Syota ISHII

Evaluation of Rutting Resistance of Asphalt Concrete by Stress Relaxation Behavior of Binder

Osamu TAKAHASHI, Takeshi NAKAMURA

Since Asphalt Concrete uses viscoelastic asphalt, this material exhibits a viscoelastic behavior as well as stress relaxation properties. Therefore, the physical properties of asphalt concrete are influenced by the characteristics of the binder itself.
In past studies, binder properties were evaluated by means of a measuring tester of force ductility test, which also provides insight into the physical properties of asphalt concrete. As a result, regardless of the type of binder and the aging degree, the resistance to deformation, cracking resistance and resistance to fatigue failure of asphalt concrete were evaluated from the binder properties. However, since only the cracking resistance and fatigue failure behavior were evaluated, knowledge on the plastic rutting resistance of asphalt concrete could not be obtained from this type of test. 
 Therefore, the aim of this study is to explain the relationship between the stress relaxation behavior of binder and the plastic rutting resistance of asphalt concrete. The proposal of a method that can be used to test the elongation properties of asphalt binder, and providing insight into a method that can properly assess the properties of old binder are also part of the main purpose of this study.
 When polymers are blended with asphalt binder, plastic rutting resistance and fatigue failure resistance of asphalt concrete are known to improve. However, the elastic recovery rate of the asphalt binder becomes higher, and binders go through stress relaxation with difficulty. The results of evaluating the stress relaxation properties of the binder using a measuring tester of force ductility test indicate that the stress relaxation time became longer, while dynamic stability increased with the addition of polymers and aging of this additive.
 In addition, properties of aged-modified asphalt binder were compared using mixtures containing regenerating additive and a new asphalt binder. Results indicate that even if the DR value, which represents the deformation resistance of asphalt concrete, is about the same, cracking resistance and stress relaxation properties do not decrease so much. Therefore, the old binder having a high FD value, which indicates fatigue failure resistance of asphalt concrete, and long stress relaxation times, can maintain the desired properties of asphalt binder by using regenerating additives.
 With this experimental work, various properties of asphalt concrete can be indirectly evaluated from the binder properties, and a test method using a measuring tester of force ductility test was also proposed. In addition to this result, a method that can be used to enhance and recover the desired properties of old asphalt binder was also proposed in this study.