ASPHALT MIX DESIGN COMPARING PROPERTIES OF BITUMINOUS CONCRETE MIXES USING MORTH AND SUPERPAVE GRADATIONS FOR HEAVILY TRAFFIC LOADS

Abstract

Asphalt paving mixes designed by the marshal mix method  have been failing prematurely on our roads. One of the reasons for such failure is inadequate initial compaction. Densities achieved under 75- blow Marshall compaction in the laboratory do  not simulate the field densities of the mix after it has undergone secondary compaction due to traffic. When the air voids in the mix decrease to below 3 percent during such densification and as the viscosity of asphalt in the mix decreases sharply in summer, the mix permanently deforms as a rut under the wheel loads. Three factors contribute to good performance of an asphalt mix carrying heavy axle loads in hot climates. They are adequate initial compaction so that secondary compaction under traffic is minimized, sufficient asphalt content for durability of the mix and enough air voids in the mix for its stability. all the three factors are influenced by the VMA of the mix. A high aggregate shape and surface texture influence the VMA to same but it is largely influenced by the aggregate grading dense grading give rise to low VMAS and open grading to high VMAs. This research suggests a modification to the marshal design procedure for the design of asphalt mixes.  Thee modification involves adjusting the aggregates grading to achieve higher VMA values for creating more space to incorporate higher asphalt contents and checking the mixes for „refusal density‟ for ensuring its stability under secondary compaction due to traffic . So, to solve the problems due to heavy traffic loads and the Environmental effects , atmospheric effects such as seasonable effects on pavement(asphalt) we are investigating using Super pave technology testes in laboratory to solve this issues. Superpave and Marshall mix designs using local aggregates were done to study the suitability of the Superpave mix design as compared with the Marshall mix design for low-volume roads, especially shoulders... Mix samples were compacted in the Superpave gyratory compactor with the applicable number of gyrations and were compacted with the Marshall hammer by using 200 blows per face.