Long road

Dozers

 

Before a single groove can be cut into the ground, the surface must be cleared of shrubbery, tree stumps, lumps of building waste and any other awkward debris. For this the bulldozers come into action. Once on site, the first task of the ‘dozer is to beat a path so that less agile machines, such as the graders and scrapers can get in.

The front blade of the ‘dozer helps it power its way through the thick underbrush, while at the back, hydraulic ‘ripper’ teeth tear through the ground as they are pulled along. The rippers come very handy for breaking up ground that has been compacted over a period of time and won’t be easily stopped by roots or rocks in the ground.

By their very nature, bulldozers traditionally don’t offer their operators the most comfortable ride. In the past it was standard to have the operator exposed to the elements, while the tracked and un-sprung vehicle crashed over rough terrain. Modern ‘dozers are far more civilised. For example, the recently launched Caterpillar K-series bring in a full drive-by-wire experience, with no levers or hydraulic pipes coming into the cab. It also has a wiring harness with plugs to connect a laser or GPS-derived blade control system. This ensures level ploughing and makes sure the machine follows a constant course – all in the name of improving productivity.

Another advantage of having a bulldozer on site is that it doubles as a handy tow-truck. With wide tracks and gutsy motors, they can easily push wheeled equipment that may have become bogged-down, to safety. However for moving the big dirt you need a bigger scoop.

Diggers

Years ago, when diggers were known as steam shovels and operated from trucks shunted on impromptu tracks, large engineering projects needed very long schedules due to the tiny amount of earth the contraptions moved with each bite. Things improved with the arrival of diesel-fuelled hydraulic diggers with many times the amount of both reach and bucket capacity of their forebears.

However, until recently operating and maintaining such machines was a tough task as cramped cabins, poor cooling and literally hundreds of greasing points made them difficult to own. Today’s fully hydraulic, diesel-powered and computer controlled excavators are much better machines to work in or on. Although the number of ‘old’ brands has decreased sharply due to group mergers and a difficult market, several new makers from the Far East have brought in new products at competitive prices – forcing the old order to raise their game.
 

Nowhere is this more marked than the field of on-board electronics – or Telematics to give them their proper name. Modern machinery, such as new models in the line-up from US-based Terex boast considerable processing power, with a brand new control unit called e-EPOS that works with the piston pumps to ensure high efficiency and lower fuel consumption. Several other companies, such as Hitachi, now offer a sort of ‘black box’ recorder similar to those in aircraft, allowing the site manager to see how well the machine (and operator) have been working.

However, while the very big machines packed with technology make up one part of the highway construction industry, there is always a use for the smaller combined ‘backhoe loader’ type popularised by British-based JCB. Several Chinese firms such as Star and Wuhan now emulate this design, and as they use proven engines and hydraulics there is every reason to think that there will be more of them seen moving earth on site soon.

Scrapers

After digging and ‘dozing, the site might look something like a road, but it will be nowhere near flat enough to lay asphalt yet. The next step is to cut and fill with a scraper, removing earth from a high area and quickly moving it to fill a low area. Having evolved from crude trailers drawn by horses, the scrapers of today are now among the fastest and most energy-heavy pieces of equipment on site. There are several types, but most common on road building projects is the self-propelled type with a bowl, apron and ejector all capable of operating independently through a hydraulic system.

Generally there are two tractor units, one built-in for pushing and one separate unit pulling. It could be confusing and wasteful having two engines operating without synchronisation, but modern technology has the answers. Push-Pull scrapers such as the Dutch-built BOS TrackPower 155 have engine management systems that allow both engines to run in harmony. When the throttle is opened on the tractor, the control unit tells the rear engine to fuel up. In theory this should not only make the machine more efficient, but should allow the whole machine to be operated by one person.

However, scraper work tends to be done at full power as the machines need a relatively high speed to work properly and even with various electronic devices to save fuel, the consumption is still high. So that the machines don’t need filling up any more often than anything else on site, they are usually fitted with enormous tanks – sometimes as much as 1 400 litres.

Making the grade

The road is now smooth – but not smooth enough, so the grader is brought into action to perfect the surface, prior to paving. At its most simple a grader is a long wheeled tractor with a blade under the centre section and rear-mounted engine. The front wheels can lean up to 18 degrees to keep the grader balanced on a slope. In addition to the front wheels turning and leaning, a frame pivot just behind the cab can articulate the entire front assembly. This means that the chassis can be articulated and turned in one direction, with the wheels going the other way, to set up a sideways path where front and rear wheels are following a parallel track, allowing banks and slopes to be cut.

Driving a grader is about getting the infinitely adjustable blade just right, so that it shaves the precise amount from the topsoil, but in the past this was incredibly hard as the machines were entirely manual and the operator had to ‘feel’ what he was doing. The task was made even harder in view of the fact that very few machines even had seats. Today, the cabins are as modern as anything else on site. The new German-built Terex 23-tonne TG230 for example, boasts mirrors and lights all around, so that the driver can see forwards, backwards and sideways. On this model, blade adjustment is made easier with a GPS system, while front wheel drive is also an option.

At this stage, the road is nearly complete, a few passes with a wheeled compactor and the surface will be ready for asphalt. Not to be confused with the similar-looking road roller, a compactor usually has conventional pneumatic driven wheels at the rear and a large vibrating roller at the front.

After the soil has been watered down models such as the Ingersol-Rand 115 can use this vibratory function to exert more than double the machine’s kerb weight on to the road.
 

Two-lane blacktop

Road building has come a long way since the days of MacAdam. While he was happy leaving a road made from compacted dirt, today almost all highways are covered in asphalt blacktop. Asphalt is a mix of oil-based binders and aggregate and it provides a cost effective way of surfacing. The main problem is laying the sticky stuff evenly and at the right temperature for mile after mile.

For this a paver machine is brought on to site. Modern pavers are almost always self-propelled and they are rated by the width of road that they can apply, ranging from less than a metre, up to about 12 metres, and all designed to accommodate adjustable paving widths. The machine works by spreading the mix over a conveyer system and onto the road via a pair of auger screws.

From there, a team of workers measure the mix or ‘screed’ as it is laid down. It is hot and smelly work, but there are no shortcuts in getting a perfect surface. Unlike most other construction machines, pavers have remained essentially the same for many years, though some newer models like the SP-200 from US-based RoadTec can automatically spray an extra binder ahead of the screed, which can halve the amount of time the mix needs to set.

Rolling

Finally, following the paving crew is a fleet of steamrollers. Except of course, they are no longer powered by steam. Typically, three types of steamroller are used. The first, following the paver in its wake is the breakdown roller, so-called because it breaks down and compacts the asphalt.

It is usually a vibratory type and new technology, as used in the Bomag Intelligent Compaction System, allows digital measurement of the surface temperature, as well as a facility that automatically adjusts the vibrations according to how well the surface is binding. It is most important to get this stage right, as it is only too easy to destroy the hard work of the pavers . The next roller is a much more straightforward affair with nine rubber tires all inflated to exactly the same pressure.

The job of this machine is to further compact and to seal the asphalt. The tires are set in one row of four at the front and one row of five at the rear. They are staggered so there is no gap between them.

Once in motion it is very important that the roller stays going, or the tires will cool and the warm blacktop will stick to them. The final job before the line markers can move in, is the finish roller. This is just a simple, traditional steel roller. It runs from the centre of the road out to the edge, the way that rain will run off. With that the process is complete and the road just needs to be left to dry for a while. Properly constructed – and with a little maintenance – the new road should last a very long time.