毛细作用下硫酸钠半浸泡水泥基材料抗氯离子渗透性研究

硫酸盐和氯盐复杂盐蚀环境中的服役结构会受到两者产生的耦合作用。研究毛细作用下硫酸钠半浸泡混凝土试样的抗氯离子渗透性能，设计不同水灰比、不同硫酸钠溶液浓度的砂浆毛细上升试验，测试硫酸钠半浸泡混凝土试样的扫描电镜（SEM）、X射线衍射（XRD）和氯离子电通量。结果表明：硫酸钠半浸泡混凝土抗氯离子渗透性能劣化，前期劣化严重，随着半浸泡时间的延长，抗氯离子渗透性能有所回升，但依然比未浸泡试样的差。结合微观测试结果可知，混凝土抗氯离子渗透性能劣化的主要原因是：前期，在毛细作用下硫酸钠溶液填充了混凝土孔隙，减弱了固化氯离子的结合能力，释放了较多自由氯离子，从而增大了氯离子的扩散量；后期，随着浸泡时间的延长和环境湿度的变化，孔隙中的硫酸钠溶液过饱和后，形成无水Na₂SO₄和Na₂SO₄·10H₂O结晶体的混合物，结晶混合物沉淀于孔壁，部分阻碍了氯离子的扩散，从而减缓了抗氯离子渗透性能的劣化。硫酸钠溶液浓度超过5%以后，随着硫酸钠溶液浓度的升高，毛细上升速度减缓，混凝土抗氯离子渗透性能相应提高。硫酸钠溶液半浸泡下，水泥基材料毛细上升快慢可作为衡量混凝土抗氯离子渗透性能好坏的指标。硫酸钠和氯化钠的复合溶液对硫酸钠毛细上升有延缓作用，会改善混凝土的抗氯离子渗透性能。

Chloride penetration resistance of cementitious materials half-submerged in sodium sulfate solution under capillary suction

The service structure in the complex salt etch environment of sulfate and chloride may be affected by the coupling effect of them. In this paper, the chloride penetration resistance (CPR) of the concrete half immersion in sodium sulfate solution (SSS) under capillary action is studied. The capillary rising test of mortar with different water-cement ratio and different concentration of SSS was designed. Scanning electron microscopy(SEM), X-ray diffraction (XRD) and electric flux of chloride ion are applied to the concrete half immersion in SSS. The results show that the CPRs of concrete samples half immersion in SSS deteriorates, and have obvious degradations at early stage, but recover a bit at later stage. Combined with the results from microscopic tests, the degradations are attributed to the SSSs filled in the pores of concrete samples. The SSS impairs the ability of bound chloride ion and releases more free chloride ions, which increases the electric flux of chloride ion. With the extension of soaking time and the change of the relative humidity of environment, supersaturate SSS comes into being Na₂SO₄ and Na₂SO₄·10H₂O crystals. The admixtures of crystals deposit on the walls of pores, and partially hinder the diffusions of chloride ions, hence increase the CPRs. When the concentration of SSS is higher than 5 percent, the velocity of capillary suction (VCS) slows down and the CPR of concrete is accordingly enhanced with the increase of the concentration of SSS. The VCS can be used to predict the CPR of concrete. The mixed solutions with sodium sulfate and sodium chloride can retard the VCS and then improve the CPR for concrete.