Fillmaster from Vencel Resil bridges the gap

Expanded polystyrene in the form of Fillmaster by Vencel Resil was chosen to upgrade the Hoole Road Bridge in Chester.

Originally built in the 1880s, the 15 brick pier road bridge was designed to take a maximum load of only 7.5 tonnes and was therefore unable to cope with modern traffic loading.

Cheshire City Council, the client on this project, faced several issues, the first of which was a weakness in the underlying soil on three of the pier sections.

This meant that a concrete block structure could only be used in two out of the five arches that needed strengthening.

Expanded polystyrene in the form of Fillmaster by Vencel Resil provided the perfect solution, being both lightweight and extremely strong.

Fillmaster has a track record in the UK of providing solutions for many different civil engineering applications where traditional fill materials are unable to meet specific site requirements.

It is particularly effective as a lightweight, cost-effective solution for bridge underfill applications where the structure requires greater support.

Patrick Savage, Engineering Manager from APB Group - the Civil Engineering Contractor carrying out the works - explains: "The weakness in the soil structure on these three pier sections meant that we needed a much lighter fill material than concrete to avoid overloading the underlying ground structure and Fillmaster provided the perfect solution".

The ground on the three sections of the bridge that used Fillmaster were capped off using a concrete base and the walls lined with a mortar based system, before the whole structure was waterproofed.

Fillmaster was then positioned on the concrete base and built up to the level of the horizontal sections that supported the road.

The load bearing properties of Fillmaster meant that the new structure provided the necessary support to the road.

The transfer of the load from the bridge was done using a special resin between the top of the Fillmaster and underside of the bridge structure.

Fillmaster is recognised for its loadbearing capabilities and the product is available in a range of sizes and strength grades - FM300 was used on this particular project.

It is the cellular structure of the Expanded Polystyrene (EPS) that gives Fillmaster its high strength-to-weight ratio, ensuring that the blocks are able to withstand the mechanical loads encountered on these types of projects.

Additional strength was provided on this bridge by replacing some of the existing iron sections with stronger bearing elements.

This central sections of the bridge, that crossed the railway, were of adequate strength as they were made from wrought iron.

The bridge extended over several hundred metres and the upgrading was required only on the outer sections, where iron was used, to a maximum load of 7.5 tonnes.

The unusual design of the bridge - being long and low - was originally intended to avoid the need for a hump back bridge over the railway.

Once the Fillmaster was in place, a block structure was used to create the end caps to each pier section, before finally finishing with a more decorative brick out wall.

Richard Nash, the Commercial Manager for APB Group , which carried out the upgrade, explains: "We used Fillmaster on the three pier sections that had the weak ground structure because it was both lightweight and strong".

"Fillmaster provided a lightweight solution that reduced strain on the ground, whilst supporting the bridge's structure." Fillmaster is available in a range of grades offering compressive strengths between 10kPa (FM50) and 190kPa (FM500) In addition to its physical properties, expanded polystyrene is easy to handle and compatible with rapid construction techniques, which is a major benefit for contractors.

As part of modern methods of construction, it can be transported to site in the minimum number of loads, producing less waste and with no negative environmental impact.

Expanded polystyrene has environmental benefits too as it is HCFC-free and non toxic.

The material is also extremely versatile as its closed-cell formation inhibits absorption of water and therefore avoids all of the problems of waterlogging and drainage that are associated with other fill materials.

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