Laboratory Assessment of Microstructural and Strength Evolution in Stylolite and Burrow Limestones Under Cyclic Wetting-Drying Conditions

Understanding the degradation behavior of carbonate rocks under cyclic climatic conditions is essential for predicting their long-term durability, particularly in coastal and arid environments. This study examines the evolution of the mechanical, chemical, and microstructural properties of stylolite and burrow limestone samples from Riyadh, Saudi Arabia. The rock samples were subjected to 15 wetting-drying (WD) cycles. A combination of destructive and non-destructive tests, including computed tomography (CT) scanning, ultrasonic wave velocity analysis, unconfined compression strength (UCS), porosity measurements, and chemical composition mapping, was conducted. The results reveal differential degradation patterns linked to initial heterogeneity. Stylolite samples exhibited a nonmonotonic trend in UCS, with a peak strength loss of approximately 50% of the original strength at the 5 th cycle, followed by partial recovery. Burrow samples demonstrated a 27% gradual reduction in UCS. CT revealed concentrated pore structure degradation in stylolites at the mid-height of the sample, with severe effects observed at the 5 th and 15 th cycles. In contrast, the burrow samples experienced uniform degradation with the progression of WD. Despite the constant water absorption with WD cycles, the porosities of all the samples progressively increased. X-ray fluorescence mapping confirmed a progressive loss of calcium, accompanied by the simultaneous evolution of silicates and chlorides, particularly in burrow samples, suggesting that chemical alteration is a degradation mechanism. The wave velocity results correlated with microstructural damage revealed greater reductions in stylolite samples than in burrow samples. These findings emphasize the importance of considering rock fabrics, chemical stability, and microstructural evolution in the engineering design of special projects exposed to cyclic moisture fluctuations. • Stylolite limestone lost half of its strength at 5th wet-dry cycle, suggesting early vulnerability and potential for partial recovery which is critical for short-term performance. • CT scans showed localized damage in stylolite and uniform degradation in burrow limestone, emphasizing the role of rock fabric in durability. • Both increased porosity and reduced wave velocity, particularly in stylolite, aligned with internal damage which is useful for durability assessment. • Salt crystallization established through chemical mapping directly relates to pore structure densification observed in CT scan.