Case study

Southampton Road Subways (Portsmouth)

The project

The two Southampton Road subways, located in Portsmouth, were constructed circa 1956 for the purpose of providing pedestrian access under the A3 Southampton Road dual carriageway, comprising a reinforced concrete box structure with a clear square span between the subway walls. A principle inspection of the structures had identified significant cracking, low concrete cover in certain areas and inadequate sealants of joints, amongst other associated defects, as well as extensive fire damage to one of the subways. APA Concrete Repairs Ltd were therefore appointed to undertake an extensive refurbishment programme, in order to restore and improve the structures for modern day use.

The solution

Varying works were carried out to the two subways, with both requiring extensive concrete repairs and the replacement of expansion joints, prior to the application of various protective coatings. To establish a dry, leak free subway, polyurethane was injected into the walls and soffits. The walls of the first subway were completely re-rendered before anti-carbonation and subsequent anti-graffiti coatings were applied to the walls and soffits of both subways. Concrete repairs were also undertaken to all stair treads, risers and landings, and all handrails were either replaced or repaired and re painted, in order to match the newly coated underpass.

The outcome

The refurbishment of the two subway structures was completed by August 2018, ensuring these essential pedestrian access routes could be promptly re-opened to the public. The provision and application of the various protective coatings and polyurethane resin injection will provide a protective barrier against potential future water ingress and resultant corrosion. The application of a masonry paint and replacement of surrounding handrails provided the largely improved aesthetic appearance that these structures required.

Materials Utilised

  • Sika MonoTop 620
  • SikaGard 552W Aquaprimer
  • SikaGard 550W Elastic White
  • SikaGard 850 AG

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