地铁车站大体积混凝土底板早期减缩防裂措施研究

Research on early shrinkage reduction and crack prevention measures of mass concrete floors in subway stations

混凝土早期收缩是导致地铁车站混凝土底板内部产生早期应力的主要原因之一。首先通过试验的方法获取底板配比混凝土收缩曲线,以及在底板配比基础上改变减水剂掺量或胶凝材料中粉煤灰掺量的混凝土收缩曲线。然后通过有限元模拟分析的方法探究底板内部等效龄期与收缩应力的变化规律及其相互关系,结果表明:受水化反应正反馈机制影响,底板内部的等效龄期和收缩应力均高于底板的上部和下部;适当地减少减水剂掺量和加强早期保湿养护能够在一定程度上减少底板的早期收缩。

The early shrinkage of concrete is one of the main causes for early stress in the concrete floors of metro stations.Firstly,through the method of testing,the shrinkage curve of proportioned concrete in the bottom board is obtained,as well as the shrinkage curve of concrete by changing the amount of water reducing agent or fly ash in the cementitious material on the basis of the mixing proportion of the bottom board.Then,the variation rules and relationship between the equivalent age and shrinkage stress in the bottom board are analyzed through the finite element simulation analysis method,and the results show that under the effect of a positive feedback mechanism of hydration reaction,the equivalent age and shrinkage stress in the bottom board are higher than those in the upper and lower parts of the bottom board.The appropriate reduction of the amount of water reducing agent and strengthening of early moisturizing and curing can decrease the early shrinkage of the bottom board to a certain extent.