Evaluation of Thick-Lift Paving of Asphalt Concrete

Abstract

This research paper focuses on the feasibility of thick-lift paving with asphalt concrete. Thick-lift paving is the placement of asphalt concrete in a lift greater than the allowable maximum by an agency, often four to five times the nominal maximum aggregate size. Thick-lift paving offers potential benefits including streamlining operations and eliminating the bond interface in multi-lift layers. However, it also presents challenges such as potential for inadequate compaction and lower ride quality. Asphalt concrete design and construction specifications from 19 state Departments of Transportation were reviewed. In the field, 28 thick-paving test sections were constructed with different lift thicknesses (3 to 10 in.), two mix designs, different paving screed settings, and different rolling patterns. All pavers were equipped with tamper bar screeds. During construction, the researchers monitored asphalt cooldown time and mat density. After construction, the ride quality of each section was measured, and cores were tested for air voids content. Acceptable mat compaction was achieved in all test sections, with additional roller passes having the most significant effect on compaction. The study also found that thick one-lift layers yielded better and more uniform compaction than two-lift layers. Thicker lifts had significantly longer cool down times and potentially increased roughness. Recommendations included the possible use of tamper bar screeds and additional roller passes to improve compaction. Scenarios that are suitable for thick-lift paving were identified.