The participants expressed concerns about: limited storage capacity for both viscosity graded and performance graded asphalts, and the introduction of numerous grades; the limited demand for modified performance graded asphalt binders in other states; the availability and cost of installing equipment and training personnel at every terminal; and the time involved to run the complete set of tests and certify acceptable material before it is shipped.
Furnishing PG 64-22 was not considered to be a problem because it was basically the same asphalt that was already being shipped as an AC-20 or AC-30. Other grades could be modified as needed.
Arkansas is divided into two climate zones, based on SHRP. A review of the proposed grades, based on geographical location and reliability, was made. PG 64-22 would not provide 98% reliability for the entire state, but it would provide 80% or higher reliability in all but a few isolated locations.
A policy was established and Performance Grade binders were implemented on all projects, beginning with the November letting in 1995.
The policy is as follows:
PG 64-22: projects with under 10,000,000 total esals.
PG 70-22: projects with over 10,000,000 total esals and under 30,000,000 total esals; projects with over 1,000,000 total esals with slow-moving traffic (<30 mph).
PG 76-22: projects on the Interstate or