Incorporating Waelz Slag to Strengthen the Properties of Fine Recycled Aggregate Concrete

The use of recycled aggregates in concrete is the foremost step towards accomplishing sustainability and circular economy in the construction industry. However, the main drawback of using recycled aggregates is the inferior quality of the resulting concrete. This limits higher than 30 % replacement of natural aggregate with fine recycled concrete aggregates (FRCA). This work attempts to improve the mechanical and durability performance of FRCA concrete by incorporating Waelz slag, which is a waste material obtained from the zinc refining industry. The influence of replacing up to 75 % FRCA with Waelz slag was analysed by assessing the mechanical properties, durability properties, microstructure, and leaching of toxic metals. The results were encouraging as all concrete mixes showed improved performance by incorporating Waelz slag. A comprehensive analysis revealed that a combination of 50 % FRCA and 50 % Walez slag is most effective as it exhibited higher improvement in mechanical and durability properties with a dense interfacial transition zone in comparison to control. The leaching of heavy metals from concrete was within the permissible limits in all the concrete mixes. The study showed that the incorporation of Waelz slag balances the shortfalls of FRCA, enhances the overall performance of concrete, and addresses the circular economy in a significant way.