Asphalt plants continue to face challenges as new regulations are created. Whether faced with air quality requirements or noise reduction options, asphalt plants must continue to make the appropriate upgrades to meet regulations. Gallagher Asphalt Corporation is one company that has successfully enhanced its facilities to meet the growing requirements.
Currently, Gallagher is in its third generation of ownership and was founded in 1928 by James Gallagher. It operates three plants in Illinois located in Thornton, Joliet and Bourbonnais. Thornton is the headquarters of the operation, and it is located on one of the largest limestone quarries in the country.
With the three plants, Gallagher’s largest customer is its own paving crews with up to six or seven crews working at any given time. “We also sell to various other contractors doing paving work from large parking lots to single driveways,” says Jim Trost, vice president of operations.
The customers of Gallagher Asphalt include Illinois Department of Transportation, Chicago Department of Transportation, Illinois Tollway, Cook County, Will County and several local municipalities and government agencies. Gallagher Asphalt also serves the private paving market working for developers or other general contractors.
Before the downturn in the economy, Gallagher was producing an average of about 800,000 tons of hot mix asphalt (HMA) per paving season, with a few seasons peaking around the one million ton mark. In 2011 the plants produced right around 500,000 tons.
The majority of mixes the Gallagher plants produce are standard 30, 50, 70 and 90 gyration Superpave mixes with reclaimed asphalt pavement (RAP), but they also produce recycled asphalt shingles (RAS) and warm mix asphalt (WMA) mixes.
“RAP is used in over 95 percent of the mixes we produce,” Trost says. “About 20 percent of the mix produced contains RAP and RAS, but that number is growing.” The amount of mix incorporating WMA is also growing, and Gallagher has completed two projects using WMA additives.
“We’ve seen very good results from the WMA mixes we’ve produced and tested with the Hamburg wheel rut testing equipment,” Trost says. “Two of the three plants are equipped with WMA foaming capability. Gallagher’s Thornton plant is a Gencor plant and uses the Gencor foaming system and the Joliet facility utilizes an Astec Green foam system.”
Gallgaher’s plants have also received upgrades for a better fines control in the HMA mixtures. “Fines control has been a big issue in Illinois,” Trost says. “To control our mix fines we are required to have a Positive Dust Control System (PDCS).”
In Illinois, HMA plants must weigh the material coming out of the bag house cleaning system, divert it into a storage silo and then feed the prescribed amount of fines back into the mixing drum.
Many HMA plants simply return the bag house fines directly to the mixing drum instead of this type of PDCS.
“Bag house cleaning systems don’t discharge material at a constant flow rate,” Trost says. “We proved this to ourselves by tracking the flow rate of the bag house fines being discharged from the cleaning system over several cycles of cleaning. Different areas in the bag house get loaded heavier than others, resulting in the variation of fines flow during a cycle. Inconsistency of virgin aggregate fines can also affect the amount of fines collected. Startup, transition and shutdown procedures can also add to the variation in mixture fines.”
According to Trost, Gallagher weighs the fines discharged from the bag house in a weighpod, a collection vessel supported on loadcells. “Then, materials are pneumatically conveyed to a storage silo. Our control system corrects for the material removed. Under the fines storage silo we have another weighpod and variable speed vane feeder to allow us to meter a consistent flow of fines back into the mix. The correct amount of fines to meter in is determined by our mix designs and quality control test results,” Trost says.