As part of the maintenance policy of the dutch Ministry of Transport, Civil Engineering Division, hydrophobic treatment of concrete was considered as an additional protective measure against penetration of aggressive substances, for instance deicing salts in bridge decks. A set of tests was designed to determine the performance of commercial silicone-based products, using typical 'bridge' concrete (made with OPC or blast furnace slag cement). Nine products were tested; three complied to all requirements. Treated and non-treated concrete specimens were exposed to weekly salt ponding/drying cycles for 12 months. The amount of chloride that had penetrated the hydrophobic concrete was about 20% of that in the controls. © 1997 Elsevier Science Ltd.