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

The effect of nano-silica, nano-alumina and binary combinations on surface hardness, resistance to abrasion and freeze-thaw cycle resistance in cement mortars was investigated. The Vickers hardness, the Los Angeles coefficient (LA) and the loss of mass in each of the freeze–thaw cycles to which the samples were subjected were measured. Four cement mortars CEM I 52.5R were prepared, one as control, and the other three with the additions: 5% nano-Si, 5% nano-Al and mix 2.5% n-Si and 2.5% n-Al. Mortars were tested at 7, 28 and 90 d of curing to determine compression strength, total porosity and pore distribution by mercury intrusion porosimetry (MIP) and the relationship between the CSH gel and Portlandite total by thermal gravimetric analysis (TGA). The capillary suction coefficient and an analysis by a scanning electron microscope (SEM) was made. There was a large increase in Vickers surface hardness for 5% n-Si mortar and a slight increase in resistance to abrasion. No significant difference was found between the mortars with nano-particles, whose LA was about 10.8, classifying them as materials with good resistance to abrasion. The microstructure shows that the addition of n-Si in mortars refines their porous matrix, increases the amount of hydrated gels and generates significant changes in both Portlandite and Ettringite. This produced a significant improvement in freeze–thaw cycle resistance. The effect of n-Al on mortar was null or negative with respect to freeze–thaw cycle resistance