Name Ryuhei KOBAYASHI
Title Evaluation of Crack Resistance for Asphalt Mixtures by Step-By-Step Direct Tensile Tests
Asvisor Osamu TAKAHASHI
One of fatal failure forms for asphalt concretes (AC) is cracking. Cracking resistance of AC is usually evaluated by a bending test or a direct tensile test with a constant stain rate. However, stress relaxation of the AC in fields obviously affects performance of cracking resistance, since field deforming actions, casing fatigue cracking, thermal cracking, or reflective cracking, alternate between tension and compression with rest periods. It is generally known that the relaxation property of the AC is comparably serious. Some grades of straight asphalt (SA) and various kinds of modified asphalt (MA) are widely used as a binder of AC in Japan. It means that relaxation properties of AC for wearing course have wide variety, and cracking resistance of the AC should be assessed with taking their relaxation properties into account.
This study evaluated cracking resistance of AC mixed with a SA and various MAs by carrying out two different types of direct tensile tests. One was a conventional direct tensile test with a constant strain rate. The other was a step-by-step direct tensile test, which had strain holding periods in a process of stretching with a constant strain rate. Influence of stress relaxation on the cracking resistance was investigated by comparing both results of strain at failure on each the tensile test. The objective of the study was to evaluate cracking resistance of the AC with focusing the difference of stress relaxation properties.
The results showed that a strain at failure measured by the step-by-step direct tensile test was higher than that by the conventional direct tensile test. The degree of difference depended on viscosity of the binders and adhesion area of aggregate particles. Strain at failure is high, but stress relaxation is low on the AC using a high viscous MA.
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