When the M3 Hawley Lane Bridge started to show signs of excessive deflection under heavy traffic, engineers at Enterprise Mouchel devised a repair solution that included the installation of a new central bridge pier to support two existing outer piers.
To counteract changes to the deck’s dynamics and reinforce the bridge between the three structural piers, Sika CarboDur rods and Sika CarboDur plates were used – marking one of Europe’s largest applications of composite reinforcement systems.
Built in the 1960s, the concrete bridge had been under-designed to withstand the traffic volumes and live loads under which it is now subjected every day. With the span between two original outer structural piers proving insufficient to cope with the loading forces of constant and heavy traffic, a third pier proved the most suitable reinforcement solution to meet the increasing capacity demands.
However, as the initial bridge construction had not accounted for a third structural pier, further strengthening was required to accommodate changes in the structure. Approached early in the design process, Sika worked closely with the consulting engineers to advise material selection and properties required for a performance-based specification – in-line with Highways Agency best practice.
To achieve the required performance, carbon fibre plates and rods were specified as part of a complex repair and concrete protection solution. The use of carbon fibre offered an accelerated application process and enhanced performance properties when compared to traditional steel reinforcement. Set to be delivered by main contractor Birse Civils and specialist contractor Structural Systems UK Ltd, the £5 million project will see a total of 1,000mtr of Sika CarboDur Rods and 5,000mtr of Sika CarboDur Plates installed.
Sika CarboDur is a Carbon Fibre Reinforced Polymer (CFRP) system, designed to provide high performance structural stability in the most demanding reinforcement applications. Each plate, measuring 100mm wide and 1.4mm thick, was supplied by Sika in a variety of lengths of up to 13 metres to deliver exceptional reinforcing capability across the entire application area.
Utilising a team of skilled applicators, Structural Systems UK Ltd is completing the installation of the carbon reinforcement within a strict two month period. After grit blasting the underside of the bridge to improve adhesion, Sikadur 30 structural epoxy adhesive is applied to both the underside of the bridge and the carbon fibre plates. When placing the plates into position, full contact of the adhesive to the two surfaces guaranteed a long-term bond was achieved before a series of temporary supports were put in place whilst the adhesive cured.
The excellent performance of the adhesive ensured the application could be carried out throughout the night during the winter months, when low temperatures and condensation could cause problems for other adhesives. In situ, the Plates deliver exceptional durability and corrosion resistance – providing tensile strength of approximately 1,110 N/mm2.
Installed into the top concrete surface of the bridge, across two separate areas above the hard shoulder of the B3272/Hawley Lane, Sika CarboDur Rods have been specifically designed for the strengthening of concrete structures which have insufficient reinforcement or structural depth.
After cutting slots into the surface of the substrate to receive the Sika CarboDur Rods, SikaDur 30 structural epoxy adhesive was applied into the slots before the Rods were firmly pressed into place. A final layer of epoxy adhesive was applied to complete the application.
Non-corroding and very high strength, SikaDur Rods also ensure a simple application process for the contractor. Invisible once installed and with no leveling of uneven surfaces required – the Rods deliver mean tensile strength of 3,100 N/mm2 – vastly improving the bridge’s structural performance and resistance to loading.
Using the company’s extensive experience of structural strengthening – including in 2011 the UK’s largest application of ultra high modulus composite reinforcement at Embankment Tube Station – Sika will be closely involved at Hawley Bridge from initial specification to project completion. The company’s full range of structural strengthening systems are suitable for increased loading, change of use, column wrapping, as well as applications in the nuclear industry for protection against seismic activity.
On track to be delivered within a two month period, the project will be successfully finished to the highest standard thanks to a well-organised, detailed application process and with minimal effect on the road’s users – above and below the M3 Hawley Lane Bridge.