高性能混凝土在环境热疲劳作用下的性能演化机理研究

The surface of concrete used in bridge pier in the river or sea, high speed railway track plates that exposed to natural environment has a high temperature under the effect of solar radiation in summer; however, the temperature drops significantly when the concrete is subjected to water splashing or rain pouring. This phenomenon results in the hot-cold-temperature cycling in concrete, and it is the environmental thermal fatigue effect. The fatigue stress caused by the alternating action of temperature and humidity leads to the deterioration of concrete performance. This project is proposed to study the influence of thermal fatigue on different strength classes of high performance concrete, and the environmental thermal fatigue experiments would be carried out. The variation of mechanical properties and permeability of high performance concrete under thermal fatigue would be studied considering the influence of composing material and slurry ratio. The damage evaluation index and material failure criterion would be put forward based on the above results. The temperature and humidity distributions of concrete during the process of thermal fatigue would be established by combining the experiment results and theoretical analysis. The stress induced by temperature, humidity gradient and uncoordinated deformation of transition zone would be used as the parameter to establish micro-damage model considering the uncoordinated deformation characteristics of the interface transition zone. The variation of microstructure of harden cement paste and interfacial transition zone under thermal fatigue would be studied through TEM, MIP, nanoindentation and other tests. Moreover, the microscopic mechanism of the mechanical and permeability properties evolution of high performance concrete under thermal fatigue environment would be revealed. The results of the research can provide a theoretical basis for the durability design of concrete structures serving in thermal fatigue environment.

跨江跨海混凝土桥墩、暴露的高速铁路轨道板等混凝土结构，夏季在日照辐射作用下表面温度很高，当受到水流的溅射或雨水的浇淋作用时，表面温度急剧下降，产生冷热循环的环境热疲劳作用。这种温、湿度交变作用使混凝土内部产生疲劳应力，引起混凝土性能的劣化。本研究针对不同强度等级高性能混凝土，通过模拟环境热疲劳试验，研究组成材料和浆集比对热疲劳作用下高性能混凝土力学性能与渗透性能的影响规律，并提出损伤评定指标与材料失效判据；试验与理论分析相结合，研究热疲劳作用过程混凝土内温、湿度场分布规律，并结合界面过渡区不协调变形特征，建立以温、湿度梯度引起的应力和过渡区不协调变形引起的应力为参数的微观损伤模型；通过TEM、MIP、纳米压痕等试验，研究热疲劳作用下水泥石和界面过渡区微结构变化规律，揭示热疲劳环境下高性能混凝土力学性能和渗透性能演化的微观机理。研究成果可为热疲劳环境下服役混凝土结构的耐久性设计提供理论依据。

跨江跨海混凝土桥墩、暴露的高速铁路轨道板等混凝土结构，夏季在日照辐射作用下表面温度很高，当受到水流的溅射或雨水的浇淋作用时，表面温度急剧下降，产生冷热循环的环境热疲劳作用。这种温、湿度交变作用使混凝土内部产生疲劳应力，引起混凝土性能的劣化。本研究针对不同强度等级高性能混凝土，通过模拟环境热疲劳试验，研究了组成材料和浆集比对热疲劳作用下高性能混凝土力学性能与渗透性能的影响规律，并提出了损伤评定指标与材料失效判据；试验与理论分析相结合，研究了热疲劳作用过程混凝土内温、湿度场分布规律，并结合界面过渡区不协调变形特征，建立了以温、湿度梯度引起的应力和过渡区不协调变形引起的应力为参数的微观损伤模型；采用纳米压痕、孔结构等微观试验，研究了微结构的演化规律，结合理论分析，揭示了基体和界面过渡区微结构变化的微观机理；在此基础上，考虑内部温度的演化特征，阐明了高性能混凝土在环境热疲劳作用下的性能演化机理。