Deterioration mechanism and service life prediction of concrete under the coupled action of scouring, sulfate attack and wet-dry cycles

Hydraulic concrete structures have long been facing severe multi-factor coupling challenges from water scouring, sulfate attack, and wet-dry cycles, and their accelerated performance deterioration severely limits the engineering service life. To reveal the damage mechanism, this study conducted wet-dry cycle tests considering water scouring speeds (0, 600, 1200 r/min) and different environmental erosion effects (clean water, 5% Na₂SO₄ solution). The evolution laws of concrete mass loss rate, compressive strength, and relative dynamic elastic modulus were systematically investigated, while scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) were employed to reveal the microstructural morphology and phase evolution process of hydraulic concrete. The results show that in the early stage of corrosion, sulfate attack products continuously fill the pores, and the concrete strength gradually increases. With the increase of corrosion cycles, physical scouring, chemical attack, and wet-dry transport exhibit strong synergistic effects. Surface scouring accelerates the transport of sulfate ions, and the excessive accumulation of attack products induces expansion stress, which leads to pore structure damage and microcrack propagation. Consequently, a vicious cycle of "abrasion-invasion-expansion-cracking" is formed, and the concrete performance deteriorates sharply. The service life prediction model of hydraulic concrete established based on the macroscopic performance degradation law and the Birnbaum-Saunders (B-S) distribution indicates that in a 5% sulfate environment, with the increase of scouring speed, the service life of hydraulic concrete continuously decreases, and the predicted service life is shortened by nearly 25%. This study provides key theoretical support for the durability design and life assessment of hydraulic concrete in harsh environments.