Kota TAKANO

Estimation of Stress Relaxation Characteristics of HMA Based on Evaluation of Binder Properties

Osamu TAKAHASHI    Takeshi NAKAMURA

 HMA (Hot-mix asphalt concrete) has viscoelastic behavior and stress relaxation characteristics. This is a property that is imparted by using a viscoelastic asphalt as a binder. Therefore, the stress relaxation property of HMA is dominated by the influence of the binder properties. It has been reported that increasing the polymer content of the binder can suppress the occurrence of plastic flow and top-down cracks of HMA. On the other hand, it is known from the ERT (Elastic Recovery Test) using a load measuring type elongation tester that when the polymer content is increased, the elastic recovery rate increases and stress relaxation becomes difficult.
 Thence, the change of the physical properties of HMA with the change of the properties of the binder was investigated, and aimed to indirectly evaluate the change of the stress relaxation characteristic of the HMA using the result of the binder property evaluation test.
 In comparing the property evaluation test of the binder and the physical property evaluation test of the HMA, ERT and uniaxial compressive stress relaxation test were carried out and examined by focusing on the stress relaxation time. 
 From this result, a certain correlation was found between the stress relaxation time of ERT and the stress relaxation time of HMA. Regarding this, it was found that the stress relaxation time of binder obtained from ERT shows the stress relaxation time of HMA when the maximum stress decreases to about 30%. It was found that the optimum maximum stress ratio varies with the grain size of aggregate.
 From the above, it was concluded that the change in the stress relaxation characteristic of the HMA can be indirectly evaluated based on the binder property evaluation.