Citation: Solaimanian, M.; Milander, S. Establishing Density-Based Mix Design for Cold Recycled Asphalt Mixes. Eng. Proc. 2023, 36, 14. https://doi.org/10.3390/ engproc2023036014 Academic Editor: Hosin (David) Lee Published: 3 July 2023 Copyright: © 2023 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/). Proceeding Paper Establishing Density-Based Mix Design for Cold Recycled Asphalt Mixes † Mansour Solaimanian * and Scott Milander Larson Transportation Institute, Pennsylvania State University, University Park, PA 16802, USA * Correspondence: msol@psu.edu † Presented at the Second International Conference on Maintenance and Rehabilitation of Constructed Infrastructure Facilities, Honolulu, HI, USA, 16–19 August 2023. Abstract: Design of emulsified cold asphalt mixes using reclaimed asphalt pavement requires opti- mization of the emulsion and moisture content to achieve either maximum density or a minimum strength level of the mix, and in some cases both. Municipalities and local governments most often lack advanced testing equipment to design the cold mixes based on strength or stiffness results. This study was conducted with the objective of developing a simple mix design process for emulsion- based cold mixes using simple laboratory equipment such as proctor molds which are commonly used for optimization of moisture content for soil compaction. Keywords: asphalt; cold mix; reclaimed asphalt; emulsion; strength; proctor; unit weight; RAP 1. Introduction The usage of RAP in the United States has increased over the years; for example, its use grew from 15.6 percent in 2009 to 21.31 percent in 2020, with an estimated 87 million tons used in 2020 [1]. The use of RAP in the construction of pavements is economical and helps save resources and mitigate associated environmental impacts [2,3]. While most RAP is used in hot-mix and warm-mix asphalt, states have also been utilizing it in cold mixes to some extent. Processes such as cold recycling (CR) and full-depth reclamation (FDR) make use of 100 percent of the previously existing asphalt pavement material in the recycling process to produce new and improved pavement base layers. The CR process can be classified into two types: Cold In-Place Recycling (CIR) and Cold Central Plant Recycling (CCPR). Regardless of the cold recycling technique, the compacted mat needs to undergo a curing process to gain strength. The curing in the field is specified by the amount of water content present in the CR layer. The maximum allowable amount of water in the CR layer before an overlay placement should be limited to 1.0 to 1.5 percent [4]. Various approaches have been taken for the design of cold mixes and optimization of the needed emulsion and water content. The most rational design protocols include some measure of the mix engineering properties, such as stiffness or strength. An example of such can be found in the design process developed by Solaimanian et al. [5]. However, there is a lack of adequate testing equipment or manpower at the local level in some municipalities and counties to develop a mix design based on mechanical testing. This research was undertaken to address this problem through a simple design system. The objective was to develop general guidelines for use by maintenance and local forces in determining the necessary emulsion and water content to be blended with RAP in cold recycling work without the need for an elaborate mix design system. 2. Materials Five sources of RAP were included in the study. Initial characterization of RAP in- cluded determination of the binder content, black rock gradation, and extracted aggregate Eng. Proc. 2023, 36, 14. https://doi.org/10.3390/engproc2023036014 https://www.mdpi.com/journal/engproc