Repair of damaged structural concrete members is an art as well as a science for both contractor and engineer. The engineer must adapt the various available repair techniques available to him and coordinate them with field conditions so that the contractor's final repair is aesthetically acceptable, structurally sound, and does not interfere with operations of the facility. TYPES OF REHABILITATION There are five basic types of structural strengthening that can be considered without resorting to completely demolishing and rebuilding the member or systems of members. These strengthening techniques are: internal restoration; exterior reinforcement; exterior post-tensioning; jackets and collars; and supplemental members. INTERNAL RESTORATION The most common way to provide strengthening across cracked sections of structural members is to install new interior reinforcement. Reinforcing bars or dowels are simply installed in new holes drilled perpendicular to the crack surfaces. Epoxy injection is another successful method of internal strengthening. It is used on cracked walls, slabs, columns or beams which do not require reinforcement to restore. EXTERIOR REINFORCING Steel plates or channels are effective in stopping the spread of cracks. They can also provide exterior reinforcement for structural elements. EXTERNAL POST-TENSIONING Prestressing strands or tie rods with threaded ends may be used very effectively as external post-tensioning. JACKETS OR COLLARS Concrete members which are cracked or deteriorated throughout their entire cross section may be restored either by constructing a new reinforced concrete collar or by installing a series of tensioned steel straps around the existing members. SUPPLEMENTAL MEMBERS Supplemental members are simply new columns or beams installed to support damaged structural members or systems.