Crack Propagation of Ceramsite Lightweight Concrete Under Four-Point Bending Fatigue Conditions

The examination of crack propagation in concrete under fatigue conditions is crucial for comprehending the mechanisms of concrete fatigue failure. Variations in aggregate types result in notable differences in the fatigue crack propagation characteristics of lightweight concrete compared to ordinary concrete. Consequently, this research focused on analyzing the locations and angles of cracks in ceramsite lightweight concrete subjected to four-point bending fatigue conditions, while accounting for different levels of fatigue loading (i.e., stress levels). Furthermore, the study aimed to clarify the influence of ceramsite size and content on the fatigue crack propagation behavior in ceramsite lightweight concrete. The results indicated that an increase in the replacement rate of 5-10 mm and 10-20 mm ceramsite led to the highest probability of fatigue cracks occurring within the range of 15-45 mm from the specimen center, reaching 41.2% and 44.7%, respectively. The crack angle exhibited an increase corresponding to an increase in the content of 5-10 mm ceramsite, with the maximum average crack angle attaining a value of 86.5°. Conversely, a decrease in the content of 10-20 mm ceramsite resulted in a reduction in the crack angle. However, 20-30 mm ceramsite did not have a significant effect on the characteristics of fatigue cracks. The level of stress predominantly influenced the path of crack propagation. At stress levels of 0.55, 0.65, and 0.75, the highest proportions of crack angles fell within the range of 75° to 80°, with values of 47.1%, 43.8%, and 53.3%, respectively. Furthermore, an increase in stress levels did not affect the location of the cracks.