Rawcliffe Bridge is a three span post tensioned bridge consisting of two balanced cantilever approach spans and a central suspended span, spanning over the Dutch River near Goole.
GENERAL OVERVIEW OF WORKS
The scheme included carrying out construction works to re-open Rawcliffe Bridge to vehicle loadings of 44 tonne and improve the current condition of the bridge structure. A new bridge deck and road construction were included with minor maintenance works. In summary the activities involved in the repair works included:
TENDON IMPREGNATION SCHEME
The council had performed inspections to the various bridge elements over the last 20 years and found the ground anchoring Macalloy bars to be in poor condition and the concrete encapsulated post-tensioned tendons to be suffering significant corrosion.
If these defects were not rectified it could have led to structural failure of the bridge. These defects, and the requirement to rectify without demolishing the bridge, raised some unique engineering problems. The replacement of the Macalloy bars is a complex but relatively well-known civil engineering process using tried and tested techniques. However, the corrosion protection of concrete encapsulated post-tensioned tendons within concrete bridges, without demolishing and re-building of a significant portion of the bridge, had not previously been completed in this country using our proposed techniques.
PBS procured a specialist sub-contractor with expertise in corrosion protection and worked in a collaborative fashion with the council to agree on an innovative method of corrosion protection that would achieve the required structural outcome but without the cost and time involved in reconstructing large sections of the bridge. The innovative technique we utilised was pumping under pressure a proprietary hydrocarbon and silicon-based material that has the ability to impregnate and saturate the full length of the tendons, with only small amounts of demolition being required to find the location of the tendons and for the pumping pits. This film pumped in under pressure formed a protective layer around the tendon. The film was able to travel the full length of each tendon using the voids within the existing grout and the interstitial spaces between the wires in the tendons. This film stops the existing corrosion process and provides improved resistance to future corrosion.
This was the first time this methodology and proprietary product had been used in the UK. The works were completed in two phases. Phase one was to demonstrate and evaluate the means and methods for the impregnation process on only one tendon. The information collected during the phase one works helped with the planning, methodology and budgeting for phase two. Phase two involved impregnating all forty tendons. Using the technique developed all tendons within the bridge decks were successfully protected from corrosion and the works were completed in a much faster and more economical manner that existing techniques would have allowed.