Improving the performance of heavy duty asphaltic concrete pavements.

This paper reports on a section of heavy duty pavement constructed in Victoria, Australia in 1991/1992 using an innovative approach to design and materials. The section is part of the SHRP organised Long Term Pavement Performance program. The two features of the design were the uses of HSMA (High Stiffness Modulus Asphalt) in the intermediate layers of the full depth asphalt pavement to increase stiffness and also the use of a binder rich fatigue layer at the bottom. Total thickness of the asphaltic layers was 230 mm. HSMA typically uses a large size mix (29 mm) and a bituminous binder with viscosity greater than 400 Pa.s at 60oC (penetration less than 50 units at 25oC). An estimated life improvement of 30% improvement of 30% results when the HSMA replaces conventional asphalt (top size of 20 mm) in the intermediate layer. Mix design of HSMA is done on gyratory compated specimens of 150 mm diameter. Compaction level simulative of heavy traffic loading is used. A testing system known as MATTA is proving very useful for characterising elastic and creep properties of asphaltic mixes. The equipment is similar in configuration to Nottingham Asphalt tester. Results of MATTA testing indicate that resilient modulus and dynamic creep are affected by compaction type used in preparing test samples. Stiffness results show HSMA to be about 50% stiffer than mix size 20 mm with conventional binder (penetration of about 55 units). Effect of binder content, temperature and loading time on HSMA are given.