Yuki NAKAMURA
Development of a SMA mixture improving cracking resistance for thin overlay
Osamu TAKAHASHI
From the viewpoint of cost and environmental load reduction, pavement rehabilitation using thin overlay has been attracted attention in recent years. However, overlaying thin layer on cracked surface can easily lead reflective cracking. Therefore, development of an asphalt mixture having sufficient cracking resistance for thin overlay has been required.
Various methods for crack prevention have been studied in an improving HMA. Increasing flexibility of an asphalt mixture using a special modified material is one of remarkable methods. This study focused on the special modified material and discussed development of a HMA mixture having sufficient cracking resistance for thin overlay. Various physical tests were carried out to evaluate cracking resistance.
The special modified material consists of two elements, namely a low temperature brittleness modifier for reducing viscosity strength (A-agent) and a thermal expansion fine for imparting elasticity (B-powder). This study used a stone mastic asphalt (SMA) mixture which is excellent in rutting resistance and added the two specific modifiers into modified asphalt binder.
After determining a base blend of aggregate, modified binder content was selected by conducting indirect tensile tests. Static bending tests and fatigue tests were carried out to assess cracking resistance of the blend. The evaluation tests resulted that adding A-agent improved fatigue cracking resistance, and adding both A-agent and-B powder could further improve cracking resistance.
Wheel tracking test was also conducted in order to confirm rutting susceptibility. As the result, it was confirmed that adding the special modified material didn”Ēt introduce reduction of rutting resistance.
Results of Cantabro test showed that adding A-agent improved aggregate stripping resistance but adding B-powder still more decreased that. Therefore, mechanism and improvement for reduction of stripping resistance by adding B-powder should be studied in future.
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