Jun YOKOI

Study on the correlation between crack opening angle and crack propagation of asphalt concrete by semicircular beding test

Osamu TAKAHASHICTakeshi NAKAMURA

In Japan, four-point bending fatigue test is being conducted as one of the tests to evaluate fatigue fracture resistance of asphalt concrete. However, this test has complicated equipment setting and testing time ranges from several hours to one day per test specimen from start to finish. So, this test lacks simplicity. On the other hand, in Europe and the USA, tests called SCB (Semi Circular Bending) test is standardized and it is carried out on metals and soil as a test to investigate destructive energy and so on. In this test, physical properties are evaluated by applying a load to a semicircular specimen and destroying it. The time required is about 2 minutes for each specimen.    So it is simple. Therefore, focusing on the progress of cracks that can be confirmed by the SCB test like the four-point bending fatigue test too, through this test, whether the fatigue fracture resistance of asphalt concrete was more easily evaluated.
Calculated break strength, breaking energy, flexibility index as parameters of ductile fracture, crack opening angle, crack tip opening displacement, crack tip opening angle as parameters of brittle fracture from the results obtained by conducting the SCB test in this study. Then, the correlation between these parameters and the rate of crack propagation speed calculated from the result of four-point bending fatigue test was examined, and the following knowledge was obtained. 
The flexibility index was the most correlated, and the coefficient of determination was 0.907. And the crack tip opening angle correlates well with the crack propagation speed at 10 Ž. 
From the above, the flexibility index by the SCB test has a high correlation with the crack propagation speed by the four-point bending fatigue test and there is a possibility of utilization as a parameter to evaluate fatigue fracture resistance instead of four-point bending fatigue test. In addition, when fatigue fracture resistance was evaluated by using the crack tip end opening angle, it was found that availability is improved if the test temperature is 10 Ž.