碳酸水溶液环境里氯离子在水泥基材料中的迁移

Migration of Chloride Ions in Cement-based Materials in Carbonic Acid Solution Environment

当地下水含较高浓度的碳酸和氯离子时,碳酸水溶液对地下混凝土结构的腐蚀会导致氯离子在混凝土中的迁移更快。本工作研究了碳酸水溶液环境里氯离子在砂浆中的迁移特性,用X射线衍射分析(XRD)、热重分析(TG-DTG)和扫描电子显微镜(SEM-EDS)分析了碳酸水溶液-氯离子侵蚀下净浆侵蚀产物以及微观形貌的变化。结果表明:碳酸水溶液侵蚀前期,氢氧化钙和水化硅酸钙(C-S-H)凝胶脱钙碳化生成碳酸钙填充了砂浆的孔隙结构,抑制了氯离子在砂浆中的迁移;侵蚀后期,由于碳酸钙的溶解以及低钙硅比的C-S-H凝胶转变为无定型硅胶共同导致了砂浆孔隙率增大,氯离子在砂浆中的迁移加快;碳酸水溶液侵蚀导致了水泥基材料中Friedel’s盐的分解以及C-S-H凝胶吸附氯离子能力的下降;降低水灰比能增加砂浆抗碳酸水溶液侵蚀能力及降低氯离子的迁移速度。

When the groundwater contains a high concentration of carbonate and chloride ions,the corrosion of carbonic acid solution on underground concrete structures will lead to a faster migration of chloride ions in concrete.Migration characteristic of chloride ions in mortar exists in carbonic acid solution environment.The corrosion products and microstructure of paste under the attack of carbonic acid solution and chloride ions were analyzed by X-ray diffraction(XRD),thermogravimetric analysis(TG-DTG)and scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS).The results show that in the early stage of carbonic acid water corrosion,calcium hydroxide and C-S-H gel decalcifies to form calcium carbonate filling the pore structure of the mortar,and inhibits the migration of chloride ions in the mortar.At the later stage of corrosion,the dissolution of calcium carbonate and the conversion of C-S-H gel with a low calcium-silicon ratio into amorphous silica gel lead to the increase of mortar porosity and the acceleration of chloride ion migration in mortar.Carbonic acid water corrosion results in the decomposition of Friedel's salts and the decrease of the adsorption capacity of C-S-H gel for chloride ions.Reducing water-cement ratio can increase the corrosion resistance of mortar to carbonic acid water and reduce the migration rate of chloride ions.