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Fracture Mechanical Properties of Steel Fiber Reinforced Self-Compacting Concrete under Dry–Wet Cycle Sulfate Attack

Sulfate attack is the most common form of the durability damage of hydraulic concrete, and the performance degradation of cracked structural components is more significant at the position of water level change. Fly ash, a widely utilized supplementary cementitious material, can effectively improve the durability of concrete. In this paper, fly ash was used to partially replace Portland cement at 0 w%, 40 w%, 50 w%, 60 w%, and 70 w%, respectively. Through the three-point bending beam test with notch and the dry–wet cycle of sulfate attack, the change law of the fly ash content on the fracture mechanical properties of steel fiber reinforced self-compacting concrete (SFSCC) and its degradation mechanism under sulfate attack was studied. The results show that the load–crack mouth opening displacement curve of SFSCC changed from a steamed bread peak to a sharp peak under 30 dry–wet cycles of sulfate attack. The fracture toughness, peak load, and fracture energy of SFSCC with a high-volume fly ash increased with the increase in the fly ash content, while they reversed after sulfate attack. When the percentage of fly ash was 70 w%, the retention ratio of the fracture parameters was lower than that of SFSCC without incorporating fly ash, and when the percentage of fly ash was 50 w%, SFSCC had good bearing capacity, fracture mechanical properties, and corrosion resistance. The corrosion product of the reference SFSCC with 30 dry–wet cycles of sulfate attack was ettringite, whereas the SFSCC with a high-volume fly ash had no obvious corrosion products and the microstructure became looser.