Leaching of concrete : the leaching process and its effects

Abstract: The present report presents an experimental study of leaching of concrete caused by water percolating through the concrete, or by diffusion from concrete to external water in contact. An apparatus was designed and constructed in which de-ionised water could be forced, by external pressure, through a number of concrete specimens of differing characteristics. It was found that, whereas the initial water flow was normally low and uniform, most specimens showed a rapid increase in water flow after a certain period of time. This was probably due to formation of certain distinct percolation channels. The solid material around these channels was leached, the concrete becoming disintegrated, and almost no continuous cementitious material being left to maintain strength and tightness of the concrete. The chemical composition of the percolated water was analysed, making it possible to calculate the amount of leaching and consequently to theoretically assess the increase in porosity and reduction of strength Changes in the structure of concrete caused by leaching were also investigated experimentally by measurements of porosity, pore size distribution and strength. ESEM-EDX-studies were made in order to find out the morphology of leached concrete. Results from all these experimental studies are presented in the report. A theoretical model of the leaching process and its effects on the material and on the structural stability of real structures was developed. The model is applied to the experimental data.