Terahertz Source Inspects Bridge Components

Terahertz waves could be especially useful in the safety inspection of bridges that use prestressed concrete (PC) steel wires hidden inside external cables covered by resin jackets.

That's the conclusion of researchers at Tohoku University who developed an optical measurement system able to penetrate polyethylene resin and similar resins. This allows nondestructive imaging of the inside of PC steel wire without removing the resin cover, as the terahertz waves efficiently reflect off metal surfaces within the resin.

Comparison of a photograph and a terahertz image of a prestressed concrete steel cable. The polyethylene outer mold was partially removed. Courtesy of Yutaka Oyama.

External cables are important structural elements for dispersing loads in extradosed bridges, which are cable-stayed structures usually featuring a box girder deck. Resin coatings also make external cables resistant to corrosion.

Destructive inspections of the cables, in which the outer coating is removed from the cable, run the risk of allowing moisture to penetrate the wires and corrode them after the inspection has been completed.

Results of this research were presented at the CLEO Pacific Rim conference held in earlier this year Busan, South Korea.