热疲劳作用对高性能混凝土强度的影响机理研究

夏季日照辐射下，跨江、跨海混凝土桥墩的表面温度很高，在水流冲刷或溅射时，混凝土表面遭受冷热循环的热疲劳作用而性能发生变化。通过模拟跨江、跨海混凝土桥墩遭受的热疲劳作用，研究高性能混凝土抗压强度、劈裂抗拉强度、孔结构及微观形貌的变化规律，并分析强度变化的机理。结果表明，HPC40和HPC60抗压强度与抗拉强度均随热疲劳次数的增加呈先增后减的趋势，且无论强度增或减，高强度高性能混凝土的变化都更明显。高性能混凝土内基体孔结构呈先细化后粗化的变化规律，导致基体微结构先增强后劣化。在热疲劳作用前期，高性能混凝土强度提高是由于未水化胶凝材料再水化对基体的增强作用；在后期，基体与骨料之间热学差异引起不协调变形导致的界面过渡区劣化，加之基体微结构劣化，共同作用导致了强度下降。

Study on the mechanism of thermal fatigue cycling on strength of high performance concrete

In summer, the surface temperature of concrete piers across rivers and sea is very high under the radiation of sunlight. When the flow scours or sputters, the performance of the concrete changes subjected to the thermal fatigue of cold and hot circulation on surface. Based on this, by simulating the thermal fatigue function of the marine environment, the influence of thermal fatigue on the compressive strength, splitting tensile strength, pore structure and morphology is studied, and the action mechanism is analyzed. The results show that the compressive and tensile strength of HPC40 and HPC60 increase first and then decrease with the increase of thermal fatigue cycles, and whether the strength increases or decreases, the change of HPC with high grade strength is more obvious. The pore structure of HPC matrix is refined first and then coarsened, leading to the matrix microstructure becoming loose from dense. In the early stage of thermal fatigue cycling, the reinforcement of the matrix by rehydration of the unhydrated cementitious material is the main reason for strength enhancement. However, in the later stage, the deterioration of the interfacial transition zone due to uncoordinated deformation caused by thermal differences between the hardened cement matrix and the aggregate, combined with the deterioration of the matrix microstructure, causes a decrease in strength.