Harvesting Basic Oxygen Furnace Slags As Construction Materials Using CO2 Mineralization And Geopolymerization Processes

Abstract

Basic oxygen furnace slag (BOFS) is an industrial by-product that is generated during the steelmaking process. Its chemical composition is similar to blast furnace slag, which is widely used in clinker production. However, the principal difference is that BOFS contains free calcium oxide (f-CaO) and free magnesium oxide (f-MgO) in its chemical composition. In the presence of water, these free metal-bearing oxides experience volumetric expansion, which causes dimensional instability. Consequently, the utilization of BOFS as a construction material remains challenging. In Kazakhstan, the utilization rate of BOFS is particularly low. The large-scale stockpiling of BOFS in landfills might lead to several environmental issues and pollution. The limited application of BOFS in the local construction industry is primarily due to its inherent volumetric instability arising from f-CaO and f-MgO. Moreover, there is a lack of effective stabilization of BOFS techniques and the absence of a standardized protocol for the application of BOFS as a construction material in Kazakhstan, which constitutes a significant research gap. This study addresses these challenges through a systematic approach aimed at improving the stability and practical utilization of BOFS in construction materials. CO₂ mineralization is a chemical reaction between CO₂ and metal-bearing oxide minerals. During natural weathering, BOFS undergoes carbonation, in which reactive free CaO and MgO gradually react with atmospheric CO₂ and moisture, reducing their reactivity and stabilizing expansion behavior. For this reason, the potential of long-term stockpiled BOFS was investigated as a naturally aged and partially stabilized material. To further enhance dimensional stability and immobilize the remaining reactive phases, geopolymerization was used to form a dense binding matrix around BOFS particles. A performance-based kinetic model was then developed as a practical tool to optimize mixture parameters and determine the minimum alkali activator content required to control harmful expansion. Finally, based on the optimized conditions, mixture designs were developed for practical construction applications, particularly non-autoclaved geopolymer cellular bricks and geopolymer Controlled Low Strength Material (CLSM) incorporating treated BOFS as aggregate...