  Citation: Godat, A.; Alghafri, E.; Al Tamimi, N.; Aljaberi, H.; Aldaweela, S. Bond Behavior of Basalt Fiber Reinforced Polymer Bars in Recycled Coarse Aggregate Concrete. Sustainability 2022, 14, 1374. https://doi.org/10.3390/su14031374 Academic Editors: Marwa Hassan and Syed Minhaj Saleem Kazmi Received: 22 November 2021 Accepted: 12 January 2022 Published: 25 January 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/). sustainability Article Bond Behavior of Basalt Fiber Reinforced Polymer Bars in Recycled Coarse Aggregate Concrete Ahmed Godat *, Ebtesam Alghafri, Noura Al Tamimi , Hamda Aljaberi and Shaima Aldaweela Department of Civil and Environmental Engineering, United Arab Emirates University, Al-Ain 15551, United Arab Emirates; 201504160@uaeu.ac.ae (E.A.); 201511497@uaeu.ac.ae (N.A.T.); 201502167@uaeu.ac.ae (H.A.); 201500694@uaeu.ac.ae (S.A.) * Correspondence: Ahmed.Godat@uaeu.ac.ae Abstract: This study is an experimental investigation of the bond stress–slip behavior of BFRP bars in recycled coarse aggregate concrete using the pull-out experiment. The experimental program contains twenty-three BFRP specimens and twelve specimens with GFRP bars. The pull-out test results of the BFRP and GFRP specimens in recycled coarse aggregate concrete are balanced to those of normal coarse aggregate concrete, which are used as a benchmark. In this study, the influence of major parameters on the BFRP bond performance are investigated: concrete strengths (30, 45, and 60 MPa), bar diameter (8, 10, and 12 mm), and bar bond length (5, 10, and 15d, where d is the diameter of the bar). The effect of the parameters considered is determined on the basis of the increase in the bond resistance. The test findings showed that the bond resistance of BFRP bars in recycled coarse aggregate concrete is highly comparable to that of normal aggregate concrete. In addition, the BFRP bar pull-out failure is not governing when a bar bond length of 10 or 15d, or high concrete strength of 45 or 60 MPa, is utilized. Theoretical equations from the literature that predict the bond resistance and bond stress–slip performance for FRP reinforced concrete are compared to the experimental results of this study. It is found that the equation described by Orangun and colleagues can accurately predict the bond resistance for BFRP bars in recycled coarse aggregate concrete with an average of 86% compared to the experimental results. Keywords: BFRP bars; GFRP bars; direct pull-out test; recycled coarse aggregate; concrete strength; bond resistance; bond stress–slip relationship; theoretical equations 1. Introduction Basalt fiber reinforced polymer (BFRP) is a fairly new concept to FRP and composites. Recently, BFRP bars emerged as an option to replace glass FRP (GFRP) bars in reinforced concrete. Although basalt fibers are manufactured using the same technology for E-glass fiber, its manufacturing technique uses less energy, and basalt rocks may be found all over the world. Basalt fibers are slightly stiffer and stronger than E-glass, environmentally safe, non-toxic, non-corrosive, nonmagnetic, and have high heat stability and insulating characteristics [1–5]. Basalt fibers are characterized by their high strength to alkalinity, which can be found in concrete [4], excellent resistance to high temperature and moisture conditions [4,6], high chemical stability [7,8], and outstanding fatigue resistance [9]. Although the BFRP has received broad acceptance by the engineering community, a limited number of research studies have been carried out to investigate the use of BFRP in structural applications [10–23]. The bond performance is an essential aspect that gov- erns the capacity, serviceability, and ductility of concrete structures [24–26]. El Refai and colleagues [27] investigated the bond performance of BFRP bars in high concrete compres- sive strength using the direct pull-out test. The test parameters considered in their study included different bar diameters and bond lengths. Their test results were compared to GFRP bars under the same conditions. They concluded that the BFRP bond resistance is Sustainability 2022, 14, 1374. https://doi.org/10.3390/su14031374 https://www.mdpi.com/journal/sustainability