Multiscale damage mechanisms of limestone under acid, alkali, and cyclic conditions

Abstract Chemical corrosion is a critical factor driving the degradation of rock engineering properties, particularly in carbonate-rich formations. To investigate the mechanisms of limestone deterioration under extreme chemical conditions, this study conducted continuous immersion tests in acidic (pH = 2, H₂SO₄) and alkaline (pH = 12, NaOH) solutions, together with wet–dry cycling and acid–alkali alternation experiments. A control group without chemical treatment was also included for comparison. The macroscopic and microscopic responses of limestone were systematically analyzed through porosity, mass loss, P-wave velocity, uniaxial compressive strength, and microstructural characterization. Results revealed that degradation severity followed the order: acid–alkali alternation > acidic wet–dry cycling > continuous acid immersion > alkaline ≈ control. After 30 days, the acid–alkali alternation group exhibited the most severe deterioration, with porosity increasing from 0.29% to 0.42%, mass loss reaching 0.92%, P-wave velocity decreasing from 5796 m/s (10 days) to 5268 m/s (30 days), and UCS declining from 43.83 MPa (10 days) to 33.73 MPa (30 days). At the microscale, acidic conditions promoted CaCO 3 dissolution with CaSO₄ precipitation (up to 11.6% during wet–dry cycles), enlarging pores and pore throats, while acid–alkali alternation triggered cyclic precipitation–dissolution stresses that produced interconnected microcrack networks. In contrast, alkaline conditions showed only weak passivation and precipitation. A strength prediction model was established based on the chemical damage variable D defined by P-wave velocity, which exhibited a strong power-law relationship with strength (R 2 ≈ 0.93). This study explains three coupled mechanisms—dissolution-dominated, dissolution–crystallization synergy, and chemical fatigue—and proposes a simple, economical, and non-destructive velocity–strength framework for rapid durability assessment and early warning in acid rain, industrial effluent, and underground engineering contexts.