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Despite extensive academic research on durability issues caused by sulfate attack, deterioration reasons and expansion mechanisms of concrete remain controversial, with descriptions of expansion development still focusing on phenomenological observations. The present study analyzes the macro-micro property changes of concrete and establishes a time-varying expansion prediction model considering environmental and material parameters. The micropore evolution in different pore categories is investigated, and the primary type and precipitation location of expansive products, as well as the expansion mechanism of concrete, are clarified. The results indicate the possibility of thaumasite sulfate attack (TSA) in concrete at low temperatures. The expansion development of concrete under sulfate attack can be divided into two stages: the expansion latency stage explained by crystallization pressure theory, and the significant expansion stage associated with volume increase theory. The expansion level at the inflection point of the expansion rate was solely related to the intrinsic micropore properties of concrete. • The relationship between macroscopic performance changes and micropore evolution was revealed. • A time-varying prediction model for concrete expansion development under sulfate attack was established. • The precipitation location of products and the expansion mechanism were clarified. [ABSTRACT FROM AUTHOR]

Assessing the long-term durability of concrete structures subjected to external sulfate attack (ESA) poses a significant challenge, primarily due to the lack of a well-defined quantitative metric for durability limit states. Traditional performance indicators such as compressive strength, mass loss, and expansion strain are insufficient for providing a comprehensive understanding of the extent of damage and are often difficult to measure accurately in practice. The primary objective of this study is to introduce a novel durability failure indicator, namely the failure thickness of concrete under ESA exposure, designed to quantitatively assess the ultimate limit state of concrete durability. Experiments were conducted and the results confirmed that the failure thickness can reliably reflect changes in both the elastic modulus and compressive strength of concrete exposed to ESA. A prediction model for estimating the failure thickness was subsequently developed, integrating key influencing factors like sulfate concentration, initial aluminate content, and sulfate ion diffusion coefficient. The established model exhibited a high degree of correlation between the predicted and experimental failure thickness values, with a low margin of error. The findings of this research contribute to serve as a foundation for both lifespan prediction and durability design of concrete structures exposed to sulfate-rich environments. • We propose a durability failure indicator based on critical sulfate concentration. • Concrete performance deterioration can be well characterized by failure thickness. • The validity of the prediction model of failure thickness was confirmed. [ABSTRACT FROM AUTHOR]