In this study, dried biomass of the alga Chlorella vulgaris was ground into a powder as an eco-friendly, low-cost inhibitor to mitigate the corrosion of carbon steel in acidic solutions. Electrochemical and weight loss measurements, surface morphology observations, adsorption isotherms, activation energy, and potential of zero charge calculations were applied to evaluate the inhibition performance. Electrochemical results indicate that C. vulgaris powder can simultaneously inhibit both the anodic and cathodic corrosion processes of carbon steel, demonstrating good inhibition performance and classifying it as a mixed-type inhibitor with both anodic and cathodic characteristics. Weight loss data further confirm that at a concentration of 300 mg/L, the corrosion inhibition efficiency reaches 88%. The fitted adsorption isotherm reveals that the adsorption of Chlorella vulgaris powder on the carbon steel surface follows the Langmuir model. Density functional theory (DFT) and molecular dynamics simulations indicate that the excellent inhibition performance is attributed to the combined effects of physisorption and chemisorption of constituents such as amino acids and cellulose present in C. vulgaris.

The durability deterioration of concrete under the coupled action of freeze–thaw cycles and corrosive media is a critical technical challenge for engineering structures in cold regions and salt corrosive environments. This paper systematically reviews the research progress on the mechanical properties of concrete subjected to coupled freeze–thaw and corrosion effects. Starting from the mechanisms of freeze–thaw damage and corrosion damage, it analyzes the material degradation laws under individual factors and the synergistic failure mechanism of the coupled freeze–thaw–corrosion condition. The coupling effect is revealed: freeze–thaw-induced microcracks accelerate the penetration of corrosive media, while the expansion of corrosion products in turn aggravates freeze–thaw damage. Building on this, from the perspective of factors influencing concrete failure, this paper systematically summarizes the key factors governing concrete damage under single-factor and coupled-factor conditions as well as their nonlinear response characteristics. The review indicates that the damage degree under the coupled action is far greater than the simple superposition of damage caused by individual factors and presents complex patterns, including the concentration threshold effect, the time-sequence effect, and sensitivity to a low water–cement ratio. Existing reviews predominantly focus on qualitative descriptions of single-factor deterioration mechanisms, while systematic comparative analyses of threshold behaviors under multi-factor coupling and quantitative consolidation of mechanical degradation metrics remain limited. Furthermore, targeted durability design guidance tailored to cold saline environments is rarely summarized in the prior literature, which motivates the present comprehensive review. Although existing studies are relatively well-established for single damage mechanisms, further efforts are still needed to deepen the understanding of multi-factor interaction thresholds and dynamic evolution processes. The findings of this review can provide theoretical support and engineering reference for the durability design and service life prediction of concrete structures in cold regions and salt corrosive environments. The summarized threshold laws and quantitative mechanical degradation data can provide targeted parameter guidance for the durability design of hydraulic structures, bridge substructures, and port engineering in northwest saline soil, northern severe cold, and eastern coastal salt fog areas.