Analysis on fatigue crack growth laws for crumb rubber modified (CRM) asphalt mixture

In recent years, crumb rubber has been applied widely in asphalt pavement, and many researchers have indicated that crumb rubber modified (CRM) asphalt mixture is an environmentally friendly material. In this study, the notched semi-circular bending (SCB) test was employed to study the fatigue cracking property for CRM asphalt mixture. Then the cracking growth length was obtained by image processing technology, and its correlation with the fatigue number was established and studied in this paper. Concurrently, the influence of gradation type, asphalt content, test temperature, stress ratio, loading frequency, rubber powder concentration and rubber powder size on CRM asphalt mixtures’ fatigue life and crack growth laws were investigated by this method. The results indicated that the gap-graded CRM asphalt mixture had a longer fatigue life and a lower crack growth rate than the continuous graded mixtures Moreover, at the optimum asphalt content, the fatigue life was much longer and the crack growth rate was much lower at smaller loading times with higher loading frequency at the CRM asphalt mixture concentration of 20% using the smaller 80 mesh fine crumb rubber size.