Performance Improvement of Porous Asphalt Mixtures using Crumb Rubber and Steel Slag Powder

In recent decades, porous asphalt has been extended for surface drainage in various regions throughout the world. The permeability of porous asphalt has an important role in the performance of asphalt pavements in the rainy weather. The most remarkable problem related to the porous asphalt is its short service time. Considerable efforts have been made to enhance the mechanical properties of porous asphalt. Steel slag produced from manufacturing processes is a by-product commonly deposited in landfills and thus results in many serious environmental problems. Very high amounts of steel slag is produced in Iran and if these waste materials could be well put into practical uses, it would decrease the burden on the environment. This paper presents a series of tests on modified bitumen and porous asphalt with steel slag powder (SSP) and crumb rubber (CR). Reference tests were also conducted on control bitumen and porous asphalt. The material properties for different types of bitumen and porous asphalt were evaluated by penetration degree, softening point, ductility, Marshall stability, indirect tensile strength (ITS), porosity, and permeability. The results of current research demonstrated that it was feasible to replace partial CR with SSP. SSP can not only increase the softening point and ductility, but also reduce the penetration degree. Compared with the control porous asphalt, the modified porous asphalt with SSP/CR had higher Marshall stability, Marshall quotient (MQ), ITS and porosity. When 90% of CR was replaced by SSP in porous asphalt, highest permeability was observed. From these results, it was concluded that SSP can potentially be used as modifier replacement in the production of modified porous asphalt.