Evaluation of rubber modified porous asphalt mixtures

A porous pavement is a type of sustainable pavement that allows stormwater to infiltrate through the pavement into the natural soil bed. Rubber modified binder is the combination of regular asphalt binder mixed with ground crumb rubber, which is derived from used rubber tires by shredding or grinding the tires into small fragments. This research investigated the effects of rubber modified binder on the performance properties of porous asphalt mixtures, which include draindown, porosity, permeability, abrasion resistance, moisture susceptibility, and rutting resistance.;The addition of cellulose fibers has been used to increase the optimum binder content of porous asphalt mix designs without increasing the binder draindown. The increased optimum binder content (OBC) allows the asphalt binder to create a thicker coating (or stronger bond) between the aggregate particles, creating a more durable and stronger structure. This research focused on replacing the cellulose fibers with rubber modified binder in an effort to increase the OBC of mix designs without increasing the binder draindown.;This study found that the use of the rubber modified binder resulted in an increase in binder viscosity at 135°C and 165°C when compared to the PG 64-22 base binder. The 12% ground tire rubber (GTR) increased the performance grade of base binder to a PG 76-22. Both the 5% GTR and the 12% GTR increased the failure temperature of the binder.;This study also found that the use of the rubber modified binder was effective in minimizing the effect of binder draindown and was comparable to the addition of 0.3% cellulose fibers to the mix. The rubber modified binder was effective in minimizing the effects of long-term draindown as indicated by the similarities in the permeability of the mixtures after 28 days of long-term aging at 60°C compared to the permeability before aging.;The results of the study indicated that the use of rubber modified binder or fibers reduced the abrasion loss: thus, generally increasing the durability of the mixes. The addition of the cellulose fibers and GTR reduced the moisture susceptibility of the mix designs as evidenced by TSR values greater than 90%. Finally, it was found that the addition of the rubber modified binder increased the rut resistance when compared to PG 64-22 without cellulose fibers but decreased the rut resistance when comparing it to mixes with cellulose fibers and SBS modified binder.