Electrolytic protection of steel-reinforced concrete bodies such as bridges and building facades is achieved with carbon material inserted into the concrete body. The carbon material is connected to act as a anode with the steel reinforcement as a cathode, so that corrosive chloride ions migrate away from the steel reinforcement. The carbon material is inserted so as also to act as a reinforcement. In one arrangement carbon textile material is provided between inner and outer grout-filled plastics ducts fixed around post-tensioned steel cables. In another arrangement a carbon rod, or pin, is fixed between a concrete body and a steel I-beam.