Approval for scheme to strengthen vital road bridge at risk from corroding concrete

Twm Owen, local democracy reporter

A £1 million project to strengthen a vital road bridge, over a canal, at risk from corroding concrete has been given the go-ahead.

The bridge carries the A472 dual carriageway across the Monmouthshire and Brecon Canal near Pontypool and it’s estimated an average of 35,000 vehicles drive over it every day.

Members of Torfaen Borough Council were told without the repairs, which could have been carried out for just under a quarter of a million pounds in 2019 the bridge, described as a “critical link in and out of Pontypool and a principal cross valley route”, would eventually have to close.

Highways chief Mark Thomas told councillors: “To maintain the main arterial route to Pontypool, from the south, we have to repair it or sooner than later we would have to at least lower the load limit and ultimately in time access.”

Monitoring

Testing and monitoring of the bridge has been ongoing since defects to the abutments were noted during a routine inspection in 2014.

A £240,000 repair scheme to prop up the bridge beams was prepared in 2019 but delayed due to works on the nearby A4042 and the Covid pandemic while the bridge was also extensively used as an overnight diversion route during the prolonged Gilwern to Brynmawr A465 improvements.

That meant work couldn’t be scheduled until late 2021 but was further delayed as the replacement of the central barrier on the A4042, between Pontypool and Cwmbran, was severely impacting traffic in and out of Pontypool.

A re-insepection in November 2022 found the condition of the abutments had “significantly worsened since 2019” and technical experts raised concerns the original repair strategy may no longer be suitable.

Mr Thomas said being mindful of costs officers had considered all options including “do nothing” but that was discounted as it is expected it would have led to the closure of the bridge within the next five years.

Of two further options considered Mr Thomas said the “slightly more expensive” plan to send a constant small electrical current, from a power supply, into the reinforced concrete to stop it from corroding was being recommended as it offered “better value for money.”

Electronic equipment

Installation of the electronic equipment will cost an estimated £777,281.00 but is expected to last 75 years with £5,000 required for annual monitoring while monitoring equipment will have to be replaced every 25 years at an estimated cost of £100,000.

The discounted option would have used zinc connected to the reinforcement to corrode “sacrificially” instead but would have cost £729,666.00 and the cost would have been incurred again every 15 to 20 years as the repair would need to be renewed.

Mr Thomas said the repairs are required as water enters the concreate and creates an acid that corrodes the steel reinforcements and that figure requested includes a 25 per contingency should costs increase.

The council was asked to approve additional capital funding of £407,000 towards the bridge repair with the £240,000 already available as well as a £127,115 underspend for a resurfacing project in the past financial year that came in an under budget to make up the total cost of just over £1m.

It is estimated the work will take up to 16 weeks, and could start in July, and will require roadworks to be installed on the bypass where it crosses the canal basin at Pontymoile.