Durability properties and steel corrosion resistance of reinforced concrete using fly ash and ground granulated blast furnace slag as partial replacements for sand and cement

Highly corrosion-resistant concretes are required to enhance the durability of civil structures in coastal regions. Also, reusing by-products as sand or cement replacement in cement composites is urgent due to demands and shortage of river sand, CO₂ emission from the cement industry, and increasing FA or GBFS amount in thermal power plants, detrimental to environments and requiring disposal solutions. Hence, this paper investigated the effects of incorporating FA as a partial replacement for river sand from 20 to 60% and utilizing GBFS to replace 30% of cement on the corrosion resistance of steel in concrete. The experimental findings showed that the by-products reduced the pH value of fresh cementitious mixtures, increased compressive strength, lowered water absorption, and densified the microstructure of FA/GBFS-modified concrete. In particular, the resulting cement composites demonstrated a significant reduction in Chloride ion penetration and corrosion current, increasing the deterioration occurrence time due to steel corrosion by around 2.29–2.43 times compared to control concrete. Also, corrosion cracking on concrete surfaces and around steel bars of the modified concrete was significantly reduced. Pearson correlation finally emphasized the positive impact of FA and GBFS as sand and cement replacements on the durability of reinforced concrete exposed to Chloride-rich environments. Concrete with 20–60% FA and 30% GBFS exhibited excellent corrosion resistance, ideal for coastal construction.