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4 Machine automation
The next step from having total stations is to examine machine automation. Often covered in these pages, so far it is only used by a few contractors in this region, though those that do can see a clear advantage in the amount of production.
Walid Daher from Bin Narwi, a contractor that has employed the methods said: “As many as seven bulldozers can follow the path graded by the first machine.”
He added that he was extremely greatful for the system, having used it in the past for other sites. “On this system, you just need to teach the operator how to use it, and he can do the job of both supervisor and foreman” he said.
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Mick Hales, from system manufacturer Topcon said: “Different people will tell you different, things, but I’m pretty sure [the Bin Narwi sites] will get triple the productivity from each ‘dozer.”
Add the cost and time savings up, and you will see they make sense for most larger roadbuilding projects.
Rollers
Having cut and filled the roadbed, the next step is to use a compaction roller. One of the best known developments in vibratory compactors is the oscillation
With dynamic compaction systems the compaction performance of a roller can be clearly improved.
These systems are based on the fact to stimulate the surface by vibrations in such a way that a grain relocation can take place into a closer position.
With the vibration compaction the material which has to be compacted is set in vibration by vertical forces. Oscillation rollers are particularly demanded for bridges. They allow high compaction performance and produce no damaging vibrations.
Just on such buildings the bitumen cools down faster by the sea breeze. That is no problem for the oscillation because with oscillation it is possible to work on even lower bitumen temperatures.
6 Asphalt plant
The smell of the hot tar mix might be an acquired taste, but the technology of the mixing drum has not changed that much in recent years, except the accuracy and the amount the drum can produce has increased significantly.
The main thing to know about asphalt plant is that two types exist, one with a batch heater which weighs the raw aggregates into a heater drum, where the batch is then heated up to temperature.
The hot aggregate is discharged into a mixing drum where filler and binder are added. The blend is mixed and discharged either directly into the delivery vehicles or into a small weighing and collecting hopper.
To increase throughput, the heater can be heating the next batch while the previous is being mixed. Batch heater plant is used where short production runs are common (a different recipe can be used on each mix) or where total volume is low.
Mobile batch heaters are available.The other type of asphalt plant is known as a continuous mixer. In the continuous plant, raw aggregate is brought up from ground hoppers at a precisely controlled rate and fed into a heater drum similar to that used in the asphalt plant.
Once heated it is immediately coated in the same drum (with the binder spraybars situated behind the burner) or in a smaller drum situated immediately behind it. Finished product is almost invariably discharged into a hot store rather than directly into delivery vehicles.
Changing mix is achieved by varying the feed rates of the aggregate, filler and binder feeders, with time delays so that the change of blend occurs at the same point in the coating drum.
7 Programmable logic controllers
Precise control of the mix is an absolute necessity, Modern plant will usually use a computer-based system known as programmable logic controllers.
Similar to the process control on a concrete batching plant, a series of gates can be set to open and close at precise intervals, thereby ensuring a perfect mix. This is all linked a computer, and very often to a computer network so that a plant manager can control the mix along a vast stretch of highway with a number of plant for example.
Traditionally, this industry has regarded the advancement of such computer control with some suspicion, but more and more plant managers are now seeing the financial advantages.
8 Grader
Graders are known as being the trickiest items on site to drive. The most common ‘old’ graders were the Caterpillar H or G series – which required the operator to be supremely well coordinated and probably with prehensile legs and feet.
Fortunately, the latest generation of graders have dealt with these problems. The M-series from Cat for example has dispensed with the multitude of levers, and even the steering wheel, in favour of two joysticks mounted on the end of the armrests.
These sticks, with a number of ‘fire’ buttons control pretty much all of the functions of the machine, with a readout making it as simple as anything else on site to drive.
Visibility is increased too, as the new machine has a six-sided cabin with a massive glass area, which enables the operator to see the circle of the moldboard. There are loads of other improvements as well, such as the compatibility with the company’s patented satalite guidance system – all of which make for a safer and much more productive piece of kit.
Those who think new technology means higher maintenance can think again. Shims and other wear parts have been designed to be accessible, as the old models had a reputation for being difficult to work on.
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