Bid Bridge crosses the Bid Stream on the B2027 at Hildenborough and is the responsibility of Kent County Council. Built in 1876, it comprises of brick jack arches supported by cast iron beams, which were in need of strengthening in order to allow continuing use by all permitted traffic including the 40 tonne, 5 axle vehicles allowed on UK roads since January 1999.

The bridge had been temporarily propped, but the props needed removal before the onset of winter floods. The deployment of carbon fibre strengthening offered a quick and cost-effective alternative to overbridging pending reconstruction, albeit without some of the benefits of local widening which replacement would have provided.

Twelve six-metre long CFRP plates were glued to seven of the nine cast iron beams to provide the additional strength. Cast iron acts well under compression, but is brittle under tension. Carbon fibre plates, however, are very strong in tension and once bonded with epoxy resin, provide the necessary strength to maintain the structure's integrity.

The plates, developed by Devonport Management Ltd., are constructed from carbon fibre and epoxy resin. They are three times as stiff and fifteen times stronger than cast iron. The basic material, called a pre-preg, is one half millimetre in thickness and can be bonded together to form bespoke thicknesses demanded by each individual installation. The inclusion of tapers and localised reinforcement reduces stress concentrations in the adhesive and improves durability.

The installation is the first commercial project to adopt this non-prestressed method of strengthening cast iron beams on a highway bridge using tapered CFRP plates.