预应力混凝土结构多尺度多因素耦合的耐久性研究

Under the coupling behavior of carbonation and chloride corrosion, prestressed concrete structures could be degraded and collapsed eventually. Usually the micro-scale material durability and macro-scale structural durability are investigated independently by traditional analysis methods. Therefore, even now the unified model to predict the durability of prestressed concrete structure, which can be used to connect micro-scale analysis to macro-scale analysis, was not successfully developed. Moreover, the traditional prediction models based on the coupling influences of multi-factors were mostly based on Fick's law and experimental data regressing. However, these models neglected the dissolution process of CO2 and chloride in aqueous solutions in porous concrete. Furthermore, these models did not consider the non-ideality of the systems, in which the corrosive materials are of high concentrations in the test chamber. Therefore, it was difficult for them to observe the accurate corrosion mechanism of coupling behavior for carbonation and chloride attack essentially and it was even more difficult for them to predict the durability performance reasonably. In this project, two "bridges" will be built: one is the thermodynamic model, by which the coupling behaviors of micro-scales and multi-factors can be combined; the other one is to construct the relationship between the micro-scale durability indices (e.g. carbonation depth, carbonation degree and chloride ion concentration predicted by the thermodynamic model) and the macro-scale material strength and strain. On the basis of these relationships, the micro-scale analysis results can be directly used for the macro-scale structural analysis. Finally, it is expected that the prediction model which couples multi-scales with multi-factors of durability of prestressed concrete structure can be developed.

在碳化和氯离子等因素耦合作用下，预应力砼结构功能会逐渐衰退，最终耐久性失效。传统研究方法通常将微观尺度的材料耐久性和宏观尺度的结构耐久性独立进行研究，未开发出连接微观到宏观尺度的一体化预应力砼结构耐久性预测模型；且传统多因素耦合研究多是根据Fick定律，通过回归试验数据而建立的，既忽略CO2和氯盐在砼孔隙水溶液中的溶解过程，也忽略了试验箱中侵蚀物质高浓度带来的体系非理想性，因而不易准确考察砼碳化和氯离子侵蚀耦合作用机理及实现耐久性的准确预测。本项目研究拟建造两座"桥梁"：第一座桥梁是化工热力学模型，通过它可以将微观尺度多侵蚀因素作用关联起来；第二座桥梁是拟建立的微观尺度耐久性指标（例如热力学模型预测的碳化深度、碳化程度、氯离子浓度等）与宏观结构材料的强度、应变之间的关系，通过它可以实现微观尺度研究结果直接用于宏观结构分析。从而，最终实现构建多尺度多因素耦合的预应力砼结构耐久性预测模型。

耐久性是混凝土材料的重要性能之一，它涉及混凝土结构或构筑物的服役寿命和使用安全。但耐久性问题涉及面广、实际服役环境复杂、多因素耦合试验缺乏、现有理论不够完善，故本项目针对四个方面开展了多尺度、多因素耐久性问题的理论分析、试验研究及精细化数值模拟。.在混凝土及预应力混凝土结构冻融机理及耐久性评估中，材料试验发现：随着细观冻融损伤的增长，混凝土的宏观抗压强度呈三段式下降；在预应力构件试验中，建议寒冷地区轴心预应力构件的冻融预应力损失的取值不小于5%；在有限元模拟分析研究中，开发了一套混凝土细、宏观冻融损伤的模拟程序，给出了冻融寿命预测的建议方法 。.在对混凝土碳化过程的精细化数值模拟研究中，从化学反应动力学的角度出发，建立了偏微分方程组，并基于骨料级配理论和孔隙概率密度函数，用ABAQUS模拟了二氧化碳在混凝土中的扩散。.在对普通混凝土结构受氯盐侵蚀的耐久性试验研究中，开展模拟浸没区、浪溅区以及大气区 的复合氯盐侵蚀试验，研究不同工况、不同氯盐侵蚀对混凝土耐久性的影响。.在对氯盐侵蚀自密实混凝土过程的精细化数值模拟与试验研究中，首先，分别进行了氯盐溶液浸泡、氯盐盐雾侵蚀和RCM法测氯离子扩散系数试验。然后对不同龄期的自密实混凝土的氯离子扩散系数进行预测。最后，建立偏微分方程组，并通过ABAQUS二次开发和MATLAB计算，实现了氯盐侵蚀自密实混凝土的多尺度精细化数值化模型。