Comparison of SBS and PP fibre asphalt modifications for rutting potential and life cycle costs of flexible pavements

Pakistan has a road network of approximately 250,000 km, which carries a significant proportion of passenger as well as freight traffic. Almost the whole length of this network is made up of flexible pavement, which uses asphalt concrete as the surface course. Asphalt pavements are subjected to many types of distresses, among which rutting is considered as an important issue. Rutting causes surface deformation and affects the frictional properties of the pavement surface because of accumulation of water in the wheel paths. Therefore, safe and sustainable operation of pavement can be ascertained by minimising such distresses through effective mix design and innovations in pavement materials. The presented study investigated and compared the performance of polymer-modified asphalt (PMA), polypropylene (PP)-fibre-modified and neat asphalt mixes, on their rutting behaviour and life cycle costs. It was found that PMA mixes performed better than the conventional and (PP) fibres-modified asphalt mix. Moreover, linear regression model developed in this study showed that the rutting behaviour of the asphalt mixes can be conveniently and effectively depicted through a linear model with pavement temperature and polymer type. The comparison of life cycle costs of these mixes showed that modified asphalt mixes of both types, although expensive in terms of initial cost, have a lower life cycle cost. Moreover, rut depths and life cycle cost of PMA were found to be lower than PP-modified asphalt samples. On the basis of this study, it is recommended that PMA binder should be used for constructing asphalt concrete pavements in Pakistan.