Effect of Antioxidant Additives and Restorators on Performance of Asphalt Binders

The use of recycled materials, such as reclaimed asphalt pavement (RAP), recycled asphalt shingle (RAS), glass, and ground tire rubber, is a cost-effective and environmentally-friendly production method in the asphalt paving industry. The effects of recycled materials on asphalt mixtures have been investigated and reported by many researchers [1-4]. An extensive literature review reveals that the increase in stiffness, which is due to the aged asphalt binder present in RAP, is the main drawback caused by introducing RAP in asphalt mixtures [1, 5]. On the other hand, RAP in asphalt mixtures can result in an improvement in the rutting resistance of RAP blended mixtures [5-7]. The aging of an asphalt binder has a direct relationship with the stiffness and durability of asphalt mixtures [8-11]. The use of restoration agent (RA) (i.e., rejuvenators or softening agents) have gained popularity in recent years since they can effectively restore the engineering properties (e.g., stiffness) of the aged asphalt binder. The National Center for Asphalt Technology (NCAT) has categorized these chemical additives (i.e., RAs) into five main groups based on their origins and production process: (1) Paraffinic Oils, (2) Aromatic Extracts, (3) Naphthenic Oils, (4) Triglycerides & Fatty Acids, and (5) Tall Oils. Currently, there is general agreement that RAs can improve the cracking resistance and diminish the rutting resistance of the RAP blended mixtures. However, there are some concerns about the effect of RAs on the moisture damage resistance [12] and the long term performance (aging) of these additives. For instance, Haghshenas et al. [13] evaluated the long-term performance of three chemically different RAs (i.e., petroleum-, tall oil- and agriculture-based). They reported that the tall oil- and agriculture-based additive did not mitigate the effects of long-term aging and tall oil RA increased the moisture sensitivity of the mixtures, however, the immediate performance of these RAs was acceptable and was a lower cost alternative than petroleum-based. On the other hand, there are additives that are used to modify asphalt binder and mitigate the age hardening. These modifiers are called antioxidants or antiaging additives. When antioxidants are added to asphalt, they control oxidation by trapping or scavenging free radicals which are responsible for initiating and/or propagating oxidation [14]. Recently, some researchers carried out several rheological (e.g., dynamic shear rheometer (DSR) and bending beam rheometer (BBR)) and mechanical (e.g., resilient modulus, indirect tensile strength, creep, and fatigue resistance) tests to study the effect antioxidant additives on asphalt binder and mixture performance [15-18]. For instance, Apeagyei et al. [19] investigated the effect of an antioxidant additive, which was produced by combining aldehyde, thioester, and a caltalyst; on performance of a binder. They reported that the antioxidant additive not only increases the dynamic modulus and boosts the permanent deformation resistance of the asphalt mixture, it also enhances the low temperature cracking resistance after both short-term and long-term oven aging conditioned. More than that, Williams and McCready [20] examined the effect of agriculturally derived lignin containing 3–12% ethanol coproducts using DSR and BBR. The claimed that the agriculturally derived lignin might be used as an antioxidant additive to retard the oxidation process occurs for the binder/mixture after short- and long-term aging. Unfortunately, there is no guideline for RAs and antioxidants selection and laboratory protocol to examine their effectiveness on performance of asphaltic materials. On the other hand, the possible incorporation of RAs and antioxidant additives in asphalt binders and mixtures can provide huge economical, technical, and environmental benefits; however, the combination of these additives and their long-term effectiveness have not been fully investigated. As a result, the phase I of this research will focus on the effect of chemical properties of RAs on rheological and mechanical properties of asphaltic materials, especially, on long-term performance of asphalt binders and mixtures. In addition, the long-term performance of the restored binders modified by one type of antiaging will be examined. Finally, the combination effect of RAs and antioxidant additive will be evaluated in two different levels: mixture and binder. The results of this research may result in a guideline for RAs and antioxidants selection and developing a laboratory testing protocol to evaluate the performance of the binders modified by RAs and antioxidants. This research aims to investigate the effect of various RAs and one antioxidant additive on performance of asphalt binders and mixtures. Testing will be performed on various blends of RAs and antioxidants containing laboratory aged materials (up to 100%). The laboratory tests will be performed to evaluate chemical properties (e.g., SARA, FTIR, elemental analysis) of the additives and binders, rheological performance (e.g., PG, Glover-Rowe) of the binders, and mechanical properties (e.g., SCB and TSR) of the mixtures. In addition, the possible correlation between chemical characteristics of the additives and rheological/mechanical properties of the binders/mixtures will be examined.