Modelling of chloride penetration into non-saturated concrete: Case study application for real marine off shore structures

Abstract

The aim of this paper is to explain the chloride concentration profiles obtained experimentally from control
samples of an offshore platform after 25 years of service life. The platform is located 12 km off the
coast of the Brazilian province Rio Grande do Norte, in the north-east of Brazil. The samples were
extracted at different orientations and heights above mean sea level. A simple model based on Fick’s second
law is considered and compared with a finite element model which takes into account transport of
chloride ions by diffusion and convection. Results show that convective flows significantly affect the
studied chloride penetrations. The convection velocity is obtained by fitting the finite element solution
to the experimental data and seems to be directly proportional to the height above mean sea level and
also seems to depend on the orientation of the face of the platform. This work shows that considering
solely diffusion as transport mechanism does not allow a good prediction of the chloride profiles.
Accounting for capillary suction due to moisture gradients permits a better interpretation of the material’s
behaviour.