Voids were found in the vertical post tensioning duct contained in the V shaped piers at the ends of the footbridge. The ducts contained macalloy ties that provided vertical restrain to the ends of the deck. The footbridge was located adjacent to a busy road and the client was concerned that repeated wetting of the piers could lead to chloride induced corrosion of the post tensioning.
Whilst the post tensioned ducts had been grouted an investigation found voids were present, although the extent was not known. The macalloy bars occupied most of the duct interior leaving a small partially voided anulus around the bars. The remedial injection would need to seal the voids.
Injection ports were drilled at regular centres to determine the extent of the voids and packers were installed to allow injection of the cementitious grout. Topbond worked closely with the grout manufacturer, who provided on-site technical support during the works. The grout was stored in a heated room and sieved before use to ensure consistency of flow. A small pressurised system was used to inject the grout. Post injection inspections proved the success of the technique.