ASSESSING THE EFFECTIVENESS OF ANTIOXIDANT ADDITIVES IN MITIGATING AGING EFFECTS ON BITUMINOUS MIXTURES

Abstract

Oxidative aging of bitumen is a non-ending and irreversible phenomenon. It primarily causes stiffening of binder, which eventually makes the pavement embrittle and highly susceptible to cracking. This, in turn, reduces its ability to withstand high traffic loads and thermal stresses, ultimately leading to premature pavement failure. Therefore, to enhance the durability and service life of pavement, it is essential to slow down the oxidation mechanism. Presently, the pavement research community is exploring various possible techniques to mitigate the impact of aging. One such method involves modification of bitumen by incorporation of antioxidants additives which are capable of inhibiting the chemical oxidation reaction. Antioxidants are widely recognized as promising chemical compounds that function as sacrificial or trapping agents and break the oxidation chain reaction. In this study, a primary antioxidant (Irganox 1010) was incorporated in the conventional binder (VG 30). The bituminous mixtures were prepared for dense bituminous macadam (DBM-II) and bituminous concrete (BC-I) gradations. The effect of modification on the performance of bituminous mixtures was analyzed in the unaged and aged conditions. Performance tests including moisture susceptibility, stiffness, fatigue resistance, and rutting characteristics, were conducted on the control and modified mixes. A parameter known as the “aging index” was determined to quantify the aging resistance of mixtures after modification. Results indicated that for both the gradation, the bituminous mixtures prepared with the addition of 0.4% (by weight of binder) of Irganox 1010 in VG30 exhibited lower aging. The modified mixes showed higher TSR values, indicating improved moisture resistance. After aging, the moisture resistance of modified samples were higher than control samples. The AI value was found to be 4% for BC and 15% for DBM lower for modified mixtures. Moreover, the resilient modulus (Mr) decreased by 21.33% for BC and 15.56% for the DBM modified mixes after aging. This shows that antioxidant decreases the bitumen hardening. Similarly, the rutting performance of modified mixes for both the gradations were satisfactory. After aging the samples with Irganox 1010 were found to be more ductile and hence are expected to have improved fatigue life. However, several discrepancies in the results of fatigue test were observed. In summary, the incorporation of antioxidant was found to improve the aging resistance of bituminous mixtures, satisfying the performance criteria of conventional mixes. It is suggested to investigate other types of commercially and naturally obtained antioxidant additives with different binders.