A46 Warwick Bypass Low Carbon Recycling Scheme

The Brief

The A46 Warwick Bypass was originally constructed in 1967. It is a two-lane dual carriageway all-purpose trunk road with grade separated junctions. The landscape is mainly rural and the road runs through a mixture of cuttings and embankments. Warwick Bypass has a history of numerous pavement failures. Surface deterioration ranged from fretting to potholing, open joints, wide, minor, and medium cracking plus water ingress. There have also been many temporary repairs each year (emergency interventions) to keep the carriageway safe; generally limited to shallow repairs.

Due to its importance to National Highway’s strategic network most repairs have been confined to the top two layers (Surface and Binder courses) which can generally be repaired overnight. Consequently, the deeper layer (Base Course) has rarely been removed. This deeper layer dated back to 1967 and contained Tar-Bound material. Tar was utilised in all pavement layers, including surface dressing, up until the mid-1980’s. Tar is a complex mixture of Hydrocarbons, some of which have been shown to be carcinogenic, while others are toxic to aquatic life and some are both.

A 3.5 mile stretch of the busy road had deteriorated to the point that, following a number of temporary repairs to ensure safety, a full depth reconstruction was needed, digging down 380mm to replace the lower layers of road surface. The usual approach to Tar-bound material is to remove it from site as it is classed as hazardous/special waste. This is an expensive operation involving transporting the material to a licensed tip and results in the material being added to landfill.

To minimise the impact on motorists the scheme was split into two phases; Phase 1 was to reconstruct the northbound carriageway and Phase 2 the southbound. This approach allowed the complete closure of either the north or southbound carriageway with contra-flow traffic on the other. Complete carriageway closure presented the opportunity for innovative solutions and the shortest construction programme.

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The Solution

Early contractor engagement and a strong commitment from National Highways to deliver a low-carbon scheme led to the development of a low-carbon pavement solution. Kier, Principal Contractor, and the pavement contractor, Aggregate Industries, agreed that full recycling of the existing carriageway would be the greenest and most cost-effective solution. All the existing Tar-bound material would be recycled back into the new carriageway using Aggregate Industries’ Ex-Situ Cold Recycled Foamix solution. Foamix effectively renders tar-bound material safe for reuse in the lower layers of pavement construction and in footpaths.

Foamix is a fully cold process and can be laid and compacted at a much safer ambient temperature which reduces the asphalt fumes on site that workers are exposed to. The Foamix was batched on site, next to the works, to minimise vehicle movements, increase daily volumes and reduce the schemes carbon footprint.

The pavement design followed industry standards and was agreed by National Highways through a departure process. The Foamix was overlaid with Aggregate Industries’ proprietary Warm Mix Asphalt (WMA), delivering further carbon savings and recycled content. For the surface course we used Aggregate Industries’ ProLay Silent asphalt. This is our Ultra low noise asphalt, -7.8dbA, which further enhanced the schemes environmental benefits.

Between both phases of construction approximately 42,997t of material was reused from the old existing pavement. Of this approximately 26,078t was hazardous tar bound material which would have been taken to landfill. Any remaining material not used was recycled back across the road network through other projects.

The use of WMA will also lead to a longer lasting pavement as the lower temperature preserves lighter fractions of bitumen for a less brittle material. Both Foamix and WMA deliver significant safety benefits during construction with reduced fumes and reduced risk from hot materials. Local recycling using one of our mobile batching plants delivered a significant cost savings to our customer.

National Highways Project Manager, Ryan Davies, said: “We have committed, through our net zero carbon plan, to rapidly cut carbon from road construction, maintenance and operations, and support the transition to zero emission vehicles.

“A vital part of meeting our ambitious objectives is having the support of our supply chain on schemes such as this. Through close collaboration with partners such as Kier and AI we are taking great strides on our journey to net zero carbon.”

Neil Leake, National Technical Manager at Aggregate Industries, adds: “Good collaboration and an innovative approach were at the heart of this scheme, with people working together to achieve the same low carbon scheme. We had some significant challenges to overcome to make sure this scheme could be delivered on time and still meet the low carbon goal we set ourselves.”

Kier Managing Director, Scott Cooper, said: "This is the first time that Foamix has been used on this type of road on the Area 9 Strategic Road Network and this work on the A46 scheme really demonstrates how innovation and excellent collaboration across the value chain is needed if Kier and our partners are to succeed with reaching our net-zero ambition and combatting climate change."