While the actual number of "Superpave miles" in Wisconsin's roadway
system is low-approximately 4 to 5 miles-it has made an impression that
greatly exceeds its physical presence. Tom Brokaw, asphalt, aggregate and
soils engineer at the Wisconsin DOT, says the department has been very happy
with Superpave.
"On the test sections we have put down, the data shows that the Superpave
sections had no rutting problems, displayed only 20% reflective cracking-versus
55% on our conventional pavements-and a lower distress index than conventional
pavements," he explains, adding that the winter of '93p;'94 was
a very cold one for Wisconsin, so the sections put down in 1992 were put
to the test.
"We don't see any problems," Brokaw says. "It looks to be
a good package SHRP has put together-the problem is educating people as
to what Superpave is. A lot of people see that it can only be a coarse mix,
but we can even see that there are finer mixes that will meet the Superpave
guidelines. There's a lot more flexibility in the guidelines than some people
think."
While Brokaw say he does not see any drawbacks to the system, he does express
uncertainty about the gyratory compactor used to design Superpave mixes.
"The main difference between Superpave and conventional mixes is the
method of compaction, and the gyratory compactor costs around $28,000. And
the field use of the gyratory compactor is going to be a hang-up; we are
not sure what the specs for field use are going to be. That is one of the
reasons we are going a little slow on this."
Despite this reservation, the few miles of Superpave mix Wisconsin has put
down have impressed the DOT so much that they hope to add some additional
Superpave miles this year, most likely on a "change bid" system
where the contractor requests the switch to this type of mix. In addition,
Brokaw says the department is considering accepting bids with Superpave
mixes for projects put out for bid this year.
