A method to protect against corrosion of steel cables in a concrete member; wherein the cable to be protected comprises an array of wires arranged for providing reinforcement to said concrete member; wherein the array is a helical array of wires which are held together in a confined array with each wire butting against its neighbors and held in contact with its neighbors by the loads therebetween generated by tension on the cable; wherein one of the following applies: a) the concrete is intimately bonded to the cable and the cable is intimately surrounded by the concrete; or b) in a bonded post-tensioned concrete structure, there is a cementitious grout contained within a tubular container extending along the concrete member which is bonded intimately to the wires of the cable; or c) in an unbonded post-tensioned concrete structure, the cable is intimately surrounded by an extruded plastic sleeve extruded onto the cable and there is provided a non-bonding filler material in the external interstices between the cable and the plastic sleeve arranged to allow sliding of the cable within the plastic sleeve during tensioning; wherein when a) or b) applies, the concrete or the cementitious grout is engaged with and intimately bonded to a periphery of the cable so that there are insufficient interconnected spaces between the cable and the concrete or cementitious grout to allow passage of fluid along the cable between the cable and the concrete or cementitious grout; wherein when c) applies, the non-bonding filler material in the plastic sleeve engages a periphery of the cable so that there are insufficient interconnected spaces between the cable and the plastic sleeve to allow passage of fluid along the cable between the cable and the plastic sleeve; and wherein the method comprises the steps of: exposing the wires of the array at a first location in said concrete member, either at an end of the array or at a side face of the array spaced from the end; and protecting the steel cable against corrosion by: inserting a fluid directly into interstitial spaces between the wires of the cable at said first location along the cable for travel to a second location along the cable; and providing a pressure differential in the fluid between the first and second locations to cause the fluid to pass through the interstitial spaces between the wires of the cable. a) the concrete is intimately bonded to the cable and the cable is intimately surrounded by the concrete; or b) in a bonded post-tensioned concrete structure, there is a cementitious grout contained within a tubular container extending along the concrete member which is bonded intimately to the wires of the cable; or c) in an unbonded post-tensioned concrete structure, the cable is intimately surrounded by an extruded plastic sleeve extruded onto the cable and there is provided a non-bonding filler material in the external interstices between the cable and the plastic sleeve arranged to allow sliding of the cable within the plastic sleeve during tensioning; exposing the wires of the array at a first location in said concrete member, either at an end of the array or at a side face of the array spaced from the end; and protecting the steel cable against corrosion by: inserting a fluid directly into interstitial spaces between the wires of the cable at said first location along the cable for travel to a second location along the cable; and providing a pressure differential in the fluid between the first and second locations to cause the fluid to pass through the interstitial spaces between the wires of the cable. inserting a fluid directly into interstitial spaces between the wires of the cable at said first location along the cable for travel to a second location along the cable; and providing a pressure differential in the fluid between the first and second locations to cause the fluid to pass through the interstitial spaces between the wires of the cable.