Eventually, spalling occurs, exposing the steel reinforcement. Rust 

 stains on the concrete surface are usually the first visual indication 

 of corrosion of the reinforcement. Once these visual signs are evident, 

 however, corrosion is well advanced, requiring costly repairs or replace- 

 ment of the structure. 



Damage from overloading may occur due to ship impact or may be gener- 

 ated by excessive pile driving forces during construction. The initial 

 damage may be only hairline cracks that go unnoticed. Subsequent inter- 

 mittent wetting may initiate corrosion of the reinforcement, causing the 

 cracks to increase in number and size, leading eventually to spalling. 

 Also, damage to concrete elements caused by freezing and thawing involves 

 penetration of the water into small cracks which are then expanded and 

 propagated by the forces generated when the water freezes. The common 

 causes of damage to concrete are summarized below: 



Chemical Mechanical 



Corrosion of Reinforcement Accidental Overload 

 Sulfate Attack Abrasion 



Chemical Reaction of Aggregates Freeze-Thaw 



Inspection data and accuracy requirements were established for the 

 underwater inspection of concrete structures (Ref 1). Equipment and 

 inspection techniques are required that can detect the presence and 

 location of cracks greater than 1/32-inch wide, diameter of rebar to 

 within 4% of the original diameter, concrete strength to within 12% of 

 the mean strength of the entire element, and location of rebar and depth 

 of concrete cover to within 1/4 inch. These data and accuracy require- 

 ments were derived from structural analysis criteria. 



Three types of inspection are distinguishable by the resources and 

 preparation needed to do the work and the type of damage or defect that 

 is detectable (Ref 1). Therefore, the type of damage detected depends 

 upon the level of inspection described below. 



• Level I - General Visual Inspection. This type of inspection does 

 not involve cleaning any structural elements and can be conducted 

 more rapidly than the other types of inspection. 



• Level II - Close-Up Visual Inspection. This type of inspection 

 generally involves cleaning of structural elements and normally is 

 restricted to the critical areas of the structural element. 



• Level III - Nondestructive Testing. This type of inspection is 

 conducted to detect hidden or incipient damage. Generally, the 

 equipment and test procedures will be more sophisticated than 

 either the Level I or Level II inspection. 



The evaluation test results presented in this report are for equip- 

 ment that would be used to perform a Level III inspection on underwater 

 concrete structures. Table 1 summarizes the purpose of each inspection 

 and the type of damage that each level of inspection will detect. 



