Evaluating and selecting the best sustainable ‎concrete mixes based on recycled waste materials

Sustainable concrete is considered a very important material in building construction in terms of achieving sustainability pillars and improving its properties. It includes many recent types of construction concrete wastes, natural recycled wastes, and mineral materials. These sustainable concrete types are governed by several criteria leading to difficulty in determining the best. In this research, a sustainable concrete selection decision-making model (SCSDMM) was developed to support the selection of the best sustainable concrete by applying two modules. Module 01 utilized the fuzzy logic technique for evaluating the proposed criteria, which are controlled by several factors using logical rules for relating factor weights. Module 02 was based on the analytic hierarchy process (AHP), considering applying sustainability principles and aimed to support the final decision for determining the best sustainable concrete‎. The proposed model dealt with nine replacement materials to produce sustainable concrete mixes as alternatives. The comparison criteria included many characteristics of compressive strength, tensile strength, low water absorption, low environmental impact, cost savings, and recycled materials availability. The model was applied using data from two case studies in the Kingdom of Saudi Arabia (KSA) and Egypt. The results showed that compressive ‎strength ‎and low water absorption were rated as the most important criteria, while the importance of recycled materials availability represented the lowest‎. ‎The final decision favored using recycled natural powder (RNP) in KSA, followed by fine recycled concrete aggregate (FRNA). At the same time, silica fume (SF) was supported to be used preferably in Egypt, followed by fine recycled concrete aggregated (FRCA). To evaluate the model's robustness, sensitivity analysis tests were conducted to measure the effects of modifying criteria and alternatives' relative weights on the final decision. The SCSDMM can accept more concrete mixes alternatives and criteria as well as it can also be applied in other countries.