This technique is carried out for prestress concrete bridge. Endoscopy consist of insulting a rigid or flexible viewing tube into hole drill into concrete component or cable ducts and views them with light provided by optical glass fibre on external source.

This is most useful method for inspecting or detecting voids in the grout and corrosion in steel in the cube ducts.

It is also useful for detail examination of other part of the bridge structure which could not otherwise be assessed.

Endoscope are available as attachment for a camera or a TV monitor it however need experienced engineer to make assessment of most likely location of voids in the grout and probable point of entry of chloride into the ducts.