The path towards sustainability in road building. Steve Skinner reports.

Legislative and economic pressures are driving the road building sector towards more energy efficient and environmentally friendly machines and processes. Steve Skinner reports on the path towards sustainability.

When it comes into effect in 2011, Tier 4 Interim/Stage IIIB exhaust emissions legislation in the US and Europe respectively will lead to a new generation of road building equipment.

Ahead of the deadline, president of Bomag, Jörg Unger told iC, "There is no question that environmental issues must be addressed, but it does mean we've had to reduce our research and development budget for things beyond engines.

"The key to producing emission compliant equipment is managing the increased costs for our customers. We all expect a significant cost increase for compliant engines and over and above this we have to make fundamental changes to our equipment to fit the new engines, which again will have cost implications," he said.

Despite feeling that technology to make better equipment has been sidelined by the engine issue, Mr Unger told iC, "Bomag will show more at Bauma in 2010 than we did three years ago and I can confirm there will still be non-engine innovations on our equipment."

Ammann, like Bomag, believes that emissions compliance is an issue that is challenging every engineering department. "The new standards will call for more sophisticated powertrain components and additional functions to mitigate emissions," said Andreas Biedermann, head of corporate research and development.

"Stricter regulations are always a prompt for innovative solutions and we are taking this opportunity to have a serious look at new approaches for our compaction equipment. To this end, we believe we have found solutions that meet legislation yet don't impact on driver visibility or machine manoeuvrability," he told iC.

Asphalt

Mr Biedermann also believes that beyond engine emissions, environmental issues are a driving force in road construction generally.

"Today's challenge in the road construction sector is to build green roads with a minimum ecological footprint. Modern technologies to reduce CO₂ and lessen the demand for virgin resources must be applied to asphalt production and compaction to help create a sustainable environment," he said.

"We conceived the Ammann parallel drum for asphalt recycling some 20 years ago and we've continued developing in this direction to the extent that our newest parallel drums can use 100% reclaimed asphalt," he told iC.

Asphalt Drum Mixers (ADM) of Indiana, US, manufactures four models of stationary and portable recycling bins that allow the use of recycled asphalt for the production of hot mix asphalt (HMA). A spokesperson said, "Depending on conditions, up to 50% of the HMA can contain recycled material, which offers significant savings while maintaining asphalt quality."

As well as its recycling bins, ADM manufactures a four-strong Roadbuilder series of portable and stationary asphalt plants with production capacities of between 100 and 318 tonnes per hour.

Featuring a parallel flow system to maximise heat transfer through the mix, the Roadbuilder series adopts ADM's ‘flight' design to move damp aggregate in a rotating veiled pattern away from the burner, which the company says results in lower emissions than found with other parallel flow designs.

A significant development in reducing the environmental impact of asphalt production has been the emergence of warm mix asphalt (WMA). Astec Industries unveiled its second generation (G2) Double Barrel Green System for the production of the less energy dependent WMA.

The second generation unit offers simpler controls and a hot oil jacket that's -66% smaller than found on the G1. The G2 also eliminates the need to maintain the asphalt foaming valves, while the system no longer retains pressure once the foamed asphalt flow stops.

Other features include self-cleaning water injection valves that can be replaced without the need to remove the front cover, and visual flow indicators on the water injectors.

Terex Roadbuilding has introduced its latest foamed asphalt system for WMA based on an expansion chamber that means producers don't need any additives. The chamber mixes water and hot liquid asphalt and reduces mixing temperatures by up to -32⁰.

Product manager at Terex, Joseph Musil said, "This system is capable of producing up to 544 tonnes per hour of asphalt at a 4% water injection rate. Furthermore, through mixing at lower temperatures there's a reduction in odour, particulates, CO₂ and NOx emissions at the plant, while ‘blue smoke' is virtually eliminated at the truck and paver end of the operation."

Martin Diekmann of the construction materials and process engineering division at Wirtgen believes cold recycling will play a significant role in the future of road building. "Cold recycling offers a +30% saving in project costs over conventional road building methods, when you take into account machine costs and personnel. Depending on the project and its whereabouts, it also offers a reduction of between -20 and -50% in materials costs."

Wirtgen offers six cold recyclers from the WR 2000 with a working width of 2 m to the range topping WR4200 featuring two milling drums, a twin-shaft compulsory mixer, a spreading auger and a paving screed for recycling roads between 2.8 and 4.2 m wide.

"The environmental benefits gained from re-using 100% of the milled asphalt are massive," said Mr Diekmann. "You don't have to transport material, you don't have to buy ‘new' material, you don't need to use landfill for disposal and you only have to heat the bitumen to 175⁰ C, which requires a fraction of the energy that is required to heat aggregate for hot mix asphalt (HMA).

