Concreto com cinza de carvão: otimização do traço pelo delineamento Box-Behnken e avaliação eletroquímica frente a Íons Cloret

Abstract

The growing demand for Portland cement in the construction industry imposes significant environmental impacts, driving the search for sustainable alternatives. This study evaluated the feasibility of incorporating fly ash (FA) from coal combustion in thermoelectric plants in the Campanha region (RS, Brazil) as a supplementary cementitious material. The main objective was to optimize the concrete mix with FA using the Box–Behnken design, aiming to maximize mechanical and electrochemical performance against chloride ion ingress. Two FA samples were initially characterized in terms of physicochemical composition, amorphous content, and pozzolanic potential. The sample with higher specific surface area and amorphism (FA-I) was selected for subsequent testing. Concrete specimens with different replacement levels (5%, 10%, and 15%) were produced and tested for compressive strength. Statistical modeling identified the optimal combination of replacement level, water-to-cement ratio, and curing time. The optimized mix was defined as 9.52% replacement with FA I, water-to-cement ratio of 0.53, and 38 days of curing, yielding the best mechanical performance and model fit (R² = 0.925). The optimized mix was further subjected to accelerated corrosion tests under chloride exposure. Results revealed low corrosion current density (icorr), high charge transfer resistance, the formation of diffusive barriers, and a denser microstructure with reduced permeability. These findings demonstrate the technical and environmental feasibility of using FA-I as a mineral addition, highlighting the benefits of statistical optimization in improving concrete durability and sustainability under chloride attack.