First publishedin World Highways
Work in full swing on the Acton Swing Bridge
Aggregates Industries recently lightened the load for the 73m-long bow string truss Acton Swing Bridge in England. When opened in 1933, it was the first floating swing bridge in the UK – floating on a pontoon.
The 84-year-old bridge, which is cared for by the Canal & River Trust charity, carries the busy A49 road over the River Weaver Navigation, in the county of Cheshire. A recent €1.7 million complete refurbishment included strengthening works to the underside of the bridge as well as improvements to its appearance.
Core to the project’s success was the ability to enhance the bridge’s structural integrity to allow for heavier traffic. The challenge was to do this without an increase of mass – given the required 2.5m allowance for boats passing underneath.
As such, Aggregate Industries’ Lytag secondary aggregate - up to 50% lighter than normal weight aggregate - was chosen by lead contractor Kier Construction. By using Lytag to replace the infill with the framework, the weight was effectively reduced from 2,400kg/m³ to 1,650kg/m³. This gave increased flexibility and durability for Kier, while ensuring an increased overall strength. The approach also negated the need for quarried aggregate, helping to reduce material requirements and ensure efficiencies.
With works now complete, the contract saw Aggregate Industries supply 100tonnes of 0/14mm Lytag - a tailored blend of aggregates specifically designed to offer a greater reduction in concrete density.
Lytag replaced the infill with the framework, effectively reducing the weight from 2,400kg/m³ to 1,650kg/m³
The design freedom afforded by Lytag offers the same level of structural performance as normal weight concrete, explained Steve Curley, general manager for Lytag at Aggregate Industries.
“However, it is significantly lighter, thus reducing the dead load of a construction. In projects such as Acton Swing Bridge, where strengthening works need to be achieved without resulting in an increase to size or mass, this product can really make the otherwise infeasible achievable.”
The lightweight concrete has a density of 1,850kg/m³ using natural fines (normal weight concrete of 2,400 kg/m³). If fines are used in conjunction with the 4/14mm aggregate, the density can be as low as 1,650kg/m³.
Using Lytag within the design can not only reduce the thickness of the slab, columns and foundations but reduce the amount of rebar required, resulting in a quicker more cost-effective greener structure.
Aggregate Industries is a member of the Swiss global building materials provider LafargeHolcim Group.