Q: Does copper corrode when it's embedded in concrete? I've heard that copper pipes that penetrate concrete floors and copper shower pans in contact with concrete or cement board can corrode. I've also been told to wrap protruding copper pipes with tar paper before embedding them in concrete.
A: According to petrographer Bernie Erlin, copper won't corrode in concrete unless soluble chlorides are present. When copper is adjacent to steel reinforcement, and an electrolyte such as chloride is present, steel corrosion is likely to occur due to galvanic action. Under these circumstances, you should insulate the copper with a suitable coating. Erlin also says that very small amounts of ammonia and possibly nitrates can cause stress corrosion cracking of copper pipes embedded in concrete.
Bernard Erlin, "Embedded Metals and Materials Other Than Reinforcing Steel," Significance of Tests and Properties of Concrete and Concrete-Making Materials, STP 169C, ASTM, West Conshohocken, Pa., 1994, pp. 176-177