Evaluation of the Cashew Nut Shell Liquid (CNSL) antioxidant characteristics for asphaltic materials using different aging procedures

Abstract

The asphalt cement (AC) aging is a natural process mainly caused by volatilization of lighter fractions and oxidation reactions. It is known that, over the years, the asphalt mixtures age and become more rigid. This stiffening may decrease the fatigue crack resistance in asphalt pavements, and thus, can make them more resistant to permanent deformation. The cashew nut shell liquid (CNSL) is a "green additive", coming from a renewable and biodegradable source and has antioxidant characteristics. In the literature, there are some studies that highlight the CNSL antioxidant characteristics, however, few consider its application in paving services. In this study, the CNSL is proposed as a modifier of the AC 50/70 for the purpose of assessing their antioxidant potential. The asphalt mixes, the conventional AC and the AC modified with 2% of CNSL were analyzed before and after various aging processes. The asphalt mixtures were aged in different conditions: compacted and loose samples. After the aging processes and the AC recovery, they were evaluated in relation to their empirical and rheological properties and compared with those obtained for the virgin AC. Furthermore, the effects of oxidative aging was analyzed by infrared spectroscopy - FTIR (Fourier Transform Infrared) and changes in the SARA composition (Saturates, Aromatics, Resins and Asphaltenes) through chromatography. The asphalt mixtures containing conventional AC and AC modified with 2% of CNSL, after the aforementioned processes of aging, were characterized mechanically using resilience modulus (RM), tensile strength (TS), fatigue life, dynamic modulus and flow number (FN). The results for the AC tests indicate that the CNSL acts as an antioxidant for the short-term period, but it does not show the same behavior for the long-term period. After analyzing the results achieved for the asphalt mixtures, it can be said that the CNSL caused a slight reduction in stiffness of these mixtures and, possibly, it was polymerized when subjected to the oven aging process. The most aggressive process of aging was obtained when subjecting the loose mixture to the long-term aging for nine days.