The installation and use of embedded sacrificial anodes to protect reinforced concrete may be improved. In one example a cavity [2] is formed in the concrete [3] and a puttylike backfill [4] is placed in the cavity and a compact discrete anode comprising a sacrificial metal element [1] is inserted into the backfill and a space is provided into which the backfill may move when subjected to a pressure arising from the formation of voluminous sacrificial metal corrosion products and a high current is passed from the anode to the steel in the concrete to arrest steel corrosion and activate the anode in the backfill. The space may be provided by venting the backfill to space outside the cavity through an opening [5] or by including a void space within the backfill [6] or a void space within the cavity [7].