Effect of Aggregate Gradation on Rutting of Thin Asphalt Overlay

Permanent deformation (rutting) of asphalt pavements has a major impact on the service life of pavements. Rutting reduces the performance of the pavement and produces serious hazards for highway users. Due to the axle loads incensement, and high local summer temperature, rutting became the major distress in flexible pavements for many countries. Recently, thin asphalt overlay (TAO) is recommended as a significant remedy technique for deteriorated pavements. Aggregates are one of the main structure materials asphalt paving mixtures, whereas, aggregate properties remarkably effected on the asphalt pavements performance. Aggregate gradation is representing the significant feature of aggregates that affecting permanent deformation of traditional hot mix asphalt (HMA) thick pavement layers. The aim of this study is to examine the influence of aggregate gradation differences on rutting features of modified TAO mixtures that comprising waste polymers. The evaluation process included the preparation of polymer modified asphalt (PMA) comprising two types of additives, namely, Crumb Rubber Modifier (CRM) and Low-Density Polyethylene (LDPE). CRM and LDPE in the form of fines that have a particle size under 250 um were used as additives to liquid neat asphalt, individually and collectively by weight of virgin asphalt; i.e., PMA included 15.0% of CRM and (2.5. %, 5.0%, 7.5% and 10.0% of LDPE. Three types of aggregate gradations were used, i.e. 12.5, 9.5 and 4.75mm, Nominal maximum aggregate size, (NMAS). The Superpave mix design system was adopted in volumetric proportioning of prepared mixtures, while Wheel Tracking (WT) test was used to determine the rut depth characteristics for prepared mixtures. about 30 asphalt concrete specimens were prepared to forecast the TAO behavior concerning permanent deformation for wearing course type III A and B according to State Corporation of Roads and Bridges in Iraq, while for 4.75mm, NMAS (sand asphalt layer) an abroad specification was used. Results demonstrated that the aggregate gradation plays a vital role in increasing permanent deformation for several type of TAO mixtures. Also, the addition of CRM by 15% to the neat asphalt led to an increase in the resistance of the mixture to permanent deformation. Moreover, PMA with LDPE became hardener (higher viscosity) which led to increase binder stiffness, whereas a consequent is stiffening the mixture. Therefore, optimizing aggregate gradation with PMA including waste polymers can limited the rutting occurrence distinguishably