7. Simple non-destructive test method for assessing surface layer permeability of concrete structures

Checking the surface permeability of concrete in structures to prevent water or salt infiltration after work has been carried out is important to guarantee their longevity. However, since there are no simple ways to inspect the permeability of concrete structures in-situ, present day quality management and inspection of the type of concrete used in structures rely primarily on strength tests and material composition. There have been cases however, where even though a type of concrete passed strength and material composition tests, its permeability in-situ was defective, leading to early corrosion of rebars etc. This concern led to urgent calls for a non-destructive test method which could be used to verify the permeability of concrete actually used in structures.

Consequently a proposal was made for a simple non-destructive test method which could be applied by a single person and did not require a direct power supply. The method in question comprises a small spray canister and a battery operated device to measure surface colour change (Fig.1).

Concrete with integrity dense structure does not immediately absorb water. Its surface will very quickly become saturated with repeated spraying of small quantities of water. The present method therefore measures the speed of surface discoloration in order to determine the level of saturation. Tests demonstrated that this method was an effective means to easily determine the state of permeability of the concrete by finding the relationship between the saturation value and number of spray applications (Fig.2).

The method was found to be suited to the stated purpose, and to be easily adaptable to the required working environment. Its simplicity means that it can be used for multiple testing during a single visit, making it viable as a preliminary screening test. It is hoped that it will contribute to improving the quality of concrete used on structures.