山区公路桥梁在役护栏混凝土劣化机理

Deterioration Mechanism of Guardrail Concrete Served for Highway Bridge in Mountainous Areas

摘要:

为探明贵州山区公路桥梁服役期间护栏混凝土的劣化成因，以某建成通车数年的高速公路桥梁为研究对象，分别从护栏典型破坏区域与完好区域钻取混凝土芯样，开展碳化深度、氯离子含量、骨料碱活性等宏观性能测试，并结合微观形貌与孔结构特征分析，揭示护栏混凝土的劣化机理。结果表明：典型破坏区域混凝土浅层（0~5 mm）界面结构疏松，水化硅酸钙（C-S-H）凝胶较少，且多害孔（d>200 nm）与有害孔（50 nm≤d≤200 nm）数量明显多于完好区域；两个区域在0~35 mm深度范围内均检出氯离子，表明除冰盐已渗透至混凝土内部；碳化作用与骨料碱活性对本次劣化影响较小。综合判断，盐冻破坏是导致护栏混凝土劣化的主要原因。除冰盐与融冰形成的盐溶液侵入混凝土后，在冻融循环作用下造成界面结构与孔结构破坏，致使混凝土表面开裂、剥落。此外，机制砂混凝土在成型过程中易发生离析泌水，进一步加重了盐冻破坏的不利影响。

Abstract:

To investigate the causes of deterioration in guardrail concrete during the service life of highway bridges in Guizhou’s mountainous areas， a highway bridge that had been in operation for several years was selected as the research subject. Concrete core samples were drilled from both the typical deteriorated areas and the intact areas of the guardrail. Macroscopic performance tests， including carbonation depth， chloride ion content， and aggregate alkali activity， were conducted. Meanwhile， the deterioration mechanism of the guardrail concrete was revealed by combining the analysis of micro-morphology and pore structure characteristics. The results indicate that in the shallow surface layer （0-5 mm） of the concrete in the typical deteriorated areas， the interfacial structure is loose， with less calcium silicate hydrate （C-S-H） gel present. The number of harmful pores （d>200 nm） and less harmful pores （50 nm≤d≤200 nm） is significantly higher than in the intact areas. Chloride ions were detected in both areas within the depth range of 0-35 mm， indicating that deicing salt had penetrated the concrete interior. Carbonation and aggregate alkali activity have a minor impact on this deterioration. It is comprehensively determined that salt-frost scaling is the primary cause of the guardrail concrete deterioration. After the deicing salt and the salt solution formed by melting ice infiltrated the concrete， the interfacial structure and pore structure are damaged under the action of freeze-thaw cycles， leading to surface cracking and spalling of the concrete. Furthermore， the manufactured sand concrete is prone to segregation and bleeding during the forming process， which exacerbates the adverse effects of salt-frost scaling.