Over a three-week period, Metrail removed and replaced over thirty individual joints on the J5–J7 section of the M621, a project that required over 80 tonnes of Permatrack mastic asphalt to be poured – and the work was carried out entirely at night.

  • Challenge
  • Solution approach
  • Technology

  • Execution

  • Result

The challenge

The J5–J7 section of the M621 has a number of underbridge sections that are subject to heavy traffic loading where the expansion joints had become irreversibly damaged. The Metrail scope required the removal and replacement of over thirty individual joints on the motorway totalling around 400 linear metres.
Planning for the project was originally based on full road closure. But when the local authority insisted on keeping some traffic moving, we were able to flex our programme to ensure the project was completed on time.

Facts & Figures

The work was carried out over
a three-week period between
February 22 and March 12,

The J5–J7 section of the M621

Removal and replacement of over thirty individual joints on the motorway totalling around 400 linear metres

Solution approach

The Metrail jointing wagon is a specialist vehicle developed by Metrail technicians to provide onsite support in all Metrail jointing operations. It was on-site throughout the contract programme and includes a cauldron for providing the molten PSB. The only additional plant required was a planer, which we used to cut out and prepare the old joints. When it comes to delivery, all jointing materials were delivered to the site in a mechanically agitated cauldron at a controlled temperature.


Joints: for this project we employed the IKO Permatrack H heavy duty joint.

Asphalt: the mastic asphalt used was a highmodulus material that uses a binder of SBS modified bitumen and Trinidad Lake Asphalt, which provides the low-temperature flexibility as well as the high-temperature stabilities required for heavily trafficked roads.


We began by marking out the new joint and planing the old joint out to a width of 500mm, with a 25mm rebate on the edge of the trench.
Old plates were then removed, and both the trench and the air gap were cleaned. Using the IKO PermaFLASH D300, we plugged the air gap and then applied a primer to all trench surfaces. After the primer came a first layer of molten PSB, which is a highly flexible material used for tanking the trench. It was applied to the base of the trench, and a galvanised steel plate was placed in the trench. The trench could then be fully tanked out and we installed a drainage channel and rodding box.

Next: installing the actual expansion material, known as PSB Strips. The strips were applied to the vertical faces of the trench, and then another coat of PSB was applied. We then placed a fibre glass sheet in the trench and filled the joint with Permatrack H.

We brought the trench up to the same level as the rebate so that steel side bars could be installed in the rebate. The joint could then be trowelled level and scattered stones were rolled into the surface until satisfactory embedment was achieved.

Last but not least: we removed the steel bars and filled the resulting grooves with PSB.


With Metrail’s aim to consistently deliver high-quality work safely and on time, we are pleased to report that this was achieved on the M621 joint replacement project, which was delivered to the full satisfaction of the main contractor as well as the client.

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