Director, Strategic Technologies
Successful asphalt paving projects do not happen by accident. They are the result of careful planning and implementation. From restricting or rerouting traffic flow to making sure the right asphalt equipment is on-site to perform the job, a complex series of events comprises an asphalt paving project, especially in the critical asphalt laydown phase.
To achieve the best results and most profitable operation on an asphalt paving project, contractors must balance the elements of hot mix asphalt (HMA) production and placement. A number of hot mix asphalt plants are available. Top-end stationary drum mix facilities produce up to 700 tons (635 metric tons) per hour of HMA. On the other end of the spectrum, portable drum / batch plants produce 30 to more than 100 tons (90 metric tons) per hour of hot mix asphalt.
Paving projects are rarely adjacent to a hot mix asphalt plant, so transportation of the material is necessary. A wide variety of types and sizes of transport vehicles are available, many specifically designed to haul HMA. Live bottom and moving floor trailers feature the largest haul capacities; dump trailers and trucks have less capacity.
Regardless of the type and capacity of the haul vehicles, the delivery of hot mix asphalt from the plant to the asphalt paving project requires consistency and regularity so that the mix being placed is of uniform temperature. Specified density and smoothness of the finished asphalt pavement can only be achieved when the mix temperature is uniform.
Placement of hot mix asphalt is a two-part process. The first portion of placement is laydown, accomplished using an asphalt paver. An asphalt paver has two major components - the tractor and the screed. The tractor is the prime mover that is used for self-propulsion of the asphalt equipment. The screed is the working tool, the equipment that spreads the HMA into asphalt pavement.
The operator must judge three factors when determining paving speed. First, the operator must see how much hot mix asphalt is being delivered to the asphalt paver. Second, the operator must look down at the width and thickness of the asphalt pavement panel being laid.
Third, the operator must check behind the asphalt paver to see if the compactor train is able to keep up with the paver.
This balance between production and placement needs to be maintained throughout asphalt paving. If the delivery of asphalt mix to the paver is interrupted, the asphalt paver needs to stop. Current practice is to rapidly stop and start the paver so the screed level does not fluctuate because of asphalt paving speed or head-of-material in front of the screed. If the paver outruns the compactor train, the entire asphalt paving operation is at risk of failing to achieve target density and/or asphalt pavement smoothness.