We drive on roads and highways and park in asphalt paved parking lots every day, but have we ever taken a moment to think about what manpower and equipment is necessary to construct these large areas of pavement?
Here is a list of equipment used to construct these surfaces and what they are used for:
Milling Machines: A top layer is milled off the existing pavement to provide a relatively smooth surface on which to pave. Milling is also commonly used to remove a distressed surface layer from an existing pavement. Milling also produces a rough, grooved surface, which will increase the existing pavement’s surface area when compared to a smooth surface. Milling is advantageous for several reasons: the most important being efficiently removing deteriorated pavement that is unsuitable for retention in the overlaid pavement. Other advantages to milling are: providing a highly skid resistant surface suitable for temporary use by traffic until the final surface can be placed; allows curbs and gutter lines to be maintained or reestablished before Hot Mix Asphalt (HMA) overlays.
Sweepers: A sweeper cleans the surface of the road after it has been milled. This is necessary because excessive dust and debris on the ground can prevent proper bonding between the asphalt and base course. Large pieces of debris can also cause non-uniform compaction of the asphalt. It is especially important to clean the road after milling, as small rocks and pebbles can fly up and hit windshields of oncoming traffic causing damage to vehicles.
Dump Trucks: Dump trucks move the hot asphalt from the plant to the jobsite. There are many kinds of dump trucks:
- Bottom or Belly Dump: Bottom dump trucks unload their payload by opening gates on the bottom of the bed. Internal walls are sloped to direct the entire payload out through the opened gates.
- End Dump: These trucks unload their payload by raising the front end and letting the payload slide down the bottom of the bed and out the back through a tailgate. They are the most popular transport vehicle because they are plentiful, maneuverable and versatile.
- Live Bottom or Flo-Boy: Live bottom dump trucks have a conveyor system at the bottom of their bed to unload their payload. Hot Mix Asphalt is discharged out the back of the bed without raising the bed. Live bottom trucks are more expensive to use and maintain because of the conveyor system but they also reduce segregation problems and can eliminate some detrimental types of truck bed – paver contact.
- Material Transfer Vehicles (MTV): are used to assist the paver in accepting the Hot Mix Asphalt. Most pavers are equipped to receive HMA directly from end dump or live bottom trucks, however, in certain situations it can be necessary to use an MTV. MTVs can minimize truck waiting time at the paving site and may minimize aggregate segregation and temperature differentials.
Asphalt Pavers: The asphalt paver is a self-propelled formless laydown machine with a floating screed. Hot Mix Asphalt is loaded in the front, carried to the rear by a set of flight feeders, spread out by a set of augers, then leveled and compacted by a screed. This set of functions can be divided into two main systems:
- Tractor: The tractor contains the material feed system, which accepts the HMA at the front of the paver, moves it to the rear and spreads it out to the desired width in preparation for screed leveling and compaction.
- Screed: The most critical feature of the paver is the self-leveling screed unit, which determines the profile of the HMA being placed. The screed takes the head of the HMA from the material delivery system, strikes if off at the correct thickness and provides initial mat compaction.
The screed helps control the amount of material extruded onto the base course, flattening the asphalt on the ground. It also assists in offering a level of surface for compaction regardless of the condition of the base course. The base course needs to be reasonably level in an effort to prevent future cracking.
Compactors/Rollers: There are three basic pieces of equipment available for HMA compaction: the paver screed, the steel wheeled roller and the pneumatic tire roller. Each piece of equipment compacts the HMA by two principal means:
- By applying its weight to the HMA surface and compressing the material underneath the ground contact area. Since this compression will be greater for longer periods of contact, lower equipment speeds will produce more compaction. Obviously, higher equipment weight will also increase compression.
- By creating a shear stress between the compressed material underneath the ground contact area and the adjacent uncompressed material. When combined with equipment speed, this produces shear rate. Lowering equipment speed can decrease the shear rate, which increases the shearing stress. Higher shearing stresses are more capable of rearranging aggregate into denser configurations.
Of course, depending on the job, other equipment may be necessary to use when asphalt paving. These machines listed above are the essential pieces of equipment used to pave highways, parking lots and other paved areas. If you have any questions about the paving process, please visit our website for more information or contact our office to speak to a paving specialist.