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Second Bank radar

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Working with the Columns
The fluted columns of the Second National Bank are among the most deteriorated elements on the building. SPR was tested to identify cracks and other discontinuities throughout the column drums. 
SPR testing equipment includes a transmitter and receiver that should be electromagnetically coupled to the stone columns. This required a molded medium with one side fluted to closely match the fluted configuration of the column and the other side providing a smooth outer surface for the equipment to be rolled over.

Surface Penetrating Radar (SPR) Explained

The primary technique employed during testing was surface penetrating radar (SPR). Using electromagnetic signals, radar was introduced in 1904. It was developed primarily for use in ground applications (ground penetrating radar or GPR). Since the 1970s, the use of GPR has grown, and the equipment is continually improving. Now, GPR has been extended for use with other materials and is commonly referred to as surface penetrating radar or SPR. SPR detects changes in the electromagnetic properties of materials such as dielectric permittivity, conductivity, and magnetic permeability, which in stone are a function of the stone material, water content, and bulk density. Our primary interest is the change in density that results from discontinuities: voids, cracks and the corresponding veining.

rader scanning
An early test of the system with a foam  contoured pad to created a flat surface for the radar receiver was not successful since the radar would not penetrate the foam.
The 3-D model of the column drum to the left combines the result of the radar scan with the surface conditions drawing. "

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