横向弯曲裂缝对混凝土内氯离子侵蚀作用的影响

Influence of Transverse Flexural Crack on Chloride Penetration in Concrete

分析了横向开裂混凝土内氯离子的侵入机理及其主要影响因素，建立了基于双重孔隙介质模型的修正Fick定律氯离子扩散模型，并对持续加载下的开裂钢筋混凝土梁构件进行了氯盐干湿循环侵蚀试验。试验采用浓度为5%的NaCl溶液，在进行15个干湿循环后，借助快速氯离子含量检测RCT（Rapid Chloride Testing）法，对各裂缝处不同深度的氯离子含量进行了测定。试验结果表明：1）干湿循环侵蚀作用下，开裂混凝土表层0~20 mm范围内氯离子含量出现峰值，故可取表层对流区深度为15~20 mm左右；2）当表面裂缝宽度小于0.3 mm时，等效氯离子扩散系数平稳增大，模型的预测精度较高；当裂缝宽度大于0.3 mm后，等效氯离子扩散系数快速增大，氯离子侵入受对流作用的影响加大；3）受弯开裂混凝土等效氯离子扩散系数的劣化因子与裂缝宽度有直接关系，建议采用二次幂函数或分段函数来进行描述。

The mechanism for chloride penetration in cracked concrete and its major impact factors were analyzed. As a result, a revised chloride diffusion model based on Fick＇s Law was built by dual porous medium model. Then several cracked reinforced concrete beams self-anchored with sustained flexural loads were immersed in the 5% NaCl solution with the condition of dry-wet cycles. After 15 times of dry-wet cycles, the rapid chloride testing （RCT） was used for the determination of chloride ion content of the powder at each cracked sections. The test results show that： 1） with the condition of dry-wet cycles, the chloride content will occur a peak in the surface 20mm concrete, so the depth for surface convection zone can be assumed to be 15~20 mm; 2） when the crack width is less than 0.3mm, the equivalent chloride diffusion coefficient increases steadily, which agrees well with model＇s prediction; when the crack width is larger than 0.3mm, the equivalent chloride diffusion coefficient augments rapidly and influence of convection on chloride penetration becomes more significant; 3） the deterioration factor for equivalent chloride diffusion coefficient in flexural cracked concrete is directly correlative with crack width, which can be expressed by second order power function or separate function.