Durability of Steel Bridge Deck Paving Materials Under Salt Attack in Coastal Hot–Humid Environments

Steel bridge deck pavements in coastal hot–humid regions are often exposed to the combined effects of moisture, salt, and temperature, which can accelerate material deterioration and shorten service life. To clarify the durability behavior of typical paving materials under such conditions, a comparative study was conducted on three asphalt mixtures used for steel bridge deck pavements: epoxy asphalt mixture (EA-10), dense-graded asphalt mixture (AC-13), and stone mastic asphalt mixture (SMA-10). The mixtures were subjected to hygrothermal salt-water cycling using a mixed chloride-sulfate solution, and their durability was evaluated through air void content, indirect tensile strength, and four-point bending fatigue tests. The results showed varying degrees of deterioration. The air void content of AC-13 increased by about 41.4% after 28 d at 60 °C, suggesting greater susceptibility to internal void damage under severe conditioning. The indirect tensile strength also decreased with wet–dry cycling; at 60 °C and 28 d, the strength retention of EA-10 remained 76.9%, higher than those of AC-13 and SMA-10. After conditioning at 60 °C, the fitted slope of fatigue life for SMA-10 reached −0.0052, compared with −0.0044 for AC-13 and 0.0027 for EA-10, indicating that SMA-10 was the most sensitive to hygrothermal salt attack, whereas EA-10 was the least affected. Overall, the resistance to hygrothermal salt-water damage followed the order EA-10 > AC-13 > SMA-10. The findings help clarify the durability behavior of steel bridge deck paving materials in coastal environments and provide support for durability-oriented material selection.