Should reinforcing steel be cleaned of rust before use?
Not necessarily. Light coatings of rust or mill scale tightly bonded to the concrete do not cause trouble. Something must be done, however, if the rust is loose, or flaking and scaling enough to affect bond. Rust can be removed by scraping, wire brushing or sandblasting and sometimes by dropping, hammering or vibrating. It is not always necessary to get down to the bare metal. Bars that are rusted badly enough so that their size is below the tolerance allowed for new bars should not, of course, be used. An easy way to check is by weighing a measured length of bar from which the rust has been removed.