Evaluating of asphalt additives for improved cracking and rutting resistance of asphalt paving mixtures

A laboratory investigation was conducted to evaluate the effects of a few asphalt additives on the cracking and rutting resistance of asphalt paving mixtures that might be considered for use under Florida conditions. The five types of additives evaluated in this study include (1) gilsonite, (2) ground tire rubber (GTR), (3) styrene-butadiene rubber (SBR), (4) ethylene vinyl acetate (EVA) and (5) styrene ethylene butylene styrene (SEBS). These additives were blended with an AC-5, AC-10, AC-20 and AC-30. These modified and unmodified asphalts were subjected to the thin film oven test (TFOT) to simulate the short-term aging effect that occurs in the hot-mixing process, and followed by the California tilt oven (CTO) and SHRP pressure aging vessel (PAV) processes to simulate the additional aging of the asphalt binders in the field. All these asphalts and asphalt blends were evaluated by various rheological and chemical tests.; The five modified asphalt blends, and unmodified AC-20 and AC-30 were also used to make Florida type S-I structural course mixtures. These mixtures were compacted by the gyratory testing machine (GTM) at different compaction levels and aged according to the SHRP proposed long term oven aging (LTOA) procedure. These aged and unaged asphalt mixtures were evaluated by resilient modulus, indirect tensile strength and indirect tensile creep tests. Asphalt residues were recovered from the broken samples and evaluated by various rheological tests.; The test results indicate that the addition of the five types of modifiers is beneficial for the improvement of rutting resistance of the pavement. The addition of GTR and SBR is beneficial to the cracking resistance of asphalt pavement materials at low temperatures. The SBR modified asphalt mixtures show better rut resistance as compared with those of GTR and SEBS modified mixtures. The GTR and SBR modified asphalt mixtures have lower resilient modulus than that of the unmodified mixtures at low temperatures.