Crack Initiation Model from Asphalt Slab Tests

The Strategic Highway Research Program (SHRP) fatigue crack initiation life prediction model was based on a sophisticated analysis of the results of intensive bending beam fatigue tests under controlled stress and controlled strain. The definition of crack initiation was defined as the period during which initial microcracks developed into a macrocrack 7.5-mm deep. Due to the lack of the measured crack data, the numbers of loading cycles corresponding to the 7.5-mm deep crack were not observed from the tests but predicted based on a microfracture mechanics model. The objective of this study was to evaluate SHRP fatigue crack initiation life prediction model with the crack measurements in laboratory slab fatigue tests. The study showed that the SHRP crack initiation life model significantly underestimated the fatigue crack initiation life for the slabs. However, the ratio of the observed fatigue life from the slab tests to the crack initiation life predicted from SHRP equation was shown to be approximately constant.