Abstract: To analyze the influence of sustained axial compression loads and wet-dry cycles on the sulfate erosion resistance of cement mortar, a combination of macroscopic and microscopic experiments was conducted. We compared the appearance phenomena, appearance quality, expansion rate, and strength degradation characteristics of the cement mortar under different conditions aiming to explore the erosion mechanisms involved. The results revealed that both sustained axial compression loads and wet-dry cycles significantly exacerbated the deterioration of mortar, with a more notable effect observed at higher stress levels. The mortar subjected to a stress ratio of 0.4 exhibited the highest increase in linear expansion rate, reaching 0.67%, and experienced the greatest loss in compressive strength, with a reduction of 40.72%. Under dry-wet cycles, the mortar displayed a maximum increase in linear expansion rate of 0.43% and a significant loss in compressive strength of 29.63%. Lower sustained axial compression loads initially mitigated sulfate erosion in the early stages but aggravated it later on. Conversely, higher sustained axial compression loads directly increased internal defects within the mortar, intensifying chemical erosion and leading to a substantial decline in macroscopic performance. The combined effect of wet-dry cycles and sulfate crystallization, calcium aluminate, gypsum, and other corrosion products contributed to the deterioration of the mortar's microstructure and the expansion of defects. Although the erosion mechanism of sulfates remained unaffected by sustained axial compression loads, these loads significantly influenced the erosion process. The degradation pattern of sulfate-resistant compressive strength in mortar can be effectively described by a binomial function. The research findings provide valuable guidance and support for the durability evaluation and the design of protective layers in hydraulic structures.

Key words: cement mortar, sulfate attack, continuous axial loading, dry-wet cycle, durability