干湿循环下氯盐对现浇混凝土硫酸盐腐蚀劣化及扩散影响

Influence of Chloride-Sulfate Attack on Degradation and Sulfate Diffusion of Cast-in-Situ Concrete Structures Subjected to Wet-Dry Cycles

盐渍土地区地表及地下现浇混凝土结构往往遭受多离子-干湿交替的复合侵蚀作用.利用室内试验条件模拟实际工程中地下现浇混凝土结构复合侵蚀过程.测定了试件的尺寸、质量、抗压强度变化及硫酸盐在不同深度的分布情况,进一步采用SEM(扫描电子显微镜)、XRD(X射线衍射)及EDS(电子能谱测试)观察了混凝土试样微观结构及物相变化,并对比和分析了干湿循环条件下氯盐对硫酸盐在现浇混凝土中扩散规律的影响.结果发现,干湿及氯盐影响下现浇混凝土硫酸盐侵蚀更为剧烈,干湿条件下复合侵蚀的混凝土试样在腐蚀后期强度显著降低,氯盐影响下现浇混凝土中硫酸盐的扩散和积累速度更快.研究表明,干湿交替下氯盐对硫酸盐腐蚀存在协同加速效应,氯盐促进了硫酸盐在现浇混凝土中的扩散及积累.

Cast-in-situ underground concrete structures suffer from both sulfate and sulfate-chloride attack and are also affected by alternate drying-wetting conditions.Concrete specimens were manufactured and immersed in sulfate and sulfate-chloride solutions.The wetting-drying tests of concrete specimens were also considered.The size and weight changes were recorded and the compressive strength tests were conducted.The sulfate concentrations in concrete after different immersion period were measured.The SEM,XRD, and EDS were also conducted and analyzed to reveal the degradation mechanism of concrete.The results show that the existence of chlorides accelerates the degradation of concrete caused by sulfate attack and the situation becomes ever worse after wet-dry cycles.The strength of concrete specimens immersed in sulfate-chloride solutions,experiencing wet-dry cycles,suffers from remarkable decline.Chloride has a positive effect on accelerating the diffusion and the accumulation of sulfates in specimens subjected to composite attack,especially in the condition of alternative wet-dry cycles.The degradation of cast-in-situ concrete due to sulfate attack can be accelerated by the existence of chlorides.The chloride ions,in the condition of alternative wet-dry cycles, accelerate the diffusion and the accumulation of sulfate ions in concrete.