The durability and aesthetic appearance of concrete may be improved by the addition of hydrophobizing agents as a consequence of reduced water permeability. Hydrophobizing agents lead to less water absorption at the same time as they let water vapour out. This may lead to a dryer interior over time and thereby reduced rate of detrimental reactions needing liquid water as reaction medium. The ingress of water born aggressives like chlorides will be reduced (in particular in marine splash zones), but also corrosion rates may be decreased. Carbonation rates may, however, be somewhat increased. Vegetable oils seem to be the most cost-effective hydrophobizing agents as good effects may be achieved by additions of only 0.5 % of the cement mass. Furthermore, the cheapest and most available vegetable oil based on rapeseed is among the most effective tested. It is recommende to continue research on the effect of rapeseed oil as a concrete admixture, also at dosages above 1.5 %. The research should focus on rapeseed oil as hydrophobizing agent, but also on its effect on other interesting concrete properties for COIN; like hardening retarder, shrinkage reducing agents, electrical resistivity and pH reduction
