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Hand Laid Tarmacadam vs. Machine Laid Tarmacadam
Methods of laying tarmacadam – Hand Laid, Machine Rolled Bitmac
The vast majority of small and domestic tarmacadam or bitmac surfaces will be hand laid and machine rolled, with the bitmac brought to site in an insulated truck or hot-box to keep it workable. It is generally dropped onto the relevant area, raked level and rolled by a double drum Bomag™ type, ride-on roller / compactor.
In awkward and tight areas inaccessible to a ride-on roller / compactor it is acceptable to use a smaller vibrating plate compactor, though this should not be used for the full driveway as the finished surface may inevitably have unattractive lines in it. Neither will the surface have been compacted and compressed as well as it could have been with a heavy roller. A skilled operative working a ride-on roller / compactor will normally make five or six passes over the final surface or wearing layer to create a flat surface without any lines in the surface.
Methods of laying tarmacadam – Machine Laid Bitmac and Stone Mastic Asphalt
Larger areas and particularly commercial projects such as car parks, roads and sometimes very large domestic driveways should have the various layers of tarmacadam machine laid. Laying bitmac is a specialised job requiring a high level of skill but laying it with a tarmacadam laying machine takes this to another level. A tarmacadam paving machine will be used to lay both the base, or binder course and the surface course of bitmac. For areas of heavy use such as roads, stone mastic asphalt will be used as the final surface course, rather than bitmac.
Tarmacadam is delivered to site in an insulated truck to keep it hot and is emptied into the paving machine which then heats it up again, before spreading and screeding or levelling it. Once each course is laid and levelled, the surface is rolled and compressed by very heavy rollers. The rolling has to be carried out whilst the tarmacadam is still warm in order to compress it properly and quite a lot of water is applied to prevent it from sticking to the rollers – hence the steam which appears from the surface of the bitmac whilst it is being compacted and compressed.
Methods of laying tarmacadam – Specification to suit the job
For car parks and the like, laying and compacting the base course and the final course may be carried out over a period of days but for roads there could be an interval of up to a month between applying the two courses. Domestic driveways will normally have only two layers of bitmac (wearing course on a base course) whilst commercial areas and roads would have at least three (surface course, binder course and road base).
The traffic and intended use of the surface will determine the thicknesses of each layer and the size and type of aggregate contained within. And as with all tarmacadam, bitmac and stone mastic asphalt surfaces, greater care needs to be given to the final surface layer in order to ensure a smooth finish.
Only the very largest of tarmacadam contracting companies will have their own laying or paving machines and heavy rollers and it is quite normal and acceptable for the vast majority of capable contractors to hire a machine and driver / operator for the duration of the job – much as a farmer may hire a combine harvester for the few days or weeks of the year that it is required.