The purpose of this investigation is to evaluate the effect of adding the polypropylene pellets (PP) on the asphalt cements and their asphalt mixtures properties, and the long-term performance.
The variables considered are the effect of adding different ratios of PP on Alex 80/100 and 60/70 A.C properties. The added ratios are 1, 2, 3, 4, 6 and 8% by weight for 80/100 A.C & 2 and 4% by weight for 60/70 A.C. For asphalt mixtures, the variables considered are the effect of the above modified asphalt cements on Marshall properties and on rutting results as evaluated by wheel tracking machine at 25 and 60°C at 6.25 kg/cm2 stress level and on creep results at three stress levels of 4.2, 6.25 and 9.38 Kg/cm2 at 25°C.
The results of this study indicate that the addition of PP to Alex. A.C and its asphalt mixtures at all ratios improved the all properties. The addition of 3and 4%PP by weight of Alex. 80/100 asphalt cement alters its physical properties to be similar to 60/70 A.C. The addition of polypropylene up to 4% by weight of Alex. A.C improves its thermal characteristics by increasing its penetration index. Increasing the percentages of polypropylene increases stability and Marshall stiffness and decreases the flow of Alex. asphalt concrete mixtures but the unit weight, voids in mineral aggregates and optimum asphalt content are not sensitive. The 80/100 asphalt mixture at 4% PP/A ratio provides much better long-term performance than the others. Addition of PP to A.C results in shafting the rutting time from 0 to 35 and 45 minutes for 80/100 asphalt mixture at 3 and 4% PP at 25 ºC. Moreover the 80/100 asphalt mixture at 4% PP gives the lowest rate of increasing in creep when increasing the stress level. Finally, correlation between wheel tracking test and creep test is developed at 25°C and stress level of 6.25 Kg/cm2.