Under the marine environment, the main cause of degradation of reinforced concrete structure is the corrosion of steel bars. It is due to the presence of chloride ions into the concrete porosity. When the chloride ions concentration reaches a critical value, steel bars are not protected and corrosion can start. This work studies the chloride propagation within a coasting concrete structure. This structure is a quay of the Nantes Saint-Nazaire harbour (P.A.N.S.N.) located in the estuary on the West Atlantic coast and built in 1971. In situ measurements of chloride profiles are realised for longitudinal and transversal beams and for slab in different locations and different orientations (north, south, east, west and under face). These profiles are determined by a destructive method using at the end the titration of chloride solution. The diffusion coefficients are calculated by using the Fick’s law and they permit to quantify the concrete quality in relationship with the location. A statistical distribution of these data was carried out in the aim to predict the service life of the structure by using a probabilistic model. A second part deals with the chloride kinetics in this structure which is not always immersed. The kinetics propagation is also compared with two models existing in the literature. This approach will be compared later to experimental tests realised in laboratory and will allow the development of an empirical chloride propagation law in this quay structure. This will be done also with other structures because this work is done in the frame of a European Interreg III B project called Medachs.