Performance of recycled and secondary aggregates in the construction of the Newport Southern Distributor Road

Morgan Vinci Ltd were appointed by Newport City Council to design, build, finance and operate the Newport Southern Distributor Road (SDR). The SDR is the biggest local authority Private Finance Initiative (PFI) scheme in Wales. The new 9.5 km road will run from Duffryn on the west side of Newport to the Coldra roundabout (M4 Junction 24) in the east. It includes a new bridge to span the River Usk and the upgrading of existing roads to dual carriageway.

The SDR scheme is designed to improve the environment in the city centre, taking traffic away from residential areas, improving access to industrial areas in the east and south of the city and providing a new river crossing. Construction started during the summer of 2002 and it is anticipated that motorists will be using the road by the autumn of 2004.

During the pre-commencement phase, the construction, design, environmental and procurement teams combined to maximize the use of project derived excavated materials. Opportunities were also sought to utilize locally available secondary aggregates: by-products of the heavy industry historically located in the area. As well as complying with a high technical specification, the materials used had to meet strict environmental guidelines. The environmental considerations were imposed as conditions of the planning permission from the Local Planning Authority to protect the local environment, in particular the ecologically sensitive River Usk: a Site of Special Scientific Interest and Candidate Special Area of Conservation.

Overall, 95% of all aggregates used in the Newport SDR are recycled and secondary materials. This success can be attributed to the geographical location of the principal stockpiles of recycled and secondary aggregates, the ingenuity of the site team, together with a favourable specification. However, not surprisingly, the costs associated with transportation, particularly of the dense Steel slags, would probably make their use uneconomic other than within South Wales. It should be noted that primary aggregates have been used on the project. Natural stone was required for the Armourstone to meet Environment Agency requirements and specifications restricted the use of recycled and secondary aggregates for use as the pipe bedding material and the drainage blanket.

The project provides demonstrable proof that, through the use of risk assessments, recycled and secondary aggregates are environmentally acceptable and can be used in the vicinity of environmentally sensitive areas without adverse impacts;

The utilization of recycled and secondary aggregates on the project is shown in the table below.

The engineering fill material was tested against physical and environmental specifications to ensure suitability. Recycled asphalt was recycled on site for the capping layer. For the sub-base, Blastfurnace slag and Spent railway ballast were stabilized with cement to exceed the specification.

In addition to the normal engineering tests to ensure compliance with the specification, a number of chemical and leaching tests were carried out for environmental risk assessments. These included gas permeability tests for Pulverized-fuel ash (PFA), which was to be used as a mineral capping layer on a landfill site. The tests showed that the material was impermeable to gas and thus suitable for use.

The bulk of the earthworks is complete but some materials have still to be placed. This will be completed by February 2004.

The Blastfurnace slag and Steel slag were weathered prior to use. The only other processing required was crushing and screening. The sources of the materials were all effectively within the site.

The total direct cost saving of using recycled and secondary aggregates compared to the use of primary materials is approximately £1 million. In addition to the significant benefits for the construction project in using locally available recycled and secondary aggregates, a number of other benefits are also accrued:

• Reduced demand for conventional aggregates, reducing the environmental impact for the community;
• Fewer long distance haulage movements reducing the environmental impact in the local community;
• Encouraging innovation within Morgan Vinci;
• Promoting environmental beneficial practices, namely sustainable waste management, within the construction industry.

All materials were tested to ensure they complied with the Specification for Highways Work (May 2001) and chemical thresholds agreed with the Environment Agency. No departures from the Specification for Highway Works were required.