Dan-Y-Graig Underbridge Refurbisments

Description

The work will involve replacing 2No asphaltic plug, bridge deck waterproofing, concrete repairs to end of the edge beams, jet washing and application of protective coating to the end face of beams above the piers including breakout of spalled and loose concrete from soffit of beam ends above abutments and piers and application of protective coating. Because of the process required to renew the asphaltic plug joints it is thought that the old sheet waterproofing system will be irreparably damaged during the works and so it is deemed necessary to replace the old waterproofing with an up to date polyurethane elastomer spray applied system which has a far longer life expectancy than the existing system. A red asphaltic sand carpet will be laid over the waterproofing to further protect it during any future maintenance at the bridge. In order to ensure continuity of the waterproofing, the polyurethane elastomer spray applied system and new bridge joints must be fitted from parapet to parapet. This will require that the existing asphaltic surfacing is removed and the concrete verges and central reservation on the bridge deck are excavated so that waterproofing can be applied directly to the bridge deck. The existing safety fence between carriageways will need to be taken down and set aside for re-use. The verges and central reserve will be reinstated with concrete and the safety fence re-fitted. The Western verge has 4 ducts set into the concrete that is being removed. They will be checked and if empty can be removed. They will not be replaced at this time. The East verge contains a drain fitted beneath it this will be removed during excavation and not replaced. Kerb drainage will be installed with rodding access points. As the joints and waterproofing are replaced each carriageway will be resurfaced with Hot rolled asphalt. Road markings and reflective studs shall be renewed. In order to carry out the work safely it is anticipated that it will be necessary to install a contraflow system so that an entire carriageway width of the bridge deck can be treated in one hit. The contraflow shall then be alternated so that the opposite carriageway can then be treated. The contraflow system will require enabling works to amend the existing crossover point adjacent to the roundabout with the B4591 and install a new crossover point approximately 50m to the north of the proposed works at Dan-Y-Graig Overbridge. Removal of approximately 100 metres of safety fence will be required at each crossover point, set aside then refitted once the bridge work is complete. Following a Principal Inspection and Special Inspection of the structure in May 2021 and March 2022 respectively, it was apparent that the ends of numerous deck beams below the expansion joints have suffered from concrete spalling with exposed corroded reinforcements and prestressing strands. However, the space between the soffit of the beams and top of the supports is limited to undertake any significant concrete repairs. Therefore, the proposed concrete repairs are limited to removal of the existing spalled and loose concrete from ends of all the deck beams followed by jet washing of the end faces of the beams above the piers to remove debris and apply cementitious protective coating to the ends of the deck beams with exposed reinforcements and prestressing strands including concrete repairs to bottom corners of the edge beams above piers. Concrete repairs also required to the west face of the northern pier. The contract is a NEC3 contract