Abstract
Owing to its importance in the assessment of reinforced concrete structures, it is essential to determine the chloride diffusivity of fly ash concrete. This paper presents an investigation into the diffusion characteristics of chloride ions in fly ash concrete. Through experiment, the relationship between chloride diffusivity and curing age up to 1800 days is measured and the effects of curing age, water/binder ratio, aggregate volume fraction, and fly ash content (i.e., percentage of total cementitious material by mass) on chloride diffusivity are evaluated. It is found that the chloride diffusivity decreases with the increase of curing age, aggregate volume fraction, and fly ash content, but increases with the increase of water/binder ratio. In analytical modeling, an equivalent aggregate model is constructed and the equivalent interfacial transition zone (ITZ) thickness is derived analytically. With the equivalent aggregate model, three-phase fly ash concrete reduces to a two-phase composite material. By extending the Maxwell method, the chloride diffusivity of fly ash concrete is formulated. Finally, the validity of the analytical method is verified by experimental results.
Highlights
Reinforced concrete structures may be subjected to reinforcement corrosion when they are built in a harsh environment
To improve the durability of reinforced concrete structures, fly ash is often added into concrete as a mineral admixture, and the chloride diffusivity can be reduced significantly owing to the pozzolanic reaction of fly ash [3,4]
Poon et al [5] demonstrated by a mercury-injection method that mixing fly ash into mortar and net cement paste can greatly reduce the porosity of the interfacial transition zone (ITZ) and the cement paste matrix
Summary
Reinforced concrete structures may be subjected to reinforcement corrosion when they are built in a harsh environment. It has been shown that the pozzolanic reaction of fly ash occurs mainly in later curing ages from 90 to 360 days [5,6,7] Such hydration characteristics can reduce the porosity and improve the pore structure of concrete for a long time [8,9], making concrete increasingly denser and improving the penetration resistance against chloride ions. Yu and Ye [14] further studied experimentally the influence of curing age on the diffusion of chloride ions in fly ash concrete. They found from mercury intrusion porosimetry (MIP) tests that the microstructure is continuously improved during the curing period and fly ash still plays a part in enhancing the penetration resistance against chloride ions within a long duration. The validity of the analytical method is verified with experimental results
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