Effects of different activators on corrosion resistance of alkali-activated slag binder in CO2-rich water

Abstract

To address critical challenge of structural durability of alkali-activated slag (AAS) cementitious materials exposed to CO₂-rich karst groundwater, a novel ternary composite activator (Na₂SO₄-Na₂O·1.5SiO₂-NaOH) was developed and its effectiveness was evaluated through comprehensive analysis of corrosion kinetics (mass variation, mechanical degradation, carbonation front progression) and multiscale microstructural evolution during prolonged corrosion ages. Results showed that the AAS under CO₂-rich water progresses through three distinct stages: (1) Leaching of Na⁺ and OH⁻;(2) Interlayer Ca²⁺ leaching from C-A-S-H gels and formation of CaCO₃; (3) Intralayer Ca²⁺ leaching from C-A-S-H gels and dissolution of CaCO₃. The ternary composite activator synergistically enhances durability by triple action. At first, Na₂O·1.5SiO₂ promotes the formation of dense C-A-S-H gels through the release of (SiO₄)^4-. And NaOH can stabilizes pore solution pH to inhibit acidification. In addition, Na₂SO₄ can refine pore structure while generating stable hydrotalcite and calcium sulfate phases. Optimal Na₂SO₄ content (20 %–40 % in Na₂O·1.5SiO₂ -based AAS; 30 %–50 % in NaOH-based AAS) reduces mass loss by 25 %–35 % and strength loss by 20 %–30 % compared to single activator. This work provides a novel strategy for designing low-carbon cementitious materials with superior resistance to aggressive karst groundwater.