The new plant was put into operation last December, and the first warm mix test was to pave at the plant site. The producer used an S1 mix, similar to a 12.5 mm Level C design, with 25% RAP content.
The plant produced both hot and warm mix versions of the mix. "It was very easy to make the switch from hot to warm mix, and the only visual difference was the lack of smoke with the warm mix," mentions Thaw.
The notable differences were in the fuel and asphalt usage. The plant operator ran the warm mix asphalt at 265 degrees F - compared to 315 degrees F as hot mix - and burner positioning dropped from 55 to 40 percent. Thaw estimates a savings of 0.8 gal per ton of fuel oil and 0.2 to 0.3% lower AC content in the warm mix.
The paving crews noticed significant differences in warm mix asphalt workability. While finish rolling of the hot mix design averaged 180 degrees F, the warm mix asphalt remained workable to an impressive 145 degrees F.