RSM-based evaluation of mechanical and durability properties of recycled aggregate concrete containing GGBFS and silica fume Alireza Habibi a , Amir Mohammad Ramezanianpour b , Mahdi Mahdikhani c,⇑ , Omid Bamshad b a Faculty of Environment, College of Engineering, University of Tehran, Tehran, Iran b Faculty of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran c Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran highlights  The effect of GGBFS and SF in RAC are presented using RSM.  RSM is an efficient method for predicting and optimizing the properties of RAC.  Some equations for prediction of properties of RAC are presented.  The equations provided an excellent correlation between variables and responses. article info Article history: Received 14 July 2020 Received in revised form 11 October 2020 Accepted 20 October 2020 Available online xxxx Keywords: Response surface method Optimization Recycled aggregates Bulk Electrical Conductivity (BEC) Compressive strength (CS) Rapid Chloride Penetration Test (RCPT) Capillary water absorption abstract Concrete is the most consumed material in the construction industry, and using recycled concrete aggre- gates (RCA), silica fume (SF) and ground-granulated blast-furnace slag (GGBFS) in concrete could reduce its negative environmental impacts by preserving natural resources and reducing construction and demolition (C&D) waste generation and CO 2 emissions. Optimizing the mix design based on both mechanical and durability properties of RAC has not been performed. In this study, the mechanical prop- erties and durability of Recycled Aggregate Concrete (RAC) containing GGBFS and Silica Fume (SF) were evaluated via Response Surface Methodology (RSM). The GGBFS was used to reduce the environmental pollution caused by cement production and balancing the negative effect of RA on the mechanical prop- erties of concrete. The results indicated that RA had a negative effect on durability properties of concrete at 7 and 28 ages, while it had no effect on the properties at 90 days. Finally, optimized mix designs were obtained based on two specific scenarios. In the first scenario, the mix design with the highest of both mechanical and durability properties was obtained. In the second one, a mix design with the highest amounts of GGBFS, SF and RA, was achieved, due to the environmental issues related to concrete production. Ó 2020 Published by Elsevier Ltd. 1. Introduction A great portion of the solid wastes generated in the world is Construction and Demolition (C&D) waste, such that it consists 31% of the annual solid waste in the European Union [1]. On the other hand, the main constituent of concrete, as the mostly used material in construction, is aggregates, comprising approximately 70–80% of its volume. Furthermore, resources of Natural Aggre- gates (NA) are unrenewable and ecological concerns about mining of aggregates including water pollution, erosion in the river bank, etc., have been raised [2]. One of the global efforts to reduce the CO 2 emissions caused by cement production is the use of supple- mentary cementitious materials (SCMs) such as silica fume, ground-granulated blast-furnace slag (GGBFS), and natural poz- zolans, which besides their environmental benefits, also have a positive effect on the long-term mechanical and durability proper- ties of concrete [20–22]. Recycled aggregate concrete (RAC) has been recognized as a sustainable substitution to ordinary natural aggregate concrete, addressing the concerns about global sustainability issues includ- ing vast consumption of natural resources and extreme amount of construction waste generation [3]. Also, a series of procedures and standards have been developed to facilitate the production https://doi.org/10.1016/j.conbuildmat.2020.121431 0950-0618/Ó 2020 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail addresses: alirezahabibi@ut.ac.ir (A. Habibi), ramezanian@ut.ac.ir (A.M. Ramezanianpour), mahdikhani@eng.ikiu.ac.ir (M. Mahdikhani), Omid.bamshad@ ut.ac.ir (O. Bamshad). Construction and Building Materials xxx (xxxx) xxx Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Please cite this article as: A. Habibi, Amir Mohammad Ramezanianpour, M. Mahdikhani et al., RSM-based evaluation of mechanical and durability properties of recycled aggregate con- crete containing GGBFS and silica fume, Construction and Building Materials, https://doi.org/10.1016/j.conbuildmat.2020.121431