# Effect of Chemical Composition of Bio- and Petroleum-Based Modifiers on Asphalt Binder Rheology
## 1 Introduction  
Asphalt concrete (AC) is one of the most commonly used pavement materials in the United States and worldwide. More than 400 million tons of AC are produced in the US annually, which requires 20 million tons of asphalt binder [1]. AC mixture is a heterogeneous composite of asphalt binder, mineral aggregates, and air voids. The performance of AC mixtures is greatly affected by aggregate characteristics, binder chemistry and rheology, mixture volumetrics, and aging. Aging of AC is acontinuous process; it is dominated by volatilization and oxidation of asphalt binder in the short- and long-term, respectively. Volatilization in binders refers to loss of lighter fractions when exposed to high temperatures and occurs during the production and construction stages. Oxidation in binders is caused by photo-oxidation and thermal oxidation during pavement's service-life [2]. Aging increases AC britteness that may result in cracking. Hence, binders with superior aging resistance characteristics may delay AC cracking and increase pavement service life. Asphal binder (AB) is an important component for the construction of AC pavements. It is currently produced from the fractional distillation of crude petroleum at refineries. In recent years, the increasing use of harder and aged recycled asphalt materials in pavement applications has significantly increased the need for softer ABs [1]. Logistical limitations and the cost of refineries to produce softer ABs instead of products of higher financial value, result in a shortage of soft straight-run or unmodified AB in the market [3]. To overcome the current demand for softer ABs, traditional petroleum-based \"softeners\", like AB flux and aromatic oils are blended with straight-run AB [4]. Blending \"softeners\" with readily available products, like recycled oils and bio-based oils, provides an opportunity to manufacture required AB economically and reduce the dependence on petroleum-based products. A variety of proprietary products are available to modify AB to achieve softer grades. They are used with limited knowledge about their long-term performance. Poor durability and/or extended cracking issues have been identified when re-refined engine oil bottoms (ReOB) and waste engine oils (WEO) have been blended in AB [5; 6; 7; 8; 9]. On the other hand, use of certain bio-based oils in ABs increases the oxidation potential which makes pavements vulnerable to cracking over the long-term [10]. This limits or restricts the use of these products. However, there are some specialized bio-based softeners that have shown enhanced long-term performance of ABs and reduced cracking potential [11]. Therefore, the potential of bio-based modifiers to produce softer PGs is investigated in this study. A ReOB-based modifier was included in this study for comparison purposes. Superpave Performance Grading (PG) is a rheology-based system, currently used to trade and specify AB in the United States. The PG system has limitations in identifying long-term performance of modified asphalt binder (MAB). The use of bio-based modifiers can significantly impact AB chemistry and rheology without changing its Superpave grading. The current challenges for the market-entry of MAB are: (i) their complex chemistry, (ii) their uncertain long-term rheological performance, and (iii) the lack of a robust grading system that can discriminate them to ensure long-term performance. Low-temperature performance of AB is critical to prevent adverse effects of thermal cracking. Use of recycled asphalt pavements (RAP)--obtained from milling of old asphalt layers--and recycled asphalt shingles (RAS)--typically obtained from either tear-off shingles or manufactured waste shingles--has increased in AC pavement and requires adequately-performing binders to avoid premature cracking [12; 13; 14; 15; 16; 17; 18]. The \(\Delta\)T\({}_{\rm c}\) parameter has been used to assess the low-temperature induced cracking performance of AB [19; 20]. Low-temperature ductility of AB has been related to pavement cracking performance [21].