Barrett Byrd Associates

State of the art asphalt plants are no longer just about maximising production – they need to be energy efficient, quiet and environmentally friendly too. Claire Symes visited a new plant in Essex that meets all these criteria and a few more.

Getting the right quantity of high quality material to customers at the right time is the main philosophy behind design of most asphalt plants in the UK. But in recent years the focus of new facilities has shifted and now also encompasses a range of environmental issues as well as output performance.

Combination of production and environmental capabilities assembled in a strategic location are behind recent development of a new Bardon Aggregates asphalt and concrete facility in Harlow. The new asphalt plant was commissioned in October, while the concrete plant is due to open its doors in the next few weeks.

The new plant is well located for easy access to the motorway network and is also served by a new rail head that can deliver up to 1750t per hour of aggregates directly to the site’s aggregate terminal (see box). Harlow’s newest enterprise strengthens Bardon Aggregates’ presence in the south east and East Anglia through rationalisation of its operations at Hoddesdon and Bishops Stortford.

“Although our Bishops Stortford facility had a rail head, the short term lease did not lend itself to investment to upgrade the operations. The Hoddesdon site had limited storage space and no rail head,” says Bardon Aggregates project manager John Edgar. “The new plant at Harlow Mill has good access to the M11 and M25 making it ideal for customers who want to collect their materials.”

Harlow Mill’s new KVM plant is capable of producing around 240t of asphalt per hour and according to Edgar the plant has a number of innovative design features that maximise its efficiency. “Most Scandinavian production processes give greater consideration to energy consumption and environmental factors than their European counterparts. KVM is based in Denmark and is no exception to the rule,” explains Edgar. “Although KVM is essentially an overseas supplier, it has good service and long standing technical support facilities in the UK and gives added confidence.”

Bitumen delivery is one of the features on the KVM plant that both improves safety and boosts performance. The four 100t storage tanks are served by a stripping pump to offload the bitumen from delivery tankers. Stripping pumps more closely control the discharging process than the more conventional technique of blowing out.

Bitumen specialist Nynas Bitumen will be supplying Bardon Aggregates’ Harlow Mill plant with bitumen. “We supply the plant with three grades of conventional straight run bitumen and one polymer modified bitumen – Nypol TS – which is used to produce thin surfacing materials,” says Nynas Bitumen sales manager Miles Williamson.

The plant also has the capacity to blend bitumen on site but it is the Nypol TS that offers customers, and Bardon Aggregates, the greatest benefits. “Nypol TS has thixotropic properties which allows its viscosity to reduce as energy is added, for example during mixing,” says Williamson. “Once the mixing is complete, the viscosity increases and prevents binder drainage during storage and transportation.

“This not only improves end performance of the asphalt material but also removes the need to use costly release agents, that are not particularly environmentally friendly, to clean storage areas and trucks after use.”

Other performance enhancements at the Harlow Mill site include full enclosure of the aggregate terminal and concrete and asphalt plants. This not only reduces noise and dust pollution but also helps conserve energy through heat retention. “The plant features a number of power saving devices, including variable speed drives that mean the plant does not have to be on full power during lighter phases of production,” says Edgar. “There are also auto shutdown facilities to save energy if the plant is idle for a specific amount of time.

“Numerous testing points allow the site laboratory to create accurate quality control records and use of thermocouple and infrared temperature gauges in combination improves accuracy during production.”

Although the site is badged as a customer collection Express Asphalt site, the unit also operates a full delivery service under the Bardon Aggregates name. Customers can request material in quantities ranging from just 1t upwards enabling the facility to cater for almost every market. “The range of bitumen and aggregates stocked at the plant allows us to produce a wide variety of asphalt mixes, including recycled and coloured asphalts, SMAs and thin surfacings,” says Edgar.

Seven hot storage silos of varying sizes with a total capacity of 700t have been installed at Harlow Mill to add flexibility and rapid turnaround times. These storage facilities will also allow the plant to supply night resurfacing contracts, often without having to work outside normal operating hours.

Work on the 250m3 per hour concrete plant – one of the largest in the UK – is still under way but Bardon Aggregates is already looking to further improve share of the concrete and asphalt market from this facility.

BOX
Harlow’s rolling stones

All of the virgin aggregate used at Bardon Aggregates’ Harlow Mill site is delivered employing a specially designed rail head and dedicated rolling stock. The new rail facility was partly funded by a £2.1M Freight Facilities Grant from the Strategic Rail Authority.

“The grant has enabled us to develop the necessary sidings and buy our own train to deliver aggregate direct to site from quarries in Leicestershire and south Wales,” says Bardon Aggregates project supervisor Richard Oakley.

Edgar adds: “All 20 of the 100t (gross) wagons are bottom discharging to allow for a quick turnaround time on site and delivery of up to 1750t of aggregate per hour. The 21 bay stone terminal at Harlow can store up to 14,000t of material and is fully enclosed to help limit noise and dust pollution during delivery.

“From the terminal, aggregate is fed to the concrete and asphalt plant by a series of underground conveyor belts to further reduce the potential for noise and dust. Overall this plant is substantially quieter and more environmentally friendly than other plants.”

Secondary aggregates, such as asphalt planings, ash and crushed glass, along with bitumen from Nynas is delivered to the site by road.

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