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[Display omitted] • Influence of PCT and additives on the compressive strength and permeability was investigated. • Low strength ratios of permeable concrete to cement paste results from the low bonding area. • Enhanced bonding ratio can produce the greatest benefit in terms of strength. • Loss of permeability is the result of both reduced connected porosity and increased tortuosity. • Cement paste thickness distribution and pore size distribution were predicted by lognormal function. The macro performance and mesostructure of permeable concrete are largely determined by the paste coating thickness (PCT) on aggregates within the fresh mixture. Accordingly, in the present study, the strength and permeability of permeable concrete with different paste coating thicknesses were measured. The mesostructure characteristics of cement paste and pore were subsequently quantified by X-ray CT images and image processing techniques. As a result, the influence of PCT on the compressive strength and permeability, the characteristics of cement paste and pore was determined. The distribution of cement paste thickness and total pore size were used as functions of paste coating thickness, which coud be used to predict these mesostructure characteristics at the design stage of permeable concrete. The significance of this paper includes providing a deeper understanding of the relationship between macro performance and mesostructure from the perspective of paste coating thickness within mixtures. [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]

• The effect of seawater and sea sand at different stages of preparation on the performance of AWC mortar was systematically studied. • The adverse effect of seawater on the properties of AWC mortar at the molding stage was found for the first time. • The mechanism of the influence of seawater on AWC properties at the molding stage was revealed. Seawater and sea sand are widely used in marine concrete to overcome the shortage of freshwater and river sand. However, the effect of the various salts in seawater and sea sand on the performance of anti-washout underwater concrete (AWC) is unclear. In this study, the influence of seawater and sea sand, as well as the aggressive ions in seawater, on the anti-washout ability, mechanical performance, and microscopic structure of AWC mortar are studied systematically. The AWC mortar molded in seawater has a lower compressive strength even though its indicators of anti-washout ability perform better than that in freshwater. This is because Mg2+ in seawater chemically binds with OH– in cement to form Mg(OH) 2 film absorbed by anti-washout admixture(AWA), which inhibits the release of substances in AWC while also introducing more defects in AWC. This study lays the foundation for promoting the application of seawater and sea sand AWC in marine engineering. [ABSTRACT FROM AUTHOR]

The anti-washout concrete (AWC) made with seawater and sea sand has a limited marine infrastructure application due to its unfavorable properties. Our study proposes an effective performance enhancement method for AWC using silica fume. A comprehensive examination was carried out to investigate the effects of silica fume on AWC's flowability, anti-washout ability, compressive strength, microstructure, permeability, and abrasion resistance, with the AWC prepared with seawater and sea sand, and molded in seawater. It was discovered that 10 % silica fume can most effectively improve the performance of AWC. This enhancement is due to the pore structure refinement realized with C-S-H gel generated from pozzolanic reaction. Exceeding 10 % silica fume content can have a detrimental effect on the slump-flow of mixtures, while only providing marginal improvements in impermeability and compressive strength. The study lays a fundamental groundwork for the wide use of sea-based resources and the application of AWC in marine engineering. • The science behind modification of AWC mortar molded in seawater using silica fume was revealed. • The effects of silica fume on the performance of AWC molded in seawater were thoroughly explored. • The optimal content of silica fume to improve performance of AWC molded in seawater was identified. [ABSTRACT FROM AUTHOR]