Time variation law of chlorine diffusion coefficient of marine concrete structures in tidal zone and its influence on service life

Abstract

Chloride diffusion coefficient (Da) is an important parameter to predict chloride ion concentration in concrete, which is of great significance to the study of durability and service life of concrete structures in the Marine environment. The alternating wet and dry environment in tidal zone has a significant impact on the deterioration of concrete's chloride ion erosion resistance. It is extremely important to study the chloride ion diffusion coefficient in the tidal zone. In this paper, the apparent chloride diffusion coefficient (Da) and its time-dependent constant (m) of concrete were calculated on the basis of a large number of natural exposure test data and engineering data in tidal zone at home and abroad, the time-varying law of chloride diffusion coefficient of marine concrete structures in tidal zone were discussed. The ChaDuraLife Model, DuraCrete model and Life-365 model were utilized to calculate the service life of concrete structures based on the immersed tube tunnel in the north Marine environment of China. The results showed that Da in tidal zone decreases with exposure time and presents a power function relationship. It was found that proper addition of mineral admixtures could improve the chloride ion erosion resistance of concrete structures in tidal zone during long-term service by reducing the chloride ion diffusion coefficient. The type of mineral admixture and the value of m would affect the calculation result of the service life of concrete structures. The addition of mineral admixture would lead to the increase of m, thus prolonging the service life of concrete structures. Service life calculated by different models was changed. The value of m of DuraCrete model was larger, so the calculated service life was longer. Similarly, the calculated service life of Life-365 model was shorter. It was noted that the ChaDuraLife Model was the most economical and safe model to predict the service life of concrete structures.