"Europe is just starting out on the road to cold recycling, but it's already very popular in Russia and we see this area developing substantially in the future," he said.

Next January Wirtgen celebrates the second year of a strategic cooperation that has seen it established as Bennighoven's official distributor throughout Russia, the CIS (Commonwealth of Independent States) and Serbia. "This partnership has worked well in offering customers overall quality across the complete road technology sector," said Benninghoven's Anne-Jan Klompstra.

Benninghoven manufactures around 100 asphalt plants each year, with its biggest units capable of producing 500 tonnes/hour.

"We can remotely access all of our customers' asphalt plants from the factory here in Mülheim to see what problems exist or determine when servicing is required," said Mr Klompstra. "This means we can stay very close to our customers, which we feel we need to do because it's our name written on the side of their asphalt plants."

In September, Benninghoven opened a new subsidiary office and spare parts centre in Graz, Austria. "The location is central to our Austrian customers as well as to neighbouring markets in Hungary, Slovenia, Croatia and Serbia," Mr Klompstra told iC. "This will enable us to offer improved spare parts availability in the region."

Paving

Across in the UAE, the new Yas Marina race circuit is about to host the season's final Formula One Grand Prix. While such a circuit might be considered the most unlikely venue for environmental advances, the precision demanded by Formula One means the track paving process has to be supremely accurate, which hones equipment and processes and results in minimal waste.

"The maximum tolerance allowed for track evenness is 2 mm measured over a longitudinal distance of 4 m," said Frank Dittrich, site manager for contractor Bickhardt-Bau at the Yas Marina circuit in Abu Dhabi.

"Through the use of Vögele's Super 1900-2 pavers fitted with AB 600-2 extending screeds we were able to make a significant contribution to the high degree of surface evenness with pre-compaction exceeding +92% before the Hamm tandem rollers even drove onto the circuit" he said.

The binder course for the 20 m wide circuit was paved in three strips using Vögele's Big MultiPlex Ski. "It's a fantastic solution," said Horst Henninghausen, foreman at Yas Marina. "The measuring concept enables the system to perfectly level out irregularities all on its own."

Control to increase smoothness is the hallmark of Roadtec's latest launch too, in the shape of its new Screed Boost. The system manages the settling of the screed when the paver is stopped and also compensates for the settling of rubber tyred pavers when halted, caused by the tyres compressing and allowing the screed to drop.

"Screed Boost pressurises the bottom of the screed lift cylinders while the paver's stationary and therefore prevents the screed from settling and causing a dent in the surface," said a Roadtec spokesperson. "The operator can adjust the pressure as needed and once the paver starts moving again Screed Boost simply shuts off and the screed returns to its free floating state."

The system features a delay switch that allows the boost to remain active for between zero and three seconds after the paver moves to help operators create a smooth transition in the surface.

Trimble launched its PCS900 paving control system last month, an automatic 3D screed control designed to improve productivity and surface smoothness by directly referencing the road design.

A Trimble spokesperson said, "The PCS900 will help contractors achieve excellent results, minimise asphalt usage and help keep projects on time and in budget."

The PCS900 is a 3D extension of the two dimensional PCS400 and contractors will be able to switch between the two. "The combination provides contractors with a choice of sonic sensors, slope sensors, a sonic averaging beam and 3D slope and 3D elevation control on each side of the screed, which will help in producing smoothed seams and fewer waves," said the spokesperson.

In China, Zoomlion asphalt mixing plants, pavers and compactors are being used on the 413 km long express Yuxiang highway linking Chongqing in the Sichuan province to Xiushan in the Hunan province.

Over 50% of the equipment on the project has either been bought or leased from Zoomlion and contractors attribute this to the reliability and above all energy efficiency of Zoomlion's road building offering.

Vice manager of the Yuxiang highway, Wang Yujie said, "Zoomlion's five asphalt mixing plants on the project have three distinct advantages. The burners are highly efficient and use less energy than comparable units in China, the electronics are stable and reliable and Zoomlion's service is beyond expectations."

Project manager with contractor, Chongquing Daotong Road and Bridge Engineering told iC that Zoomlion's quality was also a key factor in the use of 20 pavers and rollers on the project. "Product quality is absolutely the most important factor for this job in the Wuling Mountains, and we've kept on schedule because of the reliability of the equipment."

Greener future

While legislators force change, the road building industry is actively aiming to remain one step ahead in preserving the planet's resources. New processes and equipment have the potential to slash energy consumption and reduce the requirement for virgin materials. At the same time, improved accuracy is limiting waste and improving the smoothness of roads, which in turn will have direct environmental benefits for road users.