疲劳荷载与氯盐耦合作用下混凝土中氯离子扩散行为的试验研究

混凝土桥梁在服役过程中经常同时承受疲劳荷载和氯离子侵蚀,但现有研究多未考虑疲劳和氯离子侵蚀的耦合作用。本文研究了疲劳荷载与氯盐侵蚀耦合作用下混凝土中氯离子的扩散行为,并运用超声检测表征混凝土的疲劳损伤,以建立疲劳损伤与氯离子扩散性能之间的关系。研究结果表明:随着疲劳压应力水平提高,超声参数表征的混凝土损伤值也逐渐增大;应力水平低于0.4时,不同疲劳应力水平对混凝土中氯离子浓度分布没有明显影响,氯离子扩散系数甚至略有减小,这应是应力水平较低时混凝土中微孔隙和裂缝被压缩而降低了氯离子的扩散能力;应力水平为0.5及0.6时,混凝土中氯离子浓度显著提高,扩散系数明显增大,并且与应力水平呈正相关;超声参数表征的混凝土损伤与氯离子渗透性的发展趋势不一致,表明由于混凝土内部缺陷分布的不均匀性使得超声技术难以定量表征荷载引起的混凝土损伤。

Experimental Study on Diffusion Behavior of Chlorine Ion in Concrete Subjected to Fatigue Loading

Reinforced concrete bridges are often subjected to fatigue loads and chloride ion erosion in service.However very few investigations were carried out to study the combined action of fatigue loads and chloride penetration.In the present paper the transfer of chloride ion in concrete subjected to fatigue loading was studied,and the damage of concrete induced by fatigue loads was determined by ultrasonic.Then the relationship between fatigue damage of concrete and the chloride ion permeability was established.The results showed that the damage value of concrete reflected by ultrasonic parameters gradually increases as fatigue stress levels (applied to concrete) increase.When fatigue stress levels are less than 0.4,the distribution of chloride ion in concrete shows no significant differences under different stress levels,and the chloride diffusion coefficient decreases slightly,which should be due to compaction of micropore and microcrack under relative low fatigue stress level.While the stress level is increased to 0.5 or 0.6,the concentration of chloride ions in concrete grows obviously,and the chloride diffusion coefficient increased significantly,positively correlated with stress level.The concrete damage characterized by ultrasonic parameters is inconsistent with the chloride ion permeability with increase in fatigue numbers,which shows that ultrasonic has limitations to quantitatively characterize the damage induced by loads due to non-uniform distribution of defects in concrete.