MUENOW & ASSOCIATES
Structural Engineers utilizing Non-Destructive Testing Techiniques

Test Techniques Utilized Continued

Resonant Frequency

Purpose:

Evaluates odd or regularly shaped members in mass numbers. Evaluates concrete composites, stone facades prior to and after installation for in-service safety, and is especially applicable to pre-cast pipes, boxes, and railroad ties.

Test Theory:

Objects vibrate at certain frequencies depending upon their size, shape, and weight. Every object typically has three resonant frequencies - longitudinal, flexural, and torsional. Test are conducted by two methods: self-resonance and forced-resonance. Self-rsonance allows for structural evaluation under actual service conditions, while forced-resonance allows for the evaluation of individual pieces or partial assemblies during fabrication or erection.

Typical Applications Include:

Magnetics

Purpose:

Detects and locates reinforcement steel in hardened concrete. This testing technique will also detect and locate most ferrous material embeddments, including anchors in granite and marble panels.

Test Theory:

Magnetic test equipment creates a known force field. This force field is disrupted by the presence of a ferrous embeddment. The amount of the disruption can be correlated to the presence, location, and depth of steel reinforcement. This test technique is especially applicable to columns, walls, beams, and slabs, where bar spacing exceeds concrete cover by a minimum of 50 percent.

Typical Applications Include:

Half Cell Potential

Purpose:

Evaluates and maps corrosion activity of embedded reinforcement steel.

Test Theory:

Research in corrosion has established upper and lower values of electrical potentials for reinforcement steel in concrete. Values below the lower limit indicate a high probability that no active corrosion is presently taking place. Values above the upper limit indicate a high probability that corrosion is active at the present. Values between the upper and lower limits indicate areas of prior or future corrosion activity and enables Isopotential Contour Maps to be generated.
Half cell potential measurements are made by traversing electrodes across a concrete surface. Test lines and grid patterns are normally established for recording data. This test technique only indicates corrosion activity.
There are virtually no size limitations nor shape restrictions to limit the usefulness of this test technique.

MAAI Background º Test Techniques I º Test Techniques II º Problem To Technique Guide º Job References

Muenow and Associates ° Charleston, SC, USA ° 1-843-768-2314
muenowr@bellsouth.net