低载疲劳损伤RC结构氯环境下腐蚀机理及剩余疲劳寿命试验

The mechanical performance of reinforced concrete (RC) bridge structures in coastal or in deicing environment will be deteriorated by comprehensively action of service cyclic load and chloride environment. The damage of RC structures by fatigue loading will be accumulated (cracks developed, stiffness and ductility deteriorated). Because the chlorideion is liable to get to steel bars through macrocrack and microcosmic of damaged concrete, the steel bar would rusted early and the fatigue life of the RC bridge structures reduced. Under normal service condition, amplitude of fatigue loading are lower (10%-40% ultimate load), the chloride permeation and corrosion mechanism of fatigue damaged structures were not clear yet. The working condition of RC bridge structures in coastal environment is simulated here, the chloride permeation and corrosion mechanism in fatigue damaged structures are experimental investigated, where RC structures were pre-damaged in different level by fatigue loading and then the damaged structures suffered environment action of chloride corrosion. The fatigue life of such damaged structures will be studied. The chloride permeation and corrosion mechanism of fatigue damaged structures would be compared with the structures damaged by monotonic loading. The assessment model of fatigue durability and prediction model of fatigue life for damaged RC structures in chloride environment will be suggested. The achievement of the researching project will supply technical reference for fatigue durability assessment and fatigue life prediction of concrete structures.

沿海（或除冰）环境的钢筋混凝土(RC)桥梁结构受到疲劳荷载和氯环境的综合作用.疲劳荷载使RC结构损伤累积（裂缝扩展、刚度和延性劣化），氯离子易于通过损伤混凝土的宏观裂缝和微观裂隙侵入并到达钢筋，导致钢筋过早锈蚀和结构疲劳寿命缩短。正常使用条件下疲劳荷载幅值较低（10%-40%极限荷载）,低载损伤RC结构的氯扩散性、钢筋腐蚀机理和疲劳寿命尚不清楚。本项目模拟沿海环境RC桥梁结构的工作状态，试验研究低载疲劳损伤RC结构在海水干湿循环过程中氯传输规律和钢筋腐蚀机理;研究不同程度疲劳损伤RC结构经历海水干湿循环作用后的疲劳寿命,比较疲劳损伤RC结构氯渗透和钢筋氯腐蚀状态与单调荷载损伤结构的差异，研究疲劳损伤RC结构疲劳耐久性评估方法。为沿海及除冰环境下混凝土结构的疲劳耐久性评估和提高结构疲劳耐久性提供科学依据。

氯（沿海或除冰盐）环境下钢筋混凝土（Reinforced Concrete, RC）桥梁结构受到疲劳损伤和氯侵蚀的综合作用，其疲劳性能劣化规律和机理尚不清楚。 .通过40个RC梁试件试验，研究疲劳损伤RC梁氯腐蚀后的剩余疲劳性能和混凝土氯扩散规律，采用荷载水平（疲劳荷载上限与极限强度之比，分别取0.2、0.3、0.4、0.45）和循环加载次数（分别取1、5、20、40、80、120万次）表征初始疲劳损伤程度；将疲劳损伤RC梁置于3.5 wt. %NaCl溶液干湿循环环境6个月（或3个月）实现氯腐蚀过程。还试验研究了坑蚀钢筋和不同配筋率（1.06%、1.59%和2.91%）RC梁的疲劳寿命。研究取得以下重要结果，初始疲劳损伤RC梁氯腐蚀后的剩余疲劳性能仍符合典型的三阶段发展特征，即快速发展、稳定发展和突然破坏；增加初始疲劳损伤程度会加速RC梁剩余疲劳性能劣化及氯扩散；与加载次数相比，荷载水平对氯扩散和剩余疲劳性能的影响更显著。当配筋率为1.59%时RC梁剩余疲劳寿命最长，配筋率为1.59%和2.91%（77%界限配筋率）时在疲劳加载后期均呈现明显的非线性特征。基于试验结果研究提出了考虑等效表面缺陷的坑蚀钢筋疲劳寿命预测模型、基于Fick第二定律建立了疲劳损伤RC梁氯扩散模型和剩余使用寿命预测模型，提出了剩余疲劳寿命和使用寿命关系，进而提出了剩余疲劳寿命预测模型，且模型计算值与试验结果吻合良好。.研究成果发表论文16篇，其中SCI期刊论文8篇。培养硕士和博士研究生6人。研究成果可为氯环境下RC桥梁疲劳耐久性提供科学依据。