Coupled effects of different sulfuric acid concentrations and treatment methods on the corrosion rate of concrete materials

The durability of concrete structures in acidic environments has become an increasingly critical issue, particularly in applications such as wastewater treatment. Sulfuric acid attack is one of the most severe forms of concrete deterioration, with its rate influenced by both acid concentration and surface treatment methods. However, existing research has predominantly focused on individual factors, lacking a systematic analysis of their coupled effects. This study investigates the combined impact of three sulfuric acid concentrations (pH=2, 3, 4) and three surface treatment methods (A: no solution replacement or cleaning; B: solution replacement without cleaning; C: solution replacement with cleaning) on concrete corrosion through long-term immersion tests. By analyzing cumulative acid consumption, surface corrosion morphology, and microscopic characteristics of corrosion products, three typical corrosion types and their underlying mechanisms are identified. Under high acidity (pH=2) with frequent cleaning and solution replacement, the concrete is more prone to deep corrosion. As pH decreases, the degree of corrosion intensifies, with both corrosion rate and acid consumption increasing markedly. Based on corrosion product characteristics, the corrosion types can be classified into three categories: Type I forms a stable dihydrate gypsum layer that effectively inhibits corrosion; Type II generates silica flocculent products, with acid consumption increasing by 6.5 times per unit pH decrease; and Type III exhibits no protective layer, with acid consumption increasing by 8.0 times per unit pH decrease. This study elucidates the synergistic mechanism between sulfuric acid concentration and surface treatment, providing critical insights for the durability design and protection of concrete structures in extreme acidic environments.