Determination of chloride ion diffusion coefficient in outer layer of concrete with silicate-type surface penetrant

摘要

Surface penetrants are often employed as part of preventive maintenance procedures for concrete structures. Guidelines for the use of surface penetrants state that chloride ingress into the reformed surface parts is different from that into the deeper, nonreformed parts; to ensure durability after repair, the design of the structure should consider the chloride ion diffusion coefficients of both the parts. However, there is no established method to determine the diffusion coefficient of the reformed part. This paper proposes a method for determining the apparent chloride ion diffusion coefficient in outer concrete layers reformed by silicate-type surface penetrants. The extent of surface penetration was investigated on the basis of the Vickers hardness distribution inside the concrete. Subsequently, a concrete specimen to which a surface penetrant was applied was exposed to a chloride environment, and the chloride ion concentration distribution in the concrete was measured. Simultaneously, the chloride ion distribution was measured for a concrete specimen without the penetrant treatment, and the two specimens were compared. To determine the diffusion coefficient of the penetrated part, a comparison was made by considering the equivalent cover depth. Such measurements imply that a segmented thickness with a low diffusion coefficient (conferred by the surface penetrant) can be replaced with a cover depth of normal concrete. The results showed that the penetration depths of the surface penetrants were 3-7 mm, and the apparent chloride ion diffusion coefficient was 0.4-0.6 cm~2/year. The applicability of the results was demonstrated by gauging the effect of the surface penetrant in delaying the onset of corrosion by using the apparent chloride ion diffusion coefficients calculated in the study. The results confirmed that the use of surface penetrants delays the initial stages of corrosion by up to a maximum of 18 years.