from On the Move, Fall (September) Quarter 1998, Volume 11, Number 3
Go back to "The Utah Technology Transfer Center On the Move Fall 1998 Newsletter"
Within Utah and many western states, distress in the form of transverse thermal cracking or
rutting frequently occurs in asphalt pavements within three years of initial construction. This type
of distress, if left unchecked, results in premature pavement failure. Over the years the Utah DOT
and most Utah cities and towns have undertaken extensive and expensive crack sealing and chip
sealing programs to mitigate the loss of pavement service life due to thermal cracking. Rutting
distress has also required extensive rehabilitation through roto-milling and replacement of the
asphalt pavement.
The Strategic Highway Research Program (SHRP) launched in 1988 undertook an effort to solve
these premature distresses which resulted in the improved asphalt mix design system known as
Super-Pave. This system calls for the use of performance graded (PG) asphalt cements, improved
aggregate properties and gradations, and a volumetric asphalt mix design procedure. In 1995, the
Utah DOT pro-actively chose to play a leading state role in the implementation and use of the
Super-Pave system. Substantial cost savings, along with improved service levels, is expected to
accrue as a result of this initiative.
Following the lead of UDOT, the engineer staff of Ogden and Orem cities elected to make early
use of the Super-Pave system to extend and improve the service life of their asphalt pavement
streets. In 1996 Ogden City specified the use of the first PG asphalt (PG 64-28) in the
reconstruction of one of their streets. Orem followed suit in 1997, specifying a PG 64-34 asphalt
and improved aggregate properties and gradations along with the full Level I mix design
procedures. Both Ogden and Orem chose to expand their use of Super-Pave this construction
season.
Garco Testing Laboratories performed the mix design using criteria based on a 20-year pavement
design to accommodate 1-3 million 18 kip equivalent single axle loads (ESAL). Optimum asphalt
content for the mix was established at 5.07 percent. Asphalt mix design verification testing by
UDOT during production showed the mix to be within tolerance limits. Petrosource supplied the
PG 64-28 asphalt cement used in the mix. Jack B. Parsons Company is performing the
rehabilitation work. Contract unit bid prices are: roto-milling at $0.90 per square yard; paving
fabric at $0.60 per square yard; and hot mix asphalt at $25.58 ton.
A pre-paving conference was held with the contractor to preview the proposed construction
schedule and paving procedures. Super-Pave mixes, as with other asphalt mixes, must be
compacted to specified density to achieve optimal performance. A compaction test strip was
constructed to determine the proper rolling pattern and compaction effort required to meet
specification density requirements for the project. Super-Pave mixes typically require that rolling
be accomplished immediately after placement and within a specified temperature range.
For the Ogden project, the mixing temperature was set at 320 degrees F with the compaction
temperature set at 296 degrees F. Typically, Super-Pave asphalt mixes require additional
compaction effort due to their improved aggregate structure (and the use of polymers in the
asphalt cement) to meet the specified temperature requirements. In addition, there appears to be a
temperature range between 235265 degrees F where the mix does not compact well, therefore
specified density requirements must be achieved before the mix cools below 265 degrees F.
Finish rolling, however, can be done below 235 degrees F. This phenomenon was experienced on
the Ogden project.
This construction season Orem City reconstructed Orem Boulevard from 400 North to 400
South. This project involved in-place recycling of six inches of the existing surface and placing in
two lifts a total of 5 inches of Super-Pave asphalt mix . A PG 64-34 asphalt cement and a ¾ inch
maximum six aggregate were again specified. Garco Testing Laboratory performed the mix
design and established the asphalt content at 5.1 percent and Geneva Rock did the work.. Some
gradation quality control problems were encountered during construction which affected density.
Once these were corrected, specified density requirements were obtained.
Inspections during the construction of these Super-Pave projects showed no extraordinary
problems in handling, placing and compacting provided the compaction was accomplished within
the proper temperature range. In fact, the Ogden City Super-Pave mix handled especially well
during placement and the contractor did an excellent job in constructing the longitudinal joints.
Field review of completed work shows good to excellent results to date. These projects will be
monitored by the Utah T² Center for the next several years to measure and document the benefits
of the Super-Pave mixes.
The cities of Ogden and Orem, their respective engineering construction staffs, along with the contractors, Jack B. Parsons Company and Geneva Rock, are to be collectively commended on their initiative and innovative efforts to use Super-Pave asphalt mixes to improve the service life of local roads and streets. In addition, UDOT Central Office Materials staff and UDOT Region One Materials staff are to be commended on their excellent technical and laboratory assistance provided to these projects.