The paving crew is supplied by the department’s own Barber Greene parallel-flow drum plant, which produces approximately 52,000 tons of HMA annually. The department also purchases another 10,000 to 15,000 tons from an independent producer.
The Syracuse street department’s HMA plant produces a basic Marshall Mix, which seems to work best for the drainage and the climatic conditions the streets are exposed to. All binder course mixes used in mill and fill applications consists of ½- to ¾-inch nominal size aggregate and 5.6 percent asphalt cement binder, with 30 percent reclaimed asphalt pavement (RAP) content.
Some of the milled asphalt, like sheet asphalt (sand and asphalt binder) which was commonly used in Syracuse at one time, can’t be used as a RAP additive because it lacks aggregate and produces a high blue smoke emission when added to a mix. As for the surface course applied on Syracuse street projects, the plant produces a similar Marshall Mix with ¼-inch nominal aggregate size.
“It cost us $28 per ton to produce the mix we need and under a government contract with an independent producer it would cost us $32 to $33 per ton,” Wright says. “So, we not only save quite a bit by producing our own mix, we’re also able to easily adjust to what our paving crews need. If we have a lot of utility work that slows us down, we can make that adjustment at our plant instead of telling an independent producer what we think we may or may not need on any given day.”
The savings and control the HMA plant provides Wright’s street department is such a significant benefit that The Bureau of Street Repair is in the process of researching the purchase of a new plant. Currently, the street department is looking at replacing its current 120-tph plant and 50-ton storage silo with a 250-tph plant and two 100-ton silo system.