冻融环境中ECC/钢复合桥面结构疲劳性能退化机理研究

Domestic application of orthotropic steel box girder bridge is increasing rapidly in recent years. It is a difficult problem for the fatigue cracking of bridge deck pavement leads to premature failure under the repeated action of environment and wheel load. Freezing and thawing environment in Inner Mongolia and the northern part of China accelerates the deterioration of pavement. The durability of bridge deck pavement is seriously insufficient. ECC shows a good application prospect as a new engineering material with ultra high toughness, high tensile strength, excellent crack resistance and it possess good frost resistance and anti fatigue performance. Based on the previous research results, this project intends to study the durability of ECC in steel deck pavement according to the durability characteristics of steel deck pavement in cold region. This project will study the anti fatigue performance of PVA fiber /ECC matrix interface, ECC material, ECC/ steel composite beam structure in the freeze-thaw environment. The research methods of multi-scale model test, nanoindentation, digital image correlation technique and theory analysis are combined. The degradation law of ECC/ steel composite bridge deck structure with the number of freeze-thaw cycles is analyzed. The fatigue performance degradation model of ECC/ steel composite bridge deck structure is established. The degradation mechanism of fatigue performance of ECC/ steel composite bridge deck structure in freeze-thaw environment is studied deeply. It can provide the basis for the design of steel deck pavement ECC in cold area. The service life of the steel deck pavement will be greatly improved.

近些年，正交异性钢箱梁桥在国内应用迅速增加，钢桥面铺装层在环境和车轮荷载反复作用下出现疲劳开裂，服役期内过早产生破坏是当前面临的难题。内蒙古及北方寒冷地区冻融环境加速了铺装层的劣化，钢桥面铺装层耐久性存在严重不足。ECC是一种新型工程材料，具有韧性好、抗拉强度高、控制裂缝能力强、耐冻融、耐疲劳等优点，有很好的应用前景。本项目以前期研究成果为基础，拟采用ECC材料作为钢桥面铺装层，研究PVA纤维/ECC基体界面、ECC材料、ECC/钢复合梁构件三种不同尺度模型在冻融环境中的抗疲劳性能，并结合纳米压痕测试、数字图像相关技术、理论计算等研究手段，分析ECC/钢复合桥面结构疲劳性能随冻融循环次数的退化规律，建立冻融环境中ECC/钢复合桥面结构疲劳性能退化模型，深入研究冻融环境中ECC/钢复合桥面结构疲劳性能退化机理，为寒冷地区钢桥面ECC铺装层设计提供依据，有望提高钢桥面铺装层使用寿命。

该项目按原计划对冻融环境中ECC/钢复合桥面结构疲劳性能退化机理展开研究，先后进行了单纤维拉拔、对ECC梁式试件及ECC/钢复合梁试件冻融、ECC/钢复合梁试件斜剪以及弯曲疲劳试验，结合扫描电镜及DIC数字图像相关技术，对ECC/钢复合桥面结构随冻融循环次数的退化规律进行初步研究。进行了单根PVA纤维的拔出试验。以不同埋置深度与不同埋置角度为研究参数共进行了6组试验，将试验得到的曲线整合分析并将其于理论曲线对比，得到了一组适用于各种拉拔条件下反应PVA纤维/ECC基体界面粘黏结性能的细观参数；随后通过冻融及疲劳试验，发现随冻融次数的增加，PVA-ECC 抗折强度与刚度降低，且荷载-挠度曲线越为光滑最大荷载挠度与残余挠度以及挠度差随时间逐渐增长，且增长速率随冻融次数增加而增加，弯曲刚度随时间逐渐下降，下降速率随冻融次数增加而增加，且PVA-ECC多缝开裂与裂缝无害化处理能力的弱化；进而利用DIC对分析斜剪试验过程中试件的位移场及应变场，结果显示盐冻循环会降低PVA-ECC抗剪强度，导致铺装层中应力集中现象出现在粘性阶段中期。综合上述结果，本研究为寒冷地区钢桥面ECC铺装层设计提供依据，有望提高钢桥面铺装层使用寿命。