Effect of sea sand on the corrosion resistance of steel bars in alkali-activated slag mortars: Correlation with hydration products

Alkali-activated slag sea sand mortar provides a sustainable alternative to ordinary portland cement by reducing carbon emissions and addressing the shortage of natural aggregates. However, the chloride ions in sea sand increase corrosion risks. This study assessed the mechanical properties, pH, chloride ion binding capacity, and steel bar corrosion in alkali-activated slag sea sand mortar. X-ray diffraction and thermogravimetry analyses showed the relationship between hydration products and corrosion. Steel bar corrosion was evaluated using corrosion potential, current density, and polarization resistance. At low sea sand replacement rates (≤30 %), the chloride ion binding capacity and pH of the mortar remain relatively stable. However, at higher sea sand replacement rates (≥50 %), the formation of C-(A)-S-H gels significantly decreases, while the generation of Friedel's salt increases. Despite this, the total production of Friedel's salt remains relatively low, while C-(A)-S-H gels are produced in greater amounts. As a result, chloride ions in the alkali-activated material (AAM) system are primarily bound through the physical adsorption of C-(A)-S-H gels. Consequently, as the sea sand content increases, the chloride ion binding capacity of the mortar decreases. Additionally, the higher sea sand replacement rate reduces pH, hindering steel bar passivation and accelerating corrosion. Two years of electrochemical measurements show that corrosion potential gradually increases and stabilizes with curing age. At higher sea sand replacement rates, corrosion potential decreases, current density increases, and polarization resistance drops. After 730 days, the mass loss of steel bars in the S1, S2, S3, and S5 groups was reduced by 52.45 %, 39.14 %, 33.18 %, and 22.73 %, respectively, compared to the OPC group. This study provides a theoretical basis for using sea sand in alkali-activated cementitious materials and insights for green building materials in marine engineering and resource-limited areas. • The combination of sea sand and alkali-activated materials was used. • Steel bars corrosion was characterized in alkali-activated sea sand slag mortar by electrochemical measurements. • The correlation between hydration products and the corrosion resistance of steel bars was investigated. • During the two-year monitoring, the steel bars' corrosion rate was lower under low sea sand content.