Comparative Analysis of Low and High Density Polyethylene 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 is 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 waste high density polyethylene (HDPE) i.e. waste plastic bottles to enhance asphalt mix properties as a polymer. Objectives of this project also included determining the best method of adding the HDPE to the asphalt mix and comparing the effectiveness and performance of HDPE and low density polyethylene (LDPE) modified asphalt mix with that of conventional asphalt mix. The polymer was shredded to powder form and then used in preparing polymer modified asphalt mix. HDPE was added to coat the aggregate (dry process) whereas adding HDPE to the bitumen (wet process) could not be materialized as the polymer and bitumen could not form a homogeneous mix. Marshall Mix design was used, first to determine the optimum bitumen binder content and then further to test the modified mixture properties. In total 57 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 high density polyethylene (HDPE). The optimum asphalt content was found out to be 5%. Six proportions of polyethylene by weight of the optimum binder content were selected to be tested (i.e. 4, 6, 8, 10, 12, and 14%). The tests include the determination of bulk density, stability and flow. The optimum proportion of the modifier is found to be 8% by the weight of bitumen content. All the results of this study were compared to that of a previous NUST/MCE study which explored the prospects of adding LDPE in the asphalt mix.