Enhancement of porous asphalt mixture for resisting environmental conditions using modified asphalt

Open-graded-friction-course (OGFC) is a hot asphalt mixture usually utilized as a private purpose wearing course, because of open graded asphalt mixture and aggregates skeleton (stone-on-stone) contact, it contains a relatively high air voids percent, after compaction which are permeable to water. In this research one sort of gradation was used (9.5 mm) NMAS for preparing the OGFC asphalt mixtures, penetration grade 40/50, crushed aggregate, asphalt content prepared with 4 % and up to 6 % by weight of mixture with 0.5 % increments. Optimum asphalt content (OAC) was selected based on these criteria: air voids content, asphalt draindown, permeability, and abrasion resistance (aged and un-aged) condition. The mix performance had been investigated by indirect tensile strength and moisture sensitivity measured according to the (AASHTO T283-14). Results illustrate that the increasing of asphalt binder content leads to decrease in the air voids content, abrasion loss and permeability values, while with draindown increase, conversely, the indirect tensile strength test (ITS) had been meaningfully increased for both conditions and this is a perfect signal of resistance against humidity susceptibility. It can be resolved that the increasing of asphalt binder % in OGFC asphalt mixture, leads to increase the thickness of asphalt binder covering around the aggregates. On the other hand the outcome indicated that the addition of 4 % styrene-butadiene-styrene (SBS) to asphalt mixture gradation equaled to "9.5 mm NMAS" tends to improve the mix properties and exhibit higher TSR by (18.5, 16.4 and 13.7) % increases, as compared with original asphalt; at asphalt content (5.1, 5.6 and 6.1) %, respectively. Based on the above evaluation, the use of SBS gives the asphalt mixture better volumetric and performance properties which improved the adhesion between aggregate and asphalt that leads to reduced stripping of HMA, horizontal deformation, and increased the tensile stiffness modulus value.