Effectiveness of Waste Polymer Modified Bituminous Mixes in Pakistan

Abstract

Road network in Pakistan has been deteriorating steadily for the past couple of decades. Some of the major factors attributing to this decline are increase in road traffic, improper construction and maintenance practices and lack of maintenance funds. To alleviate this process, several measures may be effective, such as, improved traffic management, securing additional funds for timely maintenance, improved and innovative roadway design, use of better quality of materials and the use of cost-effective construction methods. One of the innovative methods being used around the world for improving road networks is use of polymer in asphalt mix as a modifier. With this perspective, this research project aimed at exploring the potential prospects of crumb rubber i.e. waste tyres to enhance asphalt mix properties as a polymer. Objectives of this project also included determining the best method of adding the crumb rubber to the asphalt mix and comparing the effectiveness and performance of conventional asphalt mix and asphalt mix modified by crumb rubber, high density polyethylene (HDPE) i.e., waste plastic bottles and low density polyethylene (LDPE) i.e., waste plastic bags. The polymer was shredded to powder form and then used in preparing polymer modified asphalt mix. Crumb rubber was added to coat the aggregate (dry process) whereas adding crumb rubber to the bitumen (wet process) did yield revealing results. Marshall Mix design was used, first to determine the optimum binder content and then further to test the modified mixture properties. In total 58 samples were prepared of which 15 samples were used to determine the optimum asphalt binder content and the remaining samples were used to investigate the effect of modifying the conventional asphalt mix with crumb rubber (C R). The optimum asphalt content was found out to be 4.5%. Eight proportions of powdered crumb rubber by weight of the optimum binder content were selected to be tested (i.e. 4, 6, 8, 10, 12, 14 and 16%). The tests include the determination of bulk density, stability and flow. The optimum proportion of the modifier is found to be 10% by the weight of bitumen content. All the results of this study were compared to that of previous studies which explored the prospects of adding HDPE and LDPE in the asphalt mix. Rutting is the major cause of road failure in Pakistan due to violation of axle load limits, improper design practices and exposure to high tire pressure and high temperatures. Rutting test was performed to measure the relative rutting resistance of controlled samples and crumb rubber