# Physical and Chemical Methods to Assess Performance of TPO-Modified Asphalt Binder
## 1 Introduction  
Different materials have been used over the years as asphalt binder additives [1, 2, 3]. Oils are one of the biggest categories of asphalt additives. Oil additives can enhance asphalt performance by reducing binder stiffness [4]; however, oils can also make binders too soft, reducing their high-temperature performance [5]. Tire pyrolysis oil (TPO) is obtained by heating times between 300 and 1000 \({}^{\circ}\)C without the presence of oxygen. Although many studies have focused on using pyrolysis to produce liquid fuels [6, 7, 8], recently, some studies have added pyrolysis oils into asphalt binders [9, 10, 11, 12]. Chemically dense and reactive additives like TPO are likely to change the physical and chemical performance of the asphalt binder. While the standardized physical performance of materials is important, a standard for chemical evaluation is still needed. This study will use both physical and chemical testing to compare standardized aging performance on TPO-modified binders. Tire pyrolysis oil could be a good asphalt additive if properly processed to contain minimal pollutants and effectively interact with a binder's matrix. Tires have desirable components, but their strong cross-polymerization makes it difficult to separate and maximizeprofitable products [10; 13; 14; 15; 16]. Some tires are physically processed and used recreationally, but this can release environmental pollutants [17]. The chemical processing of tires depends heavily on processing variables like temperature, pressure, heating rate, and residence time [14]. TPO has been tested and chemically characterized, though due to the high variability in the source material and processing, it is unknown how similar TPO compositions are [9]. Catalysts and optimum production parameters are still being developed for a better chemical processing of TPO [13]. While proper processing is an economic investment, there are potential economic advantages. Tires are essential to road systems, creating and maintaining a large feedstock of materials. Additionally, TPO has been used in asphalt binders as a rejuvenator [9; 12]. Rejuvenators can reverse and prevent the effects of aging, making the recycling of pavements economically sustainable. One study found that TPO blends reduced the stiffness of aged binders and enhanced fatigue resistance. Additionally, carbonyl indices, an indication of aging, were reduced with the addition of TPO [9]. Another study found that the rejuvenated binder's storage stability depended on the type of rejuvenator and the aging of the blend. The thermal stability and chemical compatibility of blends are needed for an effective asphalt matrix [18]. While many factors can influence the quality and physical performance of TPO, recycling pavements involves both physical and chemical changes. Therefore, it is important to have more chemical performance testing to understand how aging affects TPO-modified blends. In contrast to the high variability of TPO, an asphalt binder has existing standards to characterize its physical aging. Standardized physical methods like the rolling thin-film oven test (RTFOT) and pressure aging vessel (PAV) are used to compare asphalt binder blends by mimicking short-term and long-term aging in the field, respectively. Modified asphalt is tested via the RTFOT to determine the mass loss and viscoelastic changes due to modeled mixing and compaction. Since some additives have highly volatile components, it is important to see if the additive will remain in the blend or be released into the environment. The stiffness parameter \(\text{G}^{\star}/\text{sin}(\text{8})\) is obtained for unaged and RTFOT-aged samples to determine the high PG temperature. After the RTFOT, PAV testing is conducted to mimic 7-10 years of service life aging. This testing indicates how well the modified blend will perform in the field. The stiffness parameter changes to \(\text{G}^{\star}\text{sin}(\text{8})\) and indicates the intermediate PG temperature.