The effect of lift thickness on permeability and the time available for compaction of hot mix asphalt pavement under tropical climate condition

This study investigates the effect of lift thickness on (i) permeability and (ii) the time available for compaction (TAC) of hot-mix asphalt (HMA) mixes under tropical climate condition. A total of 14 HMA mixes consisting of various types, gradations, and nominal maximum aggregate sizes (NMAS) were selected. The heights for thickness (t) to NMAS ratios of 2.0, 3.0, and 4.0 were determined with appropriate mass to produce 7.0 ± 1.0% air voids. The bulk specific gravity of the samples was determined using the vacuum sealing method. The laboratory permeability test and the relationships between permeability and lift thickness were evaluated. To achieve the second objective, seven field test sections with different HMA mixes were constructed; each was about 40 m long and 3.5 m wide. Each test section was paved with thickness (t) to a nominal maximum aggregate size (NMAS) ratio of 2.0 at the beginning of the section and gradually increased to a t/NMAS ratio of 5.0 at the end of the section with air temperatures during construction ranging from 26 to 35 °C. It was found that HMA mixes with a lift thickness of 30 mm and less with coarse gradation have a greater chance of having a permeability problem, even though they are compacted at the right density. In addition, the thinner the mix layer, the faster the mix cools, thus reducing the TAC. The results also suggest that the TAC for a 25 mm lift is 13 min, 23 min for 32 mm, 32 min for 38 mm, and is expected to be more than 50 min for 44 mm and above.