Open-graded AC

The use of open-graded AC for binder and base course is not as popular as dense-graded AC mixtures and, when used, its use is limited to surface course. 

The European practice for surface course layer is to use BBTM and, when circumstances arise, such as ultimate reduction of traffic noise generated or maximising spray reduction, to use PA. If open-graded AC needs to be designed, CEN EN 13108-1 (2008) is used since it covers all types of AC mixtures. 

With regard to the American practice for designing open-graded mixtures, ASTM D 7064 (2008) is used. These mixtures are recommended to be used in friction (surface) courses. Since these mixtures are similar to PA, they are described in detail in Section 5.6.2. 

---