Production and Placement of Superpave Hot Mix Asphaltic Concrete Pavement
Recently, our company was awarded a highway contract from the
Texas Department of Transportation on US 271 in Red River County.
This contract consisted primarily of a two-inch hot mix overlay.
Approximately eleven thousand tons of this material consisted
of a 19.0mm Superpave hot mix.
Paving Train: Notice distance of roller in relation
to paver. Essential in placement of Superpave.
Production began on October 30, 1997, using a CMI drum mix plant.
Production, compared with a normal Type C hot mix, was a pleasant
surprise. Although a higher temperature mix, approximatly 35%
less fuel was required to produce this mix. The temperature of
the hot mix during production was 325° F, the maximum allowed by
permit. Segregation of the hot mix during batching did not occur.
Breakdown of MAT.
At the beginning of placement, the air temperature was 53° F and
the conditions were cloudy. The hot mix was produced at a temperature
of 325° F and transported 35 miles to the jobsite. The mix arrived
at the jobsite at 300° F. The mix was dumped directly into a Roadtec
RP-230 paver and breakdown was initially achieved using two Caterpillar
634-C twelve-ton rollers. Temeperature loss after one pass ranged
between 30-40 degrees. Some tenderness in the mix was witnessed
primarily due to the rollers' inability to coordinate the passes
and starting and stopping too quickly. The rolling pattern consisted
of four passes with both drums set in the vibratory mode at the
high amplitude setting. Breakdown was eventually achieved using
one breakdown roller. The second roller was used to remove roller
marks after the mat temperature cooled below 190° F.In conclusion, our experience with superpave hot mix has been very favorable. The superpave hot mix was placed under less than ideal conditions with the temperature a few mornings beginning in the low 40's. Production was much more economic than a normal Type C hot mix. Placement of the superpave was much better than expected. In place air voids for the superpave hot mix averaged 8% and certainly would have been higher if placement had occurred in warmer temperatures. The only surprise with this mix was the rapid temperature loss during placement. Again, our experience with Superpave was so favorable; we asked and received permission from TxDOT to complete this project using Superpave hot mixes.
Completed MAT.
