Post-Tensioned Special Investigation: M4 Wenallt Road Overbridge

Challenge

The M4 Wenallt Road Overbridge was highlighted as an asset that needed inspecting, based on either its condition or the date of its life cycle.

As a result, SOCOTEC UK and Ireland’s Structures and Pavements team was appointed by our client to work on the Wenallt Road Overbridge, one of a series of structures on the South Wales Trunk Road Agent (SWTRA) network.

Project Description and Client Background

The post-tensioned special investigation scope comprised of intrusive and non-intrusive techniques, with SOCOTEC accessing the underside of the structure using MEWPs and the top of the struture via trial pits, which were both excavated and reinstated by SOCOTEC.

Solution

SOCOTEC conducted investigations and testing in the area. This led to the excavation of trial pits, in order to expose concrete deck and behind abutment to access tendons. The team went on to test for corrosion, looking at the half-cell potential, depth of concrete cover, resistivity and depth of carbonation.

Duct tendons were subject to exposure, taking into account the duct location, tendon and strand exposure, as well as end anchor exposures, which looked at and considered the anchor location, anchor plate exposure, tendon and strand exposure.

Following the completion of site works, trial pits were reinstated, and concrete dust and grout sampling was sent for laboratory analysis. In addition to this, further laboratory testing was carried out for chloride ion, cement, sulphate, alkali.

SOCOTEC has a wealth of expertise and experience in carrying out post-tensioned special investigation projects throughout the UK. There’s a real multi-disciplinary approach in how SOCOTEC approach a multi-faceted project such as this one, combining site testing with in-house laboratory testing services. Our UKAS accreditation for many of the site tests carried out, as well as UKAS accredited laboratories also give us a healthy head start on the capability of our competitors.