Carlisle Southern Link Road
Project case study
Product: Cement Bound Granular Material (CBGM)
Volume: 11,800 tonnes
Main contractor: Galliford Try Construction Ltd
Client: Cumberland Council
Overview: Heidelberg Materials UK has supplied and laid 11,800 tonnes of Cement Bound Granular Material (CBGM) in two phases as part of the construction of Carlisle Southern Link Road in Cumbria. The material has been used to create the base layer of two sections of the new road in strict adherence to the Specification for Highways Works and relevant British Standards.
Project description: Heidelberg Materials UK was the surfacing contractor for the Carlisle Southern Link Road, a major infrastructure project in Cumbria designed to enhance connectivity and alleviate congestion in Carlisle.
The improved road infrastructure delivered through the £212 million project also enabled the development of additional housing in the area, highlighting the wider economic and social benefits of the scheme.
We supplied and laid 11,800 tonnes of Cement Bound Granular Material (CBGM), an hydraulically bound blend of aggregates, cement and water, which has been used to create a strong, durable base for two sections of the new road.
The constituent materials were sourced internally – the aggregate from Shap quarry and the cement from Ribblesdale – ensuring full control over quality and availability.
The CBGM was produced using our mobile Wirtgen KMA 240i plant, which was situated on site, and the material was laid in a single pass to a depth of 150mm and in accordance with all the relevant specifications, including those associated with health and safety, quality control and testing.
To ensure the highest quality, we invested in a high compaction paver and a custom-built roller. The paver had tracks instead of wheels, which provides improved stability and traction, particularly on softer or uneven bases. The tracks also help to reduce base damage by distributing the weight of the machine more evenly, helping to achieve consistent laying tolerances.
The roller was equipped with edge compactors to prevent any displacement at the open edge and ensure a clean vertical face for subsequent material placement. It also included an integrated joint cutter, which created transverse and longitudinal induced cracks immediately after initial compaction. These cracks were no more than 20mm wide and 75-100mm deep and span the full width of the road in accordance with specifications.
A bitumen emulsion was then poured into the cracks within the CBGM base layer to allow for flexibility under thermal movement. Filling the cracks with emulsion helps to accommodate expansion and contraction of the rigid structure of the road due to temperature changes. It also seals the cracks to prevent ingress of water and other contaminants, which could weaken the sub-layers or cause deterioration over time.
Compaction of the CBGM layer was completed using vibrating rollers and finalised with a pneumatic tyre roller (PTR). The purpose of compaction is to apply a controlled compactive force to the base layer, expel entrapped air, and produce a uniform, stable surface with good interlock and load-bearing capacity. The roller action ensures the surface is well consolidated and free from voids or weak zones.
The flexible rubber tyres of the PTR apply pressure unevenly across the contact area, producing a kneading effect. This helps to close surface voids, compress the top layer, and achieve a tighter, smoother finish on the CBGM.
Following compaction, a bitumen emulsion was sprayed onto the CBGM surface to act as a curing membrane. This helps seal the surface, reducing moisture loss, and supports the curing and strength gain of the CBGM. The sealed CBGM is then typically left for seven days before trafficking to allow the material to harden and reach sufficient strength.
Quality control during the CBGM production and laying was overseen internally with daily record sheets including:
- Moisture content testing of the CBGM to ensure it was produced and laid at the optimum moisture level
- Spread rate/batching record results
- Depth measurements
- Density test measurements
- Sample and test locations
- Construction period records showing the times of mixing, water addition, completion of compaction, and application of the curing membrane.
In addition, we used the UKAS-accredited testing facility, Construction Testing Solutions (CTS), which conducted rigorous on- and off-site testing to ensure the material and its laying conformed to all relevant Specification for Highways Works clauses (800, 811, 813.29, 817, 817.4, 818 and 820) and British Standards (BS EN 13242; BS EN 14227).
For example, during quality control, material samples were taken and compacted into cube moulds. They were allowed to cure for up to 28 days, and then crushed in compression tests to confirm that the CBGM material achieved the required strength.
The successful delivery of the project demonstrates our commitment to delivering high quality construction projects in strict adherence to specifications.
