Citation: Hubert, J.; Zhao, Z.; Michel, F.; Courard, L. Effect of Crushing Method on the Properties of Produced Recycled Concrete Aggregates. Buildings 2023, 13, 2217. https://doi.org/10.3390/ buildings13092217 Academic Editor: Jan Foˇ rt Received: 25 July 2023 Revised: 28 August 2023 Accepted: 28 August 2023 Published: 31 August 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/). buildings Article Effect of Crushing Method on the Properties of Produced Recycled Concrete Aggregates Julien Hubert 1 , Zengfeng Zhao 2, * , Frédéric Michel 1 and Luc Courard 1 1 Urban and Environmental Engineering, University of Liège, Allée de la Découverte 9, 4000 Liège, Belgium; julien.hubert@uliege.be (J.H.); frederic.michel@uliege.be (F.M.); luc.courard@uliege.be (L.C.) 2 Department of Structural Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China * Correspondence: zengfengzhao@tongji.edu.cn Abstract: Construction and Demolition Waste (C&DW) is generated around the world and its quantity will increase in the future. Recycling has become the favored method of dealing with concrete waste but, to avoid its downcycling, it is important to develop a recycling process which is able to produce high-grade recycled concrete aggregates (RCA). To that end, studying the influence of the production process on the properties of RCA can prove to be a crucial step toward a more circular construction industry. In this study, the influence of the crushing method is investigated. Samples of five laboratory-made concretes have been crushed using the most common mechanical crushing methods (impact crusher and jaw crusher), and the particle size distribution, morphology, hardened cement paste content and water absorption of the produced RCA have been measured and analyzed. The findings indicate that the use of impact crushers results in the production of RCA possessing more spherical geometric characteristics, albeit with a broader particle size distribution and a relatively higher content of fine particles as compared to those obtained from jaw crushers. Additionally, it is observed that the employed crushing technique seemingly exerts no discernible impact on the hardened cement paste content and the water absorption in the context of the studied concretes. Keywords: construction and demolition waste; recycling; crushing; recycled concrete aggregates; morphology; water absorption 1. Introduction The ongoing expansion and replacement of existing real estate leads to the production of important amount of Construction and Demolition Wastes (C&DW). The construction industry is responsible for one of the heaviest and most voluminous waste streams in the EU [1]. It accounts for at least one third of the waste generated in the EU and represents an amount of about 850 Mt (Mt: Megaton). The most widely used building material is concrete with a global production increasing by as much as 25 Gt (Gt: Gigaton) per year [2,3] which means that most of the C&DW are composed of concrete. Due to environ- mental and economic pressure, recycling has become an increasingly popular method of disposing of C&DW that can provide a sustainable source of aggregates for future concrete production [4–6]. Recycling C&DW starts with the selective demotion of a building to separate the different waste materials [7,8] after which it is transferred to the recycling plant. C&DW recycling plants bear a resemblance to natural aggregate production facilities, as they employ a range of equipment such as crushers, screens, transfer devices and filtering systems to produce granular materials of a predetermined grain size distribution. The degree of processing of the C&DW depends on their intended future application [9]. The recycling plants can be divided into mobile or stationary styles. Considering fixed recycling plants [10,11], the recycling process starts with the reception and storage of the materials to Buildings 2023, 13, 2217. https://doi.org/10.3390/buildings13092217 https://www.mdpi.com/journal/buildings