Evaluation of fatigue (alligator) cracking in the LTPP SPS-6 experiment

The performance of Crack, Seat, and Overlay (CS&O) pavement sections is evaluated in terms of fatigue cracking (also known as alligator cracks). Data extracted from the Long Term Pavement Performance (LTPP) SPS-6 experiment were divided into two categories based on weather region, namely Wet-with-Freez (WF) and Wet-with-No-Freeze (WNF). These data were then analyzed and regression models were developed. Data for pavement sections in California were evaluated separately leading to the development of a third regression model. In the WF region, thicker overlays did not appear help to minimize alligator cracks in sections with unbound bases. Sections with bound bases outperformed those with unbound bases in the WF region. Increasing the leveling course thickness from about 30.5 to 63.5mm helped to reduce alligator cracks in the California sections. Regression analyses suggest that sections in the WNF region will outperform their counterparts in the WF region and in California up to an age of approximately 12 years. The California sections are expected to exhibit approximately 56 percent alligator cracks after 10 years of service.