Abstract: To address the durability challenges faced by concrete linings in highway tunnels in the salt-containing geological environment of Chuxiong Prefecture, Yunnan Province, China, the authors investigate the influence of fly ash on the resistance of concrete to sulfate erosion. Experimental methods coupling dry-wet cycles with sulfate erosion are employed. The deterioration mechanism is analyzed based on the surface morphology and mass loss rate of concrete. Additionally, a concrete erosion damage model based on the Weibull function is established and compared with experimental results. The results indicate the following: (1) In the initial stages of erosion, ettringite and gypsum fill the voids, leading to an increase in specimen mass. (2) In the later stages of erosion, when the expansion stress of erosion products exceeds the internal stress of the concrete structure, cracks appear and propagate, resulting in severe damage to the concrete and a decrease in specimen mass. The addition of an appropriate amount of fly ash enhances the anticorrosion grade of concrete, with the most optimal improvement observed when 20% fly ash is added. However, when fly ash is added excessively (25%), the anticorrosion grade of concrete decreases. (3) The predictive model for anticorrosion grade based on the Weibull distribution function using the erosion coefficient as damage severity effectively reflects the degradation pattern of fly ash concrete under erosion. The correlation coefficients R² of all model sets are above 0.95, with prediction errors relative to experimental data within 15%, indicating high precision.

Key words: tunnel, fly ash concrete, dry-wet cycle, sulfate erosion, durability, Weibull distribution, anticorrosion grade