Citation: El-labbad, E.M.; Heneash, U.; El-Badawy, S.M. Investigation of Waste Electrical Power Plant Oil as a Rejuvenating Agent for Reclaimed Asphalt Binders and Mixtures. Materials 2022, 15, 4811. https:// doi.org/10.3390/ma15144811 Academic Editor: Francesco Canestrari Received: 20 May 2022 Accepted: 4 July 2022 Published: 10 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Investigation of Waste Electrical Power Plant Oil as a Rejuvenating Agent for Reclaimed Asphalt Binders and Mixtures Eman M. El-labbad 1 , Usama Heneash 1 and Sherif M. El-Badawy 2, * 1 Civil Engineering Department, Faculty of Engineering, KafrEl Sheikh University, Kafr El Sheikh 33516, Egypt; emanellabad@yahoo.com (E.M.E.-l.); usama.heneash@eng.kfs.edu.eg (U.H.) 2 Highway and Airport Engineering Laboratory, Public Works Engineering Department, Faculty of Engineering, Mansoura University, 60 Elgomhoria St., Mansoura 35516, Egypt * Correspondence: sbadawy@mans.edu.eg; Tel.: +20-100-018-3519; Fax: +20-50-220-2251 Abstract: One of the main difficulties with employing recycled asphalt pavement (RAP) in hot mix asphalt (HMA) is bitumen aging; hence, the percentage of RAP in the HMA is limited. This research evaluates the rheological properties of the RAP binder and the performance of HMA containing high RAP content using waste engine oil (WEO) from an Electrical Power Plant as a rejuvenator. The rheological and microstructural properties of the RAP binder and rejuvenated RAP binder were determined in the laboratory. Both the recycled and rejuvenated recycled mixes were tested for Marshall stability, indirect tensile strength, dynamic modulus (E*), and flow number tests. The RAP binder was recovered using two different processes: rotavapor distillation followed by centrifugation (RCRD) and column distillation without centrifugation (RNCCD). The optimal WEO percentages for the RCRD and RNCCD recovery procedures were 0.5% and 3%, respectively. The Marshall test results revealed that adding WEO to the recycled mix enhanced its stability and flow compared to the control mix. The rejuvenated mix containing recovered binder from the RCRD recovery process was found to be better than the rejuvenated mix containing recovered binder from the RNCCD recovery process. The rejuvenated recycled mixes outperformed the recycled mix in terms of moisture resistance, which was evidenced by tensile strength ratio values of 0.88, 0.90, and 0.91 for the control and 0.5% and 3% WEO modified mixes, respectively. Finally, the results of dynamic modulus and flow number testing revealed that the rejuvenated mixes had a modest drop in both the dynamic modulus and flow number compared to the non-rejuvenated mix. Keywords: RAP; WEO; master curve; FTIR; dynamic modulus; flow number 1. Introduction Bitumen is one of the most often utilized bonding materials for asphalt pavement [1]. Approximately 95% of globally produced bitumen each year is used by the paving industry sector [2]. Declining supplies of locally accessible good-quality aggregates, rising waste disposal concerns, and rising bitumen prices have resulted in higher usage of recycled as- phalt pavement (RAP) in the construction of infrastructure projects [3]. Recently, pavement recycling has gained prominence in developing countries. The recycling of pavements includes the incorporation of discarded or damaged materials for new pavement construc- tion [4]. The mix design process takes into account the amount of bitumen in RAP when the amount of RAP used in hot mix asphalt (HMA) reaches 25% or more [5]. Moisture damage, fatigue, and thermal cracking are almost certain to occur in recycled high-RAP content mixes, where they become stiff due to the aged bitumen. Consequently, characterization of the RAP binder and aggregate is a crucial step in the design [6,7]. Earlier studies have demonstrated that after the asphalt pavement life cycle has ended, the bitumen and aggregate from the old pavement are still significant resources [8]. Aging Materials 2022, 15, 4811. https://doi.org/10.3390/ma15144811 https://www.mdpi.com/journal/materials