• GGBS replacement up to 30% improves compressive and flexural strength at later ages (28 and 90 days).
• Chloride ion penetration resistance is significantly enhanced with increasing GGBS content, reducing corrosion risk.
• Microstructural analysis shows a denser interfacial transition zone and lower porosity in GGBS concrete.
• Optimal GGBS replacement level is 30%, providing a balance between mechanical performance and durability.