Enhancement of Mechanical Properties and Durability of Alkali-Activated Slag Concrete through Optimized Alkali Activator Combinations

This research systematically optimizes the use of ground granulated blast furnace slag (GGBFS) as a full replacement for Ordinary Portland Cement (OPC) in alkali-activated slag (AAS) concrete. Initial trials on blended OPC-GGBFS concrete revealed that 20–22% GGBFS replacement yields the best balance of workability, setting time, and compressive strength (>82% of control at 28 days). Beyond 23%, strength declines sharply. Using 22% GGBFS-based binder, 100% AAS concrete was developed with four alkaline activators (NaOH, Na₂SiO₃, Na₂SO₄, and Na₂CO₃). Sodium sulfate (Na₂SO₄) at 5% by binder mass produced the highest 28-day compressive strength of 58.67 MPa—a 21.5% enhancement over the non-activated slag mix. NaOH- and Na₂SiO₃-activated systems exhibited superior durability, with only 4.1–5.7% strength loss after 90 days in 5% H₂SO₄ and durability factors exceeding 92% after 300 freeze–thaw cycles. The optimized Na₂SO₄-activated AAS concrete offers comparable or superior mechanical performance to OPC concrete while eliminating Portland cement and drastically reducing embodied CO₂ emissions, presenting a sustainable, high-performance alternative for structural applications.