Mechanochemical Treatment of Low-Alkali Activated Slag Concrete: A Comparative Study of Potassium and Sodium Activators

This study investigates the impact of mechanochemical treatment (MT) on alkali-activated slag concrete (AC), comparing the performance of sodium-based (M-NAC) and potassium-based (M-KAC) systems. Ground granulated blast furnace slag (GGBS) was used as an aluminosilicate source, activated with alkali silicates and hydroxides, and subjected to mechanochemical treatment in a planetary ball mill to enhance precursor reactivity by significantly reducing particle size and increasing surface area. The treated precursors were mixed with fine and coarse aggregates and alkali solutions to produce AC. The study assessed mechanical properties of AC at low (2 M) and high (10 M) concentrations of alkali such as compressive, flexural, and splitting tensile strength and durability properties, including water absorption, permeability, ultrasonic pulse velocity, rapid chloride permeability, and acid resistance, along with microstructural analysis using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Results showed that mechanochemical treatment greatly improved the performance of AC at low dosages of alkali by increasing the amorphousness and reactivity of the GGBS precursor. M-KAC consistently outperformed M-NAC, demonstrating superior long-term strength gains of over 5%, reduced permeable voids by more than 7.5%, and decreased water absorption by over 3%. Microstructural analysis revealed the formation of a dense KASH gel in M-KAC, contributing to its enhanced durability, lower chloride ion penetration, and greater resistance to acidic environments. Compared with sodium-based systems, M-KAC exhibited up to 40% lower chloride permeability and superior acid resistance, confirming its suitability for use in harsh conditions. These findings highlight the significant potential of M-KAC for sustainable construction, emphasizing the role of mechanochemical treatment in improving the performance of AC by lowering the alkali dosage. The research demonstrates the effectiveness of potassium-based AC as an eco-friendly, high-performance alternative to conventional cement, offering a viable pathway to reducing carbon emissions and enhancing the durability of concrete structures in aggressive environments.