Evaluation of Cellulose Based Stone Mastic Asphalt on a Test Section in Pakistan

Abstract

After decades of experience in road construction, the highway experts have concluded that the major failures on our road network are rutting and fatigue cracking. These failures are due to the high temperatures and the prevalent overloading. In order to encounter these defects we have to resort to other trends by moving from the conventional dense graded asphalt mixtures and adopting new technologies. The answer to our problems is Stone Mastic Asphalt (SMA). SMA originated in Germany in the late 60s in response to the studded tyres. SMA, which is a gap graded mixture, provided durable pavements which exhibited high resistance to rutting by heavy truck traffic and proved to be extremely effective in combating wear. In order to evaluate the characteristics of Cellulose based Stone Mastic Asphalt we entered into a collaboration with National Highway authority to lay a test-section on in-service road on National highway N-5. The old pavement was evaluated using destructive and non-destructive testing. Rehabilitation design was carried out for the existing pavement and an asphaltic base course was laid for reinforcing the pavement prior to the laying of SMA wearing course. Stone Mastic Asphalt mix design using cellulose fiber was carried out in collaboration with the German Experts. The aim was to find an optimum mix design which may suit to our local conditions. Different trial blends were made, the one satisfying the SMA Mix volumetrics was selected. The transportation, paving and rolling were done according to the specifications. The methodologies will be discussed in detail in the proceeding chapters. The test section was opened to traffic after a heal period of five days. The performance of SMA mixture two (02) months in-service now has been a success. With temperature regime ranging between 38oC to 45oC and heavy traffic plying no settlement in form of rutting or shear deformation has been observed. The use of SMA on this trial section has opened up new avenues of research in asphalt paving industry in Pakistan with regard to its characteristics i.e. high bitumen content and relatively fine SMA mix as laid. The use of cellulose fiber as a binder carrier has performed well to date since no fat spots or other defects associated with high binder contents are observed. Monitoring the test section in the ongoing summer seasons and forthcoming winter months will be interesting in terms of SMA behavio