Progressive degradation and performance deterioration mechanisms of the limestone-concrete interface under combined sulfate attack and dry-wet cycles

To investigate the mechanical properties and degradation mechanisms of limestone-concrete interfaces under combined sulfate attack and dry-wet cycles, this study systematically examines the failure modes, pore structure evolution, and microstructural characteristics of composite specimens through an integrated approach incorporating compression-shear tests, digital image correlation (DIC), acoustic emission (AE) monitoring, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results demonstrate that the limestone-concrete interface serves as the critical zone for performance deterioration. Under compression-shear loading, crack initiation first occurs at the interface, followed by progressive propagation into the concrete matrix, ultimately forming an interconnected crack network that leads to brittle failure of the concrete. In contrast, the limestone exhibits superior durability, manifesting only superficial spalling while maintaining structural integrity. The peak compression-shear load displays a characteristic trend of initial increase followed by decrease with increasing dry-wet cycles. During the early stage (0–15 cycles), sulfate-induced reaction products effectively fill concrete pores, enhancing material compactness. Beyond 15 cycles, however, crystallization pressure during drying becomes dominant, causing crack coalescence and pore expansion that significantly degrade mechanical performance. MIP analysis reveals distinct pore structure evolution: micropores (< 200 nm) decrease during early cycles while macropores (> 200 nm) increase markedly in later cycles, demonstrating the competing effects of pore-filling and crystallization-induced damage. SEM observations further confirm initial microstructural densification followed by extensive crack network development and surface deterioration in advanced stages. AE parameters quantitatively characterize the dynamic transition of damage modes, revealing a dual-phase failure mechanism involving “pore-filling enhancement” followed by “crystallization-induced damage”. The study concludes that interface degradation under coupled sulfate attack and dry-wet cycling represents the controlling factor governing the mechanical performance and durability of limestone-concrete composite structures. Practical implications include the recommendation for optimized interface protection and erosion-resistant measures in engineering design to mitigate degradation and extend service life.