass concrete of pylon base slab of a cable-stayed bridge as the engineering background, the article studies and discusses the temperature field and stress field distribution of base slab structure in the hydration heat stage of mass concrete through the numerical simulation analysis. The study results show that the temperature variation in the hydration heat stage of mass concrete is very obvious, the temperature difference between the inside and outside of ordinary Portland cement concrete will be maximum after 4 d pouring and soon afterwards go down steadily, and the temperature difference between the inside and outside of low-heat cement concrete will be maximum after 8 d concrete pouring. The cement and fly ash contents of concrete will most obviously affect the heating effect. The higher is the cement content, and the lower is the fly ash content. The more obvious is the heating effect, the larger is the temperature difference between the inside and outside. In comparison, the maximum temperature rise, inside and outside temperature difference, and the concrete surface temperature are lower than the ordinary Portland cement under the same grading and layering pouring mode. The stress variation in the concrete hydration heating stage is extremely obvious. The maximum tension stress of ordinary Portland cement concrete will reach the peak value after 3 ～4 d concrete pouring. And the low heat cement concrete will reach the peak value after 7 d pouring. The concentration phenomenon of tension stress is very obvious within the chamfer of base slab and at the open space of cold water pipe, and very easily exceeds the permitted tension stress so as to cause the surface cracks. The cracks can be effectively prevented by the on-site optimization of concrete mixing proportion, control of concrete casting temperature, increment of surface concrete insulation measure, control of concrete pouring interval and layer thickness, adjustment of water running time, control of influent flow and temperature, and delay of curing time with water.