Diffusion Experiment Of Chloride Ions In Concrete And Analysis Of Influential Factors

This thesis summarizes the important significance of durability of concrete structures and two kinds of durability design of concrete. The effects of chloride ion penetration on the durability of concrete structures and the penetration mechanism are mainly introduced and the theoretical background and testing methods of the anti-chloride penetration of concrete are discussed. The long-term immersion, dry-wet cycling and alternating-current resistance are selected as the testing methods in this thesis. Based on the practical environment in Zhejiang coastal areas, the dry-wet cycling period is designed. Applying the above testing methods, the effects of the water/binder ratio, contents of fly ash and FMA-H, maximum aggregate diameter, aggregate gradation and exposure environment on the diffusivity of concrete are analysed. A mixed anti-corrosion coating system is chosen to test the anti-chloride penetration of concrete.Based on the experimental results, it is shown that dry-wet cycling has a negligible influence on the chloride diffusivity of concrete and that the chloride concentration in dry-wet cycling is always larger than that in natural cycling. The chloride diffusivity of concrete decreases with the decrease of the water-binder ratio, the addition of mineral admixtures, the maximum aggregate diameter, the number of dry-wet cycles. It is also found that the chloride diffusivity of concrete with equal volume fraction gradation is obviously larger than that with Full gradation and that the chloride diffusivity of concrete in the splash zone is larger than that in the submerged zone.The electrical conductivity of normal concrete correlates well with its strength. The chloride diffusivity also correlates well with the electrical conductivity, with correlation coefficients of 0.8104 and 0.7608 for two types of concrete, respectively. The experimental results obtained from the alternating-current resistance method are obviously smaller than that obtained from the dry-wet cycling method. The fly ash concrete with surface coating is of the best anti-chloride penetration performance.In this thesis, the "critical penetration depth" is proposed to evaluate the anti-chloride penetration performance of concrete. It is found that the electrical conductivity of concrete is correlated with the critical penetration depth. The correlation increases with the increase of the number of dry-wet cycles and will be as large as 0.9326.