Copyright © 2023 the Authors. This is an open-access article distributed under the creative commons attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited. 1. Introduction Population growth, continuous industrial development, construction of infrastructure and house-building activities create huge amounts of construction and demolition (C and D) waste and hence, the dire need for waste recycling. The construction industry is a major consumer of natural resources and the global aggregate production almost doubled from 21 billion tons in 2007 to 40 billion tons in 2014. Countries such as China, India, Indonesia, Malaysia, Thailand, Gulf States, Turkey, Russia, Brazil and Mexico have recorded some of the strongest increases in the demand for waste recycling. Hence, the progressive depletion of natural resources and growing awareness of sustainable waste management by developed and emerging economies, have given ever-increasing relevance to recycling and re-using C and D waste in civil engineering projects [1]. The replacement of aging infrastructures and buildings results in large quantities of construction waste, especially concrete waste. Concrete waste generated from demolition work contains many aggregates. Because aggregates occupy the majority of the concrete volume, it is reasonable to investigate reusing the aggregates from concrete waste to create new concrete [2-4]. Recycled coarse aggregates (RCA) have been used in many laboratory experiments [5-7]. Due to the potential economic and environmental benefits, interest in technology for processing waste concrete and the use of RCA is rapidly increasing [8], [9]. The advantages of using RCAs include a reduction in the use of natural coarse aggregate (NCA) resources and a decrease in the amount of waste disposed of in landfills, thereby diminishing environmental pollution. Despite the high demand, RCAs are primarily used in road bases and nonstructural concrete. Only a small percentage of RCAs are used in structural concrete because the quality of RCAs is less reliable than that of NCA. Comprehensive experimental research has been performed to assess the properties of both NCA and RCA concrete at the material level [10-15]. Recycled concrete aggregates (RCA) are made of natural aggregates (NA) and cement mortar adhered to the latter. The main difference between the two types of aggregates is the presence of cement mortar in RCA. This mortar increases the RCA’s surface roughness, porosity and water absorption compared to NA, but decreases their mechanical properties [16]. The incorporation of RCA in concrete, due to their higher water absorption, requires a higher apparent water/cement ratio in order to keep workability constant. This procedure can affect the properties of concrete, moreover when the replacement ratio of NA by RCA increases and the fine fraction of the aggregates is replaced [16], [17]. The compressive strength, the tensile strength and, even more, the modulus of elasticity tend to decrease with the incorporation of RCA [18], [19]. The durability, shrinkage and creep of concrete are also usually negatively affected by the incorporation of RCA [20], [21]. However, some studies have reported lower cracking loads and wider cracks in elements made of recycled aggregate concrete [24]. According to Basrah Journal for Engineering Sciences, Vol. 23, No. 1, (2023), 26-32 Original Article Journal homepage: www.bjes.edu.iq ISSN (Online): 23118385, ISSN (Print): 18146120 Structural Behavior of Reinforced Concrete Hollow Core Slabs Cast with Self-Compacting Concrete Containing Recycled Concrete as Coarse Aggregate Mustafa Raheem Hassan 1, *, Jamal Abdulsamad Khudhair 2 1,2 Department of Civil Engineering, College of Engineering, University of Basrah, Basrah, Iraq E-mail addresses: mostafa_rheem90@yahoo.com , jamal.khudhair@uobasrah.edu.iq Received: 17 July 2022; Accepted: 9 November 2022; Published: 2 July 2023 Abstract This paper investigates the possibility of recycled aggregate use in concrete slabs with hollow cores. The main variables considered in the experimental study for the slabs were the recycled aggregate percentage and the hollow core number. Six slabs with dimensions of (1000 × 500 × 120) mm was fabricated and tested. The results showed that the addition of recycled aggregate in the concrete slabs affected the ultimate strength, ductility, and energy absorption of the concrete members. An increase of the recycled aggregate percentage to 25 % decreased the ultimate strength capacity by 3.54 %, but the increase of recycled aggregate to 50 % led to a decrease in the ultimate strength of about 6.64%. The existence of a hollow core reduced the cracking and ultimate load capacity of the RCA slabs, and this reduction was according to the core number which the fabrication of more cores caused more decrement. The ductility and energy absorption were decreased when the replacement ratio of the recycled aggregate increased. Also, the core number affected the ductility and energy absorption. The energy absorption was the most property affected by the core number increase which caused an average reduction of 71.5 % when the core number increased from two to three hollow cores. Keywords: Hollow-core slabs, Self-compacting concrete (SCC), Recycled concrete aggregate (RCA). © 2023 The Authors. Published by the University of Basrah. Open-access article. https://doi.org/10.33971/bjes.23.1.4