掺氧化镁混凝土建造高碾压混凝土重力坝的温度补偿计算方法

本文探讨了大坝混凝土掺氧化镁后温度徐变应力的变化规律,建立了考虑温度历时效应的氧化镁微膨胀混凝土仿真计算方法,计算中考虑了温度对混凝土自生体积变形的影响,严格按照混凝土龄期和温度场的分布状况,选取与之相对应的自生体积变形增量。并以一工程为实例,比较了坝体混凝土掺或不掺氧化镁的温度徐变应力的不同。得出的结论认为,在大体积混凝土内部,掺氧化镁能够起到补偿温度应力的作用,但是,对靠近边界部位的混凝土,由于混凝土表面一定范围内的温度梯度较大,加之边界周边环境因素的影响,如没有采取有效的表面保护措施,将会引起局部膨胀量的不一致,从而削弱掺氧化镁的补偿作用,甚至有可能增加局部混凝土的拉应力,引起早期表面裂缝。

Study on thermal compensation method for high RCC dam constructed with the admixture of MgO

In this paper the difference between the thermal creep stresses of concrete adding MgO and without MgO is investigated. A thermal compensation method which takes into account of the slight time-dependent expansion in concrete due to MgO is put forward. The autogenous volume change in correspondence with the different ages and distribution of temperature field is simulated in a rigorous way so as to reflect the effect of temperature. An application of the method for one project helps cast a light on the issues related to use of MgO in hydraulic structures of concrete. The stress compensation effect of MgO at different locations of concrete dams is also discussed. The concrete near the surface of dam, due to higher temperature gradient may cause surface cracks. Therefore surface protection measures are needed. The conclusions may act as a reference in future design and construction of dams.