Improving mat quality
A continuous paving process also reduces segregation and improves mat quality. "Deviations in ride often occur when the paving speed stops. Optimum uniformity is dependent upon a consistent paving speed," says Rieken.
In the stop-start paving process associated without using the MTD, the screed has a chance to "settle" into the fresh mat while waiting for the next truck. This affects final ride quality of the mat and makes it more difficult to meet the smoothness incentives built into some contracts.
Additionally, contractors will, at times, notice segregated mix coming from the end of the load delivered by the truck. This "load-end" segregation is visible in the mat and cyclically gives evidence of each time the paver has to stop and wait for the next truck. This lack of mix uniformity makes it much more difficult for the roller to meet spec densities in this section of the mat, affecting mat quality.
The paving crew from Iron Mountain, MI contractor, Bacco Construction, noticed these signs of "load-end" segregation on a 75,000-ton U.S. Highway 2 paving application. Before adding an MTD to the paving train, they could see some segregated material in the Superpave 5E3 mix design at the points where the paver had to stop and wait for the next truck.
According to John Fortier, president of Bacco Construction, "We rented the MS-4 for the additional hopper surge capacity to eliminate 'load-end' segregation and to establish continuous paving." After adding the MTD to the paving train, the crew reported that the signs of "load-end" segregation had disappeared. "The transfer device gave us a smoother, higher quality mat with a more uniform aggregate mixture throughout (the mat)," continues Fortier.
Re-blending the material
A re-blending action to the asphalt mixture is accomplished through a variety of methods, depending on the model of MTD used. With the Cedarapids MS-4, large-pitch augers located in the machine's receiving hopper re-blends and channels the material to its delivery elevator.
An additional step of material re-blending also occurs when the contractor adds an insert to the paver's hopper. The size of the insert increases the hopper's surge capacity while the shape channels asphalt directly the paver's delivery system — whether traditional slat conveyor or Remix auger — eliminating the opportunity for the larger aggregate to pool in the hopper wings.
"It's crucial to include a hopper insert when using a transfer device. The live bottom action associated with an insert creates a natural re-blending of the asphalt and increases surge capacity to aid in the continuous paving process," comments Rieken. According to Fortier, the re-blending action also reduces thermal segregation, which makes the asphalt mat much easier to compact to spec densities.
Whether looking to improve trucking efficiencies, increase production or lay a higher quality, more uniform mat, paving contractors should consider the addition of a material transfer device to the paving train.