Video: GPR Scanning Precast T-Beams

Locating rebar and pre-stressed cables in precast T-beams with ground penetrating radar (GPR).

The bonded pre-stressed cables in the stem of the T-beam are marked with high-visibility orange. Overall, the four pre-stressed cables have a draped elevation and are closest to the bottom of the stem at the midpoint of the beam. There is some variance in the elevation profiles of the cables however. In the middle third of the beam, all four cables are aligned at the same elevation. In the outside third of the beam, the two outside cables rise to a higher elevation.

Structural reinforcing rebar in the tops and stems of the T-beams is marked in blue. A sample area 10′ long was marked up in two adjacent T-beam tops to facilitate demolition. Additional areas of the nearby cast-in-place concrete floor and wall were scanned as well.

Accurately mapping pre-stressed cables in these short stem T-beams is challenging due to the limited antenna travel area. There is very little room for the GPR antenna to access the surface, and larger units aren’t capable of providing enough data for accurate interpretation. Even with smaller high-end equipment, data samples are very short and require sufficient operator expertise. Concrete GPR LLC technicians are experienced with tall-stem and short-stem T-beams in a wide variety of environments.