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• SBAS increases the compressive strength and chloride penetration resistance of concrete. • Hydration of slag cements can be activated by SBAS. • SBAS delays the depassivation of reinforcing steel (corrosion retardant). • Incorporation of SBAS up to 30% leads to a corrosion propagation similar to that observed for the reference concrete. Despite their growing popularity in the construction industry, cement-based materials containing blast-furnace slag may be subject to various deteriorative processes including corrosion susceptibility owing to the reduced alkalinity of the cementitious matrix. Sugarcane bagasse ash sand (SBAS), the main agro-industrial waste in sugar and ethanol production, has the potential to enhance concrete durability. This study aims to evaluate the effect of SBAS as a fine aggregate on the corrosion of reinforced slag cement concrete. Mixes with different proportions were analysed in terms of mechanical characteristics, chloride penetration, electrolytic conductivity of pore solution, corrosion potential (by open circuit potential), and corrosion rate (by polarisation curves and Tafel plot technique), as well as the analysis of the corroded steel bars (by scanning electron microscopy technique). This paper argues the efficiency of SBAS in retarding corrosion up to an optimal content of approximately 30%. SBAS can refine micropores and act as an alkaline activator of slag cements, leading to increased compressive strength, reduced chloride penetration depth, and delayed corrosion initiation. Above 30%, the corrosion rate increases, which could be owing to the modified microstructure and higher electrolytic conductivity of SBAS-concrete pore solutions, that control the susceptibility of chloride attack on the steel bars. [ABSTRACT FROM AUTHOR]