Acid Dissolution-Induced Damage Mechanisms in Concrete–Rock Composites: Experimental and Particle Flow Simulation

Concrete-rock composites (CRC) in karst regions face severe durability challenges from acid dissolution. This study investigates the damage mechanisms of CRC under sulfuric acid solutions (pH 3, 5, and 7) through integrated laboratory experiments and interface-enhanced discrete element modeling. The results reveal that chemical degradation occurs via H⁺-mineral reactions (e.g., CaCO₃ + H₂SO₄ → CaSO₄ + CO₂), increasing porosity by 14% at pH = 3 and reducing compressive strength by 28.5% compared to neutral conditions. Meanwhile, mechanical deterioration exhibits pH dependency: elastic modulus declines by 24.2% (pH 5) and 41.6% (pH 3), while failure transitions from concrete-dominated cracking (pH 7) to synergistic concrete-rock failure (pH ≤ 5). Moreover, PFC^2D simulations demonstrate that crack initiation consistently originates at the concrete-rock interface, with tensile cracks comprising >90% of total cracks. Stronger acidity increases total crack density by 10.7% (pH = 5) and 20.8% (pH = 3) and homogenizes crack angular distribution. These results establish a quantitative corrosion-degradation relationship, providing critical guidance for enhancing the durability of tunnels and bridges in acidic environments.