These vehicles also offer large storage capacities to give contractors the necessary material surge to pave continuously at higher speeds, allowing more tons to be laid. Upper and lower paver hopper inserts can be used in conjunction with MTVs, offering more mix storage for the paving train.
Since these vehicles are powered independently of the paver, however, they will have a higher initial purchase price than the MTDs. Crews will need a second operator for the MTV and there are more moving parts than with an MTD, so operating costs will be higher as well.
The large storage capacity helps with continuous paving, but it makes the vehicle heavier. Some MTVs have wheel loads in excess of 100 psi, so they will not be used on all paving lifts, only the top lifts. Due to the higher wheel loads, some state specifications, such as Georgia's, require MTVs to be empty before crossing bridges, while MTV usage in Iowa is dependent upon approval of the project's engineer.
One additional challenge when using some MTVs is adjusting to temperature loss. Longer dwell times in storage bins can result in up to a 60 degree F (33 degree C) temperature loss the first couple of loads, which could drop the mix below specified minimum paving temperatures.
Material transfer devices and vehicles have allowed contractors to make great strides in improving mat quality, while increasing the amount of mix being laid daily. These machines combat segregation and establish continuous paving, which results in smoother mats.
However, adding one of these machines to the paving train does not guarantee a quality final product. "The equipment does not eliminate the need for crews to follow proper paving techniques," offers Rieken. Newcomb agrees, adding, "Segregation with larger aggregate mixes has always been a problem when they are handled improperly."
If the crews are properly trained on the equipment they operate, don't outrun the plant's production capacities and follow quality paving practices, they can achieve bonus-level mat quality more efficiently through the addition of an MTV or MTD.