Creep properties of additive modified asphaltic concrete under repeated loading

Since about three decades, because of constantly increasing traffic volumes,axle loads, tire pressures and often inadequate maintenance more failures than anticipated occur on highway flexible pavements. The most common failures on pavements are rutting, cracking, stripping and polishing on the surface. Rutting which occurs because of permanent deformation of bituminous hot mixes under repeated loading shortens the service life of flexible pavements. Therefore, creep behavior of bituminous mixes should be taken into consideration while designing a paving mixture. Likewise, in order to estimate the rut depth the relationship among the factors which affect the creep behavior should be well understood. To prevent or delay rutting and cracking the use of polymer modified bitumen or additives in hot mix asphalts (HMA) is constantly increasing. In this study, different additive contents were used in the same dense graded asphalt concrete to investigate the creep behavior of the mixture. For this purpose a standart wearing course mixture was chosen and UMATTA test equipment was employed. 30 Marshall specimens compacted with 75 blows were prepared. IS of them were used in stability and flow tests and the rest were used in repeated load creep test. In creep tests, Marshall specimens were tested at constant temperature (SO °C) and constant pressure (500 kPa). Specimens with different additive contents are tested under constant pressure with constant loading - rest times.(l sec.) Specimens had 0.4%, 0.5%, 0.6% and 0.7% additive contents by weight of aggregate. For each additive content 3 specimens were tested. One of the objectiveswas to compare the creep behavior of specimens with and without additive. Only one type of additive (poliolofine) was used. By the evaluation of the results, it was observed that the use of additive decreased the permanent strain by 25 % on average. However the use of the additive hasn't given significant results for the change of resilient modulus. By the evaluation of the results, it was observed that the use of additive increased the stability values by 20 % on average. Maximum stability values are to be seen at 0.6 % additive content.