Modelling and permanent deformation analysis of low-density polyethylene (PE)-modified bitumens and asphalts

The present investigation aimed at evaluating the permanent deformation responses of bitumens modified with low-density polyethylene - either with or without polyphosphoric acid (bitumen+PE and bitumen+PE+PPA) - and by considering bitumen tests (MSCR – multiple stress creep and recovery), rheological models and asphalt tests (FN – flow number). The formulations were graded as PG 76-xx and the standardised MSCR tests were conducted at 64, 70 and 76°C. The bitumen+PE+PPA showed a higher resistance to permanent deformation than the bitumen+PE according to MSCR and FN tests in a general context, even though none of the formulations may be assumed as overly stress sensitive (Superpave® parameter lower than 75% in all cases), neither they depicted high levels of elasticity due to their small per cent recoveries (all lower than 25%). It was also hypothesised that the contributions of PE and PPA on the increases in the stiffness of the bitumen+PE+PPA were made individually.