In recent years, modified asphalt mixtures have become increasing in the construction of flexible pavements. Several classes of modified binders have been used in asphalt pavements. The main modifiers are fillers, fiber, rubber, and polymers. Because conventional asphalt mixtures can not resist high stress due to the fact that the axle loads and tire pressures are continuously increasing, attention have been increasing towards the use of polymers modified asphalt.
The main purpose of this investigation is to evaluate the effect of adding the polypropylene pellets on the 80/100 and 60/70 asphalt cements. To achieve the objective of this investigation, the different properties of modified and unmodified asphalt cements such as penetration, softening point, kinematic viscosity, absolute viscosity, specific gravity, durability and penetration index were investigated.
The variables considered in this study are two different grades of Alexandria asphalt cement (80/100 and 60/70 pen.) and the polypropylene ratio by weight of 80/100 asphalt cement at 1,2,3,4,6 and 8%, and also 2 and 4% by weight of 60/70 asphalt cement.
The results of this study indicate that the addition of polypropylene to Alex. asphalt cement and its asphalt mixtures at all ratios improved the all properties. Adding 3, 2 and 1% polypropylene to 80/100 asphalt cement by weight alters its penetration, kinematic viscosity and softening point respectively to be 60/70 asphalt cement. The addition of 6% by weight of Alex. 80/100 asphalt cement alters its penetration to be 40/50 asphalt cement and also the addition of 3% alters its kinematic viscosity and softening point to be 40/50 asphalt cement. The addition of polypropylene up to 4% by weight of Alex. asphalt cement improves its thermal characteristics by increasing its penetration index, above this percent the improvement decreases thus, the optimum additives percent can be taken as 4% by weight of Alex. asphalt cement.
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