气泡特征对混凝土抗盐冻性能的影响

摘要

采用快冻法研究了普通混凝土(OPC)、引气混凝土(APC)和高性能混凝土(HPC)在质量分数为3.5％的NaCl溶液中的抗盐冻性能,并借助低真空扫描电子显微镜(SEM)观测了水泥浆体中气泡特征,研究了混凝土气孔结构对混凝土抗盐冻性能的影响规律.结果表明:在水胶比0.50的OPC浆体中,引入直径小于30 μm、间距小于60 μm,且均匀、独立分布的密闭气泡可以显著提高OPC的抗盐冻性能；对于强度等级C40的HPC,气泡结构是影响混凝土抗盐冻性能的主要因素,掺加引气剂、获得优异的气泡结构是提高其抗盐冻性能的有效途径；对于掺硅粉的HPC,当水胶比小于0.31时,气泡结构特征不再是影响其抗盐冻性的主要因素,即使不添加引气剂,这种混凝土也具有较高的抗盐冻性能.%The salt frost resistance and air void parameters with ordinary Portland concrete (OPC), air-entrained Portland concrete (APC) and high performance concrete (HPC) subjected to the action of 3. 5% (in mass fraction) sodium chloride (NaCl) solution were studied by the accelerated freezing-thawing method. The air-bubble characteristic was examined through scanning electron microscopy (SEM). The results show that the diameter is less than 30 μm, the spacing factor is less than 60 μm, and independent distribution of the sealed air-bubble can significantly improve the salt frost resistance of the OPC with water-binder ratio of 0. 50; for C40 of the HPC, the air-bubble structure is a major factor for salt frost resistance; adding air entraining agent to obtain excellent air-bubble structure is the effective means for improving salt frost resistance of concrete. Adding silica fume, water-binder ratio is less than 0. 31 for HPC, air-bubble structure characteristic is not a major factor for salt frost resistance, this concrete has higher salt frost resistance, even without adding air-entraining agents.