Effective repairs begin with a thorough inspection. With careful planning and preparation, surveys condition provide valuable information about the causes of deterioration and distress. The appropriate remedy can only be applied when the problem is identified.

In the context of serviceability and deterioration, insitu testing of concrete structure assist both diagnosis of causes of deterioration and assessment of the extent of hidden features which may lead to future problems. Both factors are of great importance where repairs are to be effective and long lasting. Nondestructive tests are generally defined as that which do not impair the intended performance of the element under investigation. This cannot be taken in its broadest sense when applied for testing concrete in structure. When damage is confined to near the surface and is of a small or negligible size, the insitu test is assumed as partially nondestructive. Indeed, they are nondestructive in relation to the main body of the structural concrete member.

The paper based on a survey conducted in Macabu dam briefly discusses the common defects noted in the overflow-drawoff tower. A simple systematic approach for examination and evaluation of the safety of such structure was than outlined. Overflow-drawoff tower is a structure used to control withdraw of water from the dam reservoir trough pipes.

Nondestructive tests for assessing the concrete deterioration of the overflow-drawoff tower were:

• rapid nondestructive methods, which are suitable for mapping large areas and recognizing areas of significance, i. e., ultrasonic pulse velocity, concrete cover by magnetic field test, half-cell potentials
• detailing small area by non-destructive and partial nondestructive tests. The used methods were rapid chloride test, depth of carbonation, pin penetration, permeability test, core extracted.

Keywords: Inspection; Overflow-drawoff tower; Carbonation; Nondestructive tests.