Validation of the Superpave[TM] asphalt binder fatigue cracking parameter using an Accelerated...

An Accelerated Loading Facility (ALF) was used to validate the Superpave asphalt binder parameter for fatigue cracking, G*sin(delta). The ALF is a full-scale machine for pavement testing that applies one-half of a single, rear truck axle load. The speed of the ALF and the applied load were constant

Two unmodified asphalt binders were used. These hinders had Superpave performance grades of 58-34 and 64-22 and continuous intermediate-temperature performance grades of 9 and 17, respectively. Both asphalt binders were from the same crude source. A single aggregate gradation and a single asphalt hinder content were used. Two layer thicknesses of asphalt pavement were tested: 100 and 200 millimeters (4 and 8 inches). Each pavement was tested at three temperatures: 28, 19, and 10 degrees Celsius (82, 66, and 50 degrees Fahrenheit). A total of 12 pavement sites (two binders at two thicknesses and three temperatures) were tested.

The pavements failed sooner at the middle test temperature of 19 [degrees]C (66 [degrees]F) for a given asphalt binder and pavement layer thickness. Neither the strain-control parameter, G*sin(delta), nor the stress-control parameter, G*/sin(delta), alone can explain the effect of temperature. As expected, each 100-mm (4-inch)-thick pavement failed sooner than the 200-mm (8-inch)-thick pavement layer with the same asphalt binder mad pavement test temperature.

Only one of the six comparisons used to evaluate the effect of binder grade on fatigue-cracking performance showed that the mode of loading was strain control, which is the mode of loading used by the Superpave asphalt binder specification. Four of six comparisons indicated that the mode of loading was stress control, although the stress-control parameter, G*/sin(delta), could not explain the effect of test temperature on fatigue-cracking performance. The sixth comparison was inconclusive with regard to the applicable mode of loading.

The pavement data indicated that the mode of loading can change with temperature. For the 100-ram (4-inch)-thick pavements, the mode changed from strain to stress control with a change in temperature from 28 to 19 [degrees]C (82 to 66 [degrees]F). Fatigue cracks in all pavements started at the bottom of the asphalt pavement layer.