All materials, of course, deteriorate in some measure from the ravages of time, exposure to the elements, and the effects of wear and tear. All factors considered, the performance of concrete compares favorably with other structural materials. The correct technique and material for a job depend on the extent of damage, the function of the structure, the availability of equipment and skilled manpower, the expected traffic or adverse environment, the time allotment, the importance of appearance and the available funds. The following information will help identify some of the more common types of concrete deterioration. Alkali-aggregate expansion is caused by a chemical reaction between certain constituents of some aggregates and the alkalies from portland cement. Cavitation is the erosion of concrete caused by rapid movement of a liquid such as water moving past or around a concrete mass. Efflorescence is the appearance of crystalline salts on a concrete surface. Fire damage is relatively easy to identify. The surface ordinarily is charred and spalled. Form scabbing occurs when form oil is improperly applied and fails to eliminate the bond between the form face and the concrete. Other problems are discussed in the article. Once the cause and type of deterioration have been established, the most effective and economical repair technique possible should be determined. Acid etching is sometimes sufficient in itself to repair the damage- for example, in a case of stains and uneven coloring. Dry-packing is the placement of a stiff mortar by ramming or tamping it. Grinding is a slow and expensive repair method, but often it is the most logical solution to certain problems with concrete- like leveling irregular slab surfaces. Jacking is the process of applying and fastening a material over concrete that provides needed performance characteristics. Mortar replacement is a repair technique usually confined to shallow holes. Other repair methods are discussed in the article. Selecting the best repair materials available is the final step in planning repair work. Bentonite is pulverized rock consisting of clay minerals that absorb 30 times their own weight in water. Linseed oil is usually used when scaling has occurred without severe enough distress to warrant the expense of an epoxy coating. Bituminous coatings are materials that can be processed from either asphalt or tar. Elastic sealants are used when cracks in concrete are expected to remain active for some time. Epoxy based compounds are important materials for many types of concrete repair like where adhesive is needed to bond plastic concrete to hardened concrete. Other materials are listed in the article.