Mechanistic Study of Failure of Concrete Subjected to Cyclic Thermal Loads.

摘要

This project was aimed at understanding the behavior of normal weight concrete subjected to cyclic thermal loading. It includes experimental and analytical work with emphasis on thermal strain incompatibilities between cement paste and aggregates due to different coefficients of thermal expansion. The report describes a study to investigate mechanisms which lead to fatigue failure of concrete pavement surfaces due to their repeated exposure to the hot exhaust gases of the auxiliary power unit (APU) of F/A-18 aircraft. The experimental results show a degradation of the microstructure and the mechanical properties with thermal cycling. Analytical modeling was used to calculate temperature and stress distributions in a concrete which is heated on the surface by a hot air stream. From the analysis and discussion of the results, a hypothesis for a heat fatigue failure mechanism was developed. This mechanism is the creation and propagation of microcracks in the concrete. The cracks are mostly caused by drying shrinkage and lead to a scaling of the concrete surface. Four methods are proposed to modify concretes to achieve a better heat resistance when exposed to thermal cycling.