POLYMERIC ADDITIVES AND THEIR ROLE IN ASPHALTIC PAVEMENTS .1. EFFECT OF ADDITIVE TYPE ON THE FRACTURE AND FATIGUE BEHAVIOR

The effect of polymer modifier type on the fracture and fatigue behavior of AC-5 asphalt mixture was studied. Three polymer modifiers which belong to the general group of thermoplastic polymers; styrene-butadiene-styrene block copolymer (Kraton), ethylene vinyl acetate (Elvax) and polyethylene (Novophalt) were considered. Beams were prepared from AC-5 asphalt binder containing 6% of each polymer modifier by weight and the same gradation. Flexural static tests were performed to evaluate the three polymer modifiers in comparison with unmodified AC-5 asphalt mixture. It was found that in general all three polymers increase the strength and the modulus of the asphalt pavement. SBS (Kraton) exhibits the highest flexibility and strength at room temperature (70-degrees-F). Invoking the modified crack layer model, fatigue crack propagation analysis revealed the superiority of the Kraton modified asphalt mixture to both Elvax and Novophalt mixtures. The modified crack layer model analysis of asphaltic pavements yields important information since it accounts for a combined comparison on the basis of crack speed, measured energy release rate, and the change in work expended on damage formation and history dependent viscous dissipative processes.