19 June 2001
Give special attention to cracks found on the surface of a concrete
structure. Make sketches that show the length and direction of the cracks.
Overall cracking patterns and changes in crack length, width and direction with
time are meaningful data to a structural engineer. Photographs are helpful, but
only as a supplement to the sketches.
If there is evidence of significant deterioration, more detailed NDT
techniques may be used in a scheduled Level III inspection. Refer to the Level III
test procedures for concrete inspection for mechanical and electrical test
methods in Paragraph 5-5.4. The plan and sampling techniques shall be tailored
to the specific areas of concern.
Underwater Inspection. Use Figure 5-15 "Concrete Structures and
Attachments (Below Water) Checklist" to ensure that a thorough inspection of all
concrete structures and their attachments below water is done. An engineer
should explain to the diver exactly what should be looked for: number and size of
piles, type and depth of bulkheads. The engineer will evaluate the diver's
observations and determine the degree of corrosion.
Level III Test Procedures for Concrete Inspection. If signs of
deterioration or damage are found by Level I or II inspections then a Level III
inspection, involving either nondestructive or destructive tests, may be required.
Level III concrete inspections use mechanical and electrical test methods.
Mechanical and electrical test methods include:
The Schmidt test hammer may be used in order to compare the
relative surface quality of concrete at different locations on the
same structure. The instrument measures the hardness of concrete
surfaces by the extent of rebound of a spring-loaded steel plunger
in a tubular frame. The relative surface quality of the concrete,
which is also an indication of its compressive strength, can be
obtained. Surface texture may reduce values obtained.
Core samples are destructive in nature and should only be used if
other techniques cannot satisfactorily define the damage. Core
samples may be taken from selected areas in order to determine
petrographic analyses, and the actual compressive strength. Take
special care when setting up to drill a core, in order to avoid hitting
steel reinforcement, especially prestressed steel. Steel
reinforcement near the surface can be located by using a
pachometer (rebar locator). The length of the core sample should
be twice the diameter. After the core has been taken, patch the
hole with non-shrink cementitious mortar.