Paving the way

08 May 2008

Main contractor Coco Paving has just completed reconstruction of a 10.4 km section of Highway 401 in

Main contractor Coco Paving has just completed reconstruction of a 10.4 km section of Highway 401 in Ontario, Canada using a Gomaco PS-2699 placer/spreader and a GHP-2800 four-track paver (pictured).

Claire Symes reports on the latest developments in the industry.

Rising traffic volumes and the need for cost-effective maintenance is placing higher demands than ever before on both road surfacing materials and the equipment used to lay them. These demands are driving research and development of new materials, techniques and equipment which can complete the work quickly to minimise disruption to traffic.

Investment in the strategic road network of developing countries through loans from development banks is also helping to ensure continued growth in the road building market. According to the World Bank, supporting infrastructure upgrades in less developed countries plays an important role in promoting economic prosperity and reducing poverty.

But no matter where the road is or how it is funded, the construction basically falls into one of two categories - asphalt or concrete. Some regions prefer the hardwearing, lower lifespan costs of concrete, but the higher traffic noise and costly and disruptive reconstruction is considered less desirable by others. The flexibility offered by asphalt surfacings in terms of both laying and maintenance, in addition to its smoother, quieter ride and potential for recycling mean that it is more popular than concrete in some parts of the world.

Going green

Environmental concerns mean that many countries are increasingly turning to recycling methods to prolong the life of asphalt roads. Technological advances are also enabling the technique to be used on higher grade roads.

“The (asphalt) recycling market is really growing - we have recently sold machines to Iran and China,”said Jacques Bonvallet marketing manager for the Fayat Group which owns both Bomag and Marini. “It's not just the environmental benefits of recycling that are driving the growth, the rise in crude oil prices means that recycling has become more financially attractive.”

The approach to recycling and specifications vary from country to country - some prefer in-situ techniques while other favour ex-situ methods. “Disposing of planed-out material is a problem so the trend to recycle will grow, but there are a number of different techniques and none have emerged as the definite solution as yet,”said Dynapac Spa president Augusto Chiellini.

The type of bitumen binder used also varies but, according to Mr Bonvallet, bitumen emulsions give better results than foamed bitumen. “Use of polymer modified emulsions helps to boost durability and performance of recycled pavement, opening up the benefits of recycling to a wider audience,”he said. “Foamed bitumen is better suited to stabilisation techniques than recycling.”

Wirtgen is also seeing an increase in demand for recycling equipment and one of its WR 2500 S machines has just completed work on China's first large scale cold recycling project. The Liaoning Transportation Department (LTD) used the Wirtgen machine to reconstruct the top 150 mm of a 19 km length of the Yingda Road which links Yingkou with Dashiqiao.

More than 15000 vehicles - 50% of which are heavy trucks - traffic the road each day. LTD used bitumen emulsion in the recycled mix to ensure the road could stand up to this heavy loading, as well as cope with the region's harsh winters, without cracking.

Caterpillar has recently added to its recycling capabilities through launch of the RM 300 Rotary Mixer and another new recycling machine, the RM 500, which will be released later this year. “Field testing of the RM 300 is going well,”said Cat road construction division manager Hamid Lavassani. “The machine is an upgrade of the RM 250. Improvements include easier maintenance and comfort for the operator, as well as a new transmission which delivers 98% efficiency.

“Recycling makes sense and should continue to grow,”he added.

“We are working with our customers to ensure they are getting the optimum performance.”

Added performance

Fixed curb levels and existing street furniture means that engineers cannot just increase the thickness of a pavement to meet demands for more durable road surfacings. But getting higher performance from thinner layers of asphalt takes more than just improving the mix. Improving the bond between the layers - in the form of a bond or tack coat - is also essential.

Mr Bonvallet said, “Use of tack coats is becoming more important. Recent calculations using software which analyses durability showed that using a tack coat can multiply the lifespan of a pavement by up to 2.8 times. Use of bitumen emulsion tack coats instead of conventional cut back based ones will also become more common in the future because the break can be accurately managed, giving a more consistent result.”

Geotextile manufacturer Huesker agrees that a good bond between asphalt layers is essential for sustaining high traffic loading. The company claims that use of polyester reinforced grids in combination with tack coats can help to further boost pavement strength.

Milling machines

Accurate planning or milling out of old surfacing materials is essential to achieving a good finish on the new surface and is also important for ex-situ asphalt recycling schemes. Many contractors now prefer to use cold planing techniques because of the environmental and health and safety advantages over hot planing methods.

All of the recent milling machine launches from Marini, Cat and Wirtgen are in the compact size range and the designs focus on manoeuvrability.

Wirtgen's new W 35 and W 35 DC are designed for milling out small areas in roads or pavements and have a maximum planning width of 350 mm. The three-wheeled W35 can mill to a maximum depth of 60mm, has an operating weight of 2.4 tonnes and is powered by a 31.5 kW engine.

The ‘DC’of the W 35 DC denotes ‘deep cutting’and it can mill to depths of up to 110 mm. The 42.5 kW powered machine's standard milling width is 350 mm but an optional milling drum assembly allows the width to be expanded to 500 mm.

Marini has also added three new cold milling machines to its line up. The MP 600 was unveiled by Marini America at ConExpo in Las Vegas, US in March while the MP 2000 E debuted at Samoter in Verona, Italy last month. Both machines have been designed for use in restricted spaces.

The wheeled MP 600 is the smaller of the two new Marini machines and has a standard cutting width of 24 in (610 mm). The machine is powered by a 175 hp (130 kW) Deutz four cylinder engine and features four hydraulically adjusted strut towers with a swing-out capability on the right rear tower to allow for curb flush cutting.

The MP 2000 E can be fitted with different milling drums to allow it to cut widths between 1.3 and 2 m. The tracked machine comes fitted with grade and slope levelling systems which are controlled by an on-board computer. According to Mr Bonvallet the machine has a number of advantages over previous models, “The MP 2000 E is shorter and 2 tonnes lighter than the older version which makes it easier for transportation and better suited to urban sites.”

Marini America's new MP 2100 cold planer has a cutting width of 83 in (2100 mm) and is designed to remove a half lane of road surface in one pass, and has a maximum working speed of 98 ft/min (30 m/min). The machine features quick change cutting teeth and holder and simplifies maintenance through its onboard computer system which monitors and controls the machine's functions.

Cat has upgraded two of its cold planers - a move which is partly down to the rebranding of machines formerly marketed under the Bitelli name following Cat's buyout of the company in May 2000. “The Bitelli name is gradually being phased out - some of the paving equipment still carries the Bitelli branding but that will also change over to Cat next year,”said Mr Lavassani.

Both the machines are larger than the other ‘compact’planers but Cat classes them as compact because they mill a narrower width than its other machines. The 30 tonne Cat PM-200 cold planer replaces the Bitelli SF 200RS while the 39 tonne Cat PM-201 replaces the PM-565B. Both machines are described as half lane milling machines and are designed to carry out full depth removal of asphalt or concrete pavements in a single pass.

The PM-200 and PM-201 are powered by Tier 3/Stage IIIA compliant six cylinder 429 kW Cat C18 ACERT diesel engines which have been specifically optimised for milling. The polyurethane tracked machines are hydrostatically driven. The PM-200 is fitted with a 2 m wide rotor and has a maximum cutting depth of 320 mm. The PM-201's cutting depth is lower at 300 mm but the machine can be fitted with three different rotors to suit different materials.

Terex's new milling machine, the PR 950, is definitely not a compact mode l- the company claims that it is the largest milling machine currently on the market. The PR950 is powered by a 950 hp (708 kW) engine and can mill widths of between 7 and 12 ft (2.1 and 3.6 m). The tracked machine can either be mounted on three or four tracks and can plunge cut to 15 in (380 mm).

Paving equipment

Paving operations usually directly follow the planning process in order to minimise the length time that a road or lane is closed. And there have been plenty of new machine launches for both the concrete and asphalt market so far this year.

Vögele's newest paving machines include two compact units. The Super 600 is designed for use on footpaths, cycle lanes and small sections of road, while the Super 800 features the same compact design but has a higher performance, larger pave width and a greater compacting intensity.

The Super 600 is powered by a 40 kW Deutz engine which allows pave speeds of 60 m/minand a laydown rate of up to 200 tonnes per hour. The paving width of the machine can bevaried from 0.5 to 2.7 m with use of cut-off shoes or bolt-on extensions. The Super 800 has a slightly larger 42 kW engine which allows the machine to lay material at a rate of up to 250 tonnes per hour over widths of up to 3.2 m.

Vögele America has upgraded its range of lane-width pavers. The wheeled paver range has been updated with the 8 ft (2.4 m) 2111W and 2116W and the 10 ft (3 m) 2219W. Vögele's tracked pavers have now been upgraded with the 2116T and 2219T, which fall into the 8 ft (2.4 m) and 10 ft (3 m) size range, respectively.

Ingersoll-Rand has added four new pavers to its range - the Titan 8820 and the 5110, 5160 and 5170 highway class pavers.

The 17.5 tonne Titan 8820 can be used to install roller compacted concrete, cement treated base, non-treated base, stone, soil cement and asphalt and is equipped with an electronic paver management control unit. The paver can be fitted with a variety of screeds which allow it place concrete and asphalt up 13 m wide and 0.3 m thick.

The track mounted 5110 and wheel mounted 5160 and 5170 pavers have a maximum paving width of 8.5 m and a hopper capacity of 12.3 tonnes, which gives the paver a practical production rate of 730 tonnes per hour. The 5110 has a maximum paving speed of 73.2 m/min while the 5160 and 5170 can achieve 64.9 m/min.

Cat launched two new asphalt pavers at ConExpo in March. The AP-800D is a medium sized wheeled paver designed for new construction, overlay and maintenance work. The larger AP-1055D features dual operator stations and is available with either a steel track undercarriage or the Mobil-trac undercarriage which gives the paver the manoeuvrability of a wheeled machine.

According to Terex, one of its latest machines - CR662RM RoadMix - can help boost both on site productivity and the final finish of the asphalt surface. The Road Mix is a material transfer vehicle which enables contractors to keep the paver continuously supplied with asphalt. The machine has two sets of two counter rotating augers which ensure the material reaches the paver in the optimum condition.

“The CR662RM can also be fitted with a screed to allow it to be used as a paver on smaller contracts,”said Terex Roadbuilding vice president Tony Araman. “The machine is undergoing final testing at the moment and should be commercially available later this year or in early 2006.”

Terex, Guntert &Zimmerman and Gomaco all introduced new paving machines for the concrete market at ConExpo.

According to Terex, the new Series B SF2204B HVW concrete slipform paver is the only paver that can hydraulically adjust the paving width from 2.4 up to 6.1 m in minutes, rather than the hours taken by conventional mechanical machines.

Terex's other new machine is the Bid-Well BCG3303 curb and gutter paver which features a three track low profile design which can also be used as a small utility slipform paver. The machine features Terex's modular curb forming system which enables profile moulds to be changed in minutes and lift the mould without dismantling.

G&Z's new PS1200 Placer/Spreader features a roll-in, roll-out conveyor and can pave widths of up to 12 m. The machine is also is self loading and can be transported in a single load under 3.66 m wide.

The V2 mould is the latest machine to be added to Gomaco's line up and features a dual mould system that is hydraulically adjustable for paving at different widths. The company claims that this system makes width changes “fast and simple and [it] will even make on-the-go changes for tapered slabs”. The machine features separate mould controls on each side and is available with a curb profile on one or both side for municipal paving.

Final finish

No matter how good the quality of the surfacing material or equipment that lays it, if it is not properly compacted then the material will not achieve the desired strength and durability. Compacting equipment is also used in the preparation of road base layers and is also critical to the final finish but calls for slightly different equipment.

The critical nature of compaction is highlighted by the number of new product launches into this field over the last few months. Bomag has launched eight new pieces of compacting equipment.

While Hamm, Ingersoll Rand, Dynapac, Multiquip and Ammann have also all added to their compaction ranges.

Most of the recent product launches focus on improving operator comfort and visibility and integration of computer technology to improve the final finish. Ingersoll-Rand's DD-158HFA now features a rotating and sliding cab to give full visibility which means that operators will no longer have to lean over the side of the machine to view the drum edge.

Bomag's latest offering includes eight new rollers and three reversible plate compactors. The 32849 lb (15 tonne) BW213DH-4 BVC single drum vibratory roller features Bomag's Variocontrol Intelligent Compaction system which automatically adjusts the output energy of the drum to optimise compaction. The system also alerts the operator when the maximum density has been achieved, avoiding unnecessary passes and over compaction.

Improved visibility is also a feature of Bomag's new BW141AD-4 and BW151AD-4 tandem vibratory rollers. The machines both have slanted drum support legs that give operators a clearer view and can handle a variety of lift thicknesses and applications.

Hamm has extended its range with three new machines - the HD O70V, the HD O120V and the 3412 VIO - which are all oscillating rollers. According to Hamm, the oscillating movement is more efficient than conventional vibration through higher travel speeds and more effective compaction.

Dynapac launched several new pieces of compaction equipment at ConExpo, including the CC800, CC900 and CC100 small tandem asphalt rollers. The new machines feature a spacious operator's platform, which is isolated from the vibration of the rollers, and has been designed to minimise maintenance.

Ammann's new AP 240 H pneumatic tyred roller has been designed for mid to large scale compaction of asphalt and loose or semi-cohesive materials. The weight of the machine can be varied to suit the job site need. Ammann's other new roller is a 10 tonne articulated machine - the AV 100 X - which features a double joint that allows crabbing of 150 mm to both sides.

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