干湿交替作用下受弯开裂钢筋混凝土梁内氯离子侵蚀特性

Study on chloride penetration into flexural cracked reinforced concrete beams subjected to drying-wetting cycles

为了研究干湿交替条件下受弯开裂混凝土内氯离子侵蚀机理及其分析方法,对两两自锚并保持开裂状态下的混凝土梁进行氯盐溶液干湿循环试验。借助15和30次干湿循环的两次取样结果,分析完好截面、裂缝截面及其周围一定范围内的自由氯离子含量分布规律,并对提出的等效氯离子扩散模型的适用性、弯曲裂缝宽度的影响规律以及扩散系数的时变特性等问题进行探讨。研究结果表明:1氯盐干湿交替作用下,开裂截面处的表层对流区深度在10~20mm之间,弯曲裂缝的存在将加快混凝土内部氯离子的渗透速度;2裂缝周围混凝土内的氯离子传输受到裂缝(】0.1mm)及混凝土弯曲拉应力的共同影响,当与裂缝距离增大时,混凝土弯曲拉应力对氯离子传输的影响也会增大;3拟合结合表明,当裂缝宽度w【0.30mm时,用等效扩散模型分析开裂截面的氯离子含量分布是可行的,且等效氯离子扩散系数的劣化特性可用w的多项式函数进行回归分析;4对普通混凝土而言,氯离子扩散系数的时间衰减指数m与水灰比有关,且随水灰比的减小而减小。

In order to study the mechanism of chloride penetration in flexural cracked concrete under the drying-wetting cycles,drying-wetting cycle tests were carried on several self-anchored cracked reinforced concrete( RC) beams. Based on the experimental results obtained after 15 and 30 cycles respectively,the free chloride concentration profiles at different sections of sound and cracked concretes were presented and analyzed. The applicability of the established equivalent diffusion model,influence of crack width on chloride diffusion and time-dependent diffusion coefficient were discussed.Following conclusion can be concluded:(1) With chloride drying-wetting cycles,the depth of surface convection region in cracked concrete beams is between 10 mm and 20 mm,and the chloride penetration speed will be increased by cracks;(2)Chloride penetration in concrete around flexural cracks will be influenced by both cracks(> 0. 1mm) and tensile stress of concrete. And the effect of tensile stress will increase with the distance from crack section;(3) The equivalent diffusion model is suitable for analyzing the chloride penetration in flexural cracked concrete when thesurface crack width is less than 0. 3mm. And the relationship between crack width and equivalent diffusion coefficient can be described with polynomial function of crack effect;(4) For ordinary Portland concrete( OPC),the age-related degradation exponent m is related to the ratio of water to cement( W / C),and it will become smaller with the decrease of W / C.