Time, as the saying goes, is money. On a hot mix asphalt (HMA) paving project, time — more specifically, delays — can be money lost due to failure of the mix, the compaction, and compromised project integrity.
Because of that, a typical HMA job site is organized so each crew member plays a crucial role in producing a smooth, precisely compacted surface. From delivery of the HMA to finish rolling, each asphalt paving project has a choreographed sequence of responsibilities.
Because the time available for compaction (TAC) can be as little as 10 minutes, the role of each crew member is vital to a successful HMA project.
Here are the main crew positions on a typical HMA project:
The truck driver gets the HMA from the mixing drum to the paving operation efficiently, which takes more than just driving. The driver must first load the truck, making sure to use at least three placements to ensure a homogenous mass and avoid segregation of the asphalt mix.
Once on the paving site, the driver backs the truck into position and aligns it with the material transfer vehicle (MTV), paver or windrow. As the paver or MTV moves forward and makes contact with the truck or trailer tires, the truck driver opens the truck's tailgate and dumps the mix. He then follows instructions from the dump person, the paver operator or the MTV operator as he skillfully inches his truck forward in sync with the equipment behind him.
When the load has been delivered, the truck driver pulls away, cleans any residue from the vehicle, and returns to the plant for another load.
In addition to watching for possible safety hazards such as overhead power lines or obstructions, the dump person directs the truck into proper position for discharging HMA into an MTV or a paver, or onto grade for a windrow.
He or she tells the truck driver important information, such as when to change truck bed position, mix discharge rate, and any other information that helps prevent segregation. He or she also tells the driver when to pull away.
When asphalt mix is being unloaded directly into a paver, the dump person makes sure the level in the hopper stays above the minimum limit — typically at least one-third full. The dump person also uses an infrared thermometer to make sure the mix temperature is uniform.
The MTV operator receives HMA from the haul trucks into the MTV, then transfers it to the paver.
The MTV operator communicates with the paver operator, truck driver and dump person to make sure the MTV is in the best position for feeding a continuous, uniform flow of HMA into the paver and that the paving train is moving at a steady speed.
During placement, the paver operator communicates with the truck driver, MTV operator (or dump person) and the screed operator to ensure the paver stays at a speed that balances mix delivery, lay-down capacity and compaction.
He or she keeps the paver moving at a steady speed, avoiding extended stops. He or she must steer the paver smoothly and maintain the reference line to achieve the optimal panel edges and transitions.
If the paver is stopped and started again during placement, the operator should do it smoothly and quickly to avoid surface irregularity or roughness.
Screed operation is vital to successful paving. The operator must understand all the functions and operating characteristics of the type of screed being used (for example, free-floating or self-leveling) in order to produce high-quality longitudinal and transverse joints.
He or she must also be aware of HMA mix characteristics and their effects on the paving process. As the mix is being placed, the screed operator continually monitors the texture of the paving surface and, if necessary, adjusts the screed to ensure the desired mat texture. He or she communicates continuously with the paver operator to maintain a uniform head of material within a 1-inch (25-millimeter) tolerance.
Once HMA is placed, the breakdown compactor operator achieves the specified pavement density within the TAC by rolling over the mix at the proper temperature for air void reduction without risk of damaging the aggregate. This is accomplished, in part, by using an infrared sensor to monitor pavement surface temperature.
The operator maintains an appropriate distance behind the paver, follows a pre-established rolling pattern, and makes the correct number of passes to achieve uniform pavement density and remove marks from its surface.
Finish rolling removes all surface blemishes and other marks created by breakdown and intermediate compacting. It's also performed when breakdown and intermediate rolling fail to achieve target density within the TAC.
No paving operation is complete without an attentive ground crew.
Their job is to make sure the HMA pavement surface is ready for compaction. Using lutes, rakes and shovels, the crew will clean up any spillage between the truck, the MTV, and the paver.
They watch the pavement closely, remove any chunks or foreign material, and hand-work any area where the screed can't place the mix properly.
The ground crew also helps prepare equipment for operation before a shift and clean it afterward.
Although some crew positions on an HMA paving team require more skill, experience and training, every member plays a vital role. By clearly understanding individual responsibilities, being diligent during the shift, and communicating well, the crew will be better prepared for a successful project.
Content provide by Volvo Construction Equipment