Improving cohesiveness of porous friction course asphalt mixtures

Abstract

The use of porous friction course (PFC) provides numerous safety benefits and improves the noise quality of surrounding areas. Many agencies once used PFC for these reasons, but have since stopped using PFC due to performance issues. PFC pavements have reportedly been prone to ravelling and cracking, which leads to reduced service life. In addition, PFC is also typically more expensive than a dense-graded mix due to its use of high-quality aggregates, modified asphalt binder, and higher asphalt binder contents. Research is needed to extend the service life of PFC pavements in order to encourage agencies to start, or continue, use of PFC for its safety benefits. The objective of this research is to address the ravelling and cracking distresses commonly seen by adjusting the asphalt and dust content of PFC mixes to improve durability. This was accomplished by using an array of performance tests to evaluate the effect of additional fine aggregate passing the 0.075 mm (P_−0.075) sieve on two PFC mixtures: one that had good field performance (up to 18 years) and one that had poor field performance (less than 8 years). It was found that the Cantabro test was a good indicator of mix performance and a maximum loss of 20% is recommended. The study revealed the importance of increased percent passing the 0.075 mm sieve to provide more durable PFC mix designs. An increased P_−0.075 content had a positive effect on almost all of the results; thus, it is recommended that the current P_−0.075 gradation band be expanded.

Keywords:

• porous friction course
• Cantabro loss
• durability
• safety
• ravelling