| dc.description.abstract | In Uganda, a significant amount of investment is directed towards the construction of Asphalt pavement roads. Frequent failures such as rutting, fatigue and thermal cracking are attributed to many causes such as increase in traffic volumes, poor mix designs, poor drainage to mention but a few. To accommodate the ever increasing traffic load in varying climatic environments and to resist to such failures, major emphasis has been put on improving the performance of asphalt mixtures.
This approach has led to a fundamental variation in the design of long lasting asphalt pavements. To improve on the bitumen characteristics, specific performance enhancers have been investigated. These include additive modification, chemical reaction modification and polymer modification with styrene butadiene rubber (SBR), polyethylene, ethylene vinyl acetate (EVA), and styrene-butadiene-styrene (SBS).
In this research, styrene butadiene styrene and ethylene vinyl acetate have been used as modifiers to improve the rheological properties of bitumen and thus obtain better mixes.
Two aggregates were used: limestone and granite and two bitumen penetration grades, 60/70 and 80/100.
EVA and SBS were melted in an oven and added to both bitumen types in percentages of 3-7% and 2-6% respectively. The rheological properties of softening point (ASTM 36-70) and penetration at 25℃ tests (ASTM D5-86) were carried out accordingly. The result showed that SBS content for modification of 60/70 and 80/100 bitumen grades were determined at 2.8% and 3.8% respectively and EVA content of modification of 60/70 and 80/100 bitumen grades was 3.8% and 5% respectively.
Marshall mix design was used to obtain the Optimum Bitumen Content (OBC) for the control mixes in which for granite the OBC was 5.01 and 5.05 and Limestone was 5.20 and 5.38 for 60/70 and 80/100 bitumen grades.
Marshall properties of bulk density, stability, flow and voids in the mix for the modified mixes in which SBS and EVA were added were analyzed. It was found that SBS and EVA had improved these properties. The optimum SBS for granite were 2.9% and 3.4% and limestone 3.4% and 3.7% for 60/70 and 80/100 respectively. The optimum EVA for granite were 4.5 and 4.7 % and limestone 5% and 4.7% for 60/70 and 80/100 respectively. | en_US |
