Fatigue Crack Propagation Analysis of Chemically Modified Crumb Rubber-Asphalt Mixtures

摘要

The fatigue fracture behavior of three asphalt mixtures is studied using semicircular specimen geometry.These mixtures consist of a control,a crumb rubber(CR)modified asphalt mixture,and a chemically modified crumb rubber(CMCR)-asphalt mixture.The mixtures are designed to meet the Superpave PG grade as close as possible,and the two rubber mixtures contain the same weight percent of crumb rubber.The number of fatigue cycles and the hysteresis loops are recorded at various intervals of crack lengths.Three specimens are tested from each material under tension-tension load control conditions at a frequency of 0.5 Hz.The maximum and minimum fatigue loads are kept constant for the three asphalt mixtures.It has been found that the chemical modification of the crumb rubber effects a pronounced improvement in the fatigue lifetime,the energy release rate,and the crack speed over the entire range of energy release rate of the asphalt mixture in comparison with the control and the crumb rubber mixtures.Scanning electron microscopy of the fatigue fracture surfaces(ahead of the initial crack tip)of the three mixtures is performed to identify the fracture features of each mixture.Ridges with increased intensity and frequency are associated with the second stage of the fatigue process of the CMCR mixture.These ridges are formed due to microstretching of the binder,and appear to be responsible for the superior fatigue fracture resistance of the CMCR-asphalt mixtures in comparison with the control and the CR mixtures.