Concrete has excellent durability, and normally requires little or no maintenance, but good performance depends on good designs, details, materials and workmanship.
Why then should repair be necessary? The answer lies in a subjective consideration of the facts concerning any particular concrete unit that has been deemed unsatisfactory in its present condition. The deficiency may be structural, cosmetic or some combination of both.
Unsatisfactory performance in service could arise as a consequence faulty design, the use of unsuitable materials, improper workmanship, undue exposure to abnormally aggressive environments, excessive structural loadings or any combination of such factors.
If or when repair and restoration of concrete becomes necessary, the objective of any remedial work should be to return the concrete to a satisfactory condition of structural adequacy, durability, and/or appearance at a reasonable cost (commensurate with the benefit to be derived).
A rational repair programme should start with a diagnosis, or evaluation of the damage, and then progress through selection of materials and method to preparation of the deficient area and, finally, to application of the repair. If each of these steps is undertaken correctly, and at the proper time, then a satisfactory repair will be obtained.