Ceramics-Silikáty

To systematically evaluate the sulfate resistance of alkali-activated slag-based concrete (ASFC), this study investigates its mass variation, surface characteristics, compressive strength development, and evolution of sulfate erosion depth under dry-wet cyclic sulfate exposure. Furthermore, by analyzing the hydration products and microstructural morphology of ASFC, the failure mechanism under sulfate attack is elucidated. The results show that Sulfate wet-dry cycling saw all ASFC specimens’ mass rise, then drop, yet stay above the initial value. BSF specimens showed slightly surface damage (only fine cracks) than PSF ones (severe cracking and aggregate spalling); at fiber dosage ˂0.85%, BSF specimens had shallower damage depth than single SF/PSF ones, showing better sulfate resistance. PSF specimens had lower strength than SF, which caused agglomeration and a sharp decline in strength in late cycles. BSF specimens had marginally higher early strength than SF ones and far better strength retention, with superior mechanical performance. Sulfate attack produces expansive ettringite and gypsum in ASFC, inducing cracking and spalling via internal pressure. Hybrid fibers inhibit crack propagation to alleviate deterioration, and this effect is optimal when basalt fiber content is ≤0.55%, realizing the best crack and damage control under sulfate exposure. This study demonstrates that incorporating hybrid steel-basalt fibers into alkali-activated slag concrete at a basalt fiber dosage of 0.55% significantly enhances resistance to sulfate-induced degradation.