高性能混凝土约束收缩对氯离子扩散的影响

对粉煤灰和矿渣粉双掺总量占胶凝材料总质量的百分比分别为30%，40%和50%及掺合比例分别为1∶2，2∶3和1∶1的高性能混凝土进行了平板收缩试验和快速氯离子扩散系数测定（RCM法）试验，分析了高性能混凝土有约束和无约束收缩开裂性能及对氯离子扩散系数的影响规律。研究结果表明:无约束的混凝土平板均未发生开裂，有约束的混凝土平板基本开裂，双掺矿物掺合料显著改善了混凝土的抗裂性能，当粉煤灰和矿渣粉的掺合比例为1∶1时，其抗裂性能最好，且随着掺量的增加，混凝土的抗裂性越好；矿物掺合料双掺总量和掺合比例一定时，各配比约束收缩混凝土的等效氯离子扩散系数均高于无约束收缩混凝土的氯离子扩散系数，即约束收缩增大了混凝土的氯离子扩散系数，收缩应变越大，混凝土的抗氯离子性能越差；当粉煤灰和矿渣粉掺合比例为1∶1时，约束收缩对混凝土内氯离子扩散的影响最小。

Influence of Constrained Shrinkage Cracking on Chloride Ion Diffusivity of High Performance Concrete

Plate shrinkage test and fast chloride diffusion coefficient test (RCM method) of high performance concrete with total amount of fly ash (FA) and granulated blast furnace slag (GGBFS) of 30%,40% and 50% by mass of binder and ratio of FA to GGBFS 1∶2, 2∶3 and 1∶1 were carried out. The constrained and unconstrained shrinkage cracking behavior of high performance concrete and its influence on chloride diffusion coefficient were analyzed. The results show that the unconstrained concrete slabs have no cracks, and the constrained concrete slabs all crack. The crack resistance of concrete is significantly improved by mixing FA and GGBFS. The crack resistance is best when the mixing ratio of FA and GGBFS is 1∶1. With the increase of FA and GGBFS dosage, the crack resistance of concrete is better. The equivalent chloride ion diffusion coefficient of constrained concrete is higher than that of unconstrained concrete with the same total amount of FA and GGBFS and ratio of FA to GGBFS. The constraint shrinkage crack increases the concrete chloride ion diffusion coefficient. The concrete chloride ion resistance is getting worse with the increase of concrete shrinkage strain. When mixing ratio of FA and GGBFS is 1∶1, the influence of constraint shrinkage of concrete on chloride ion diffusion is minimal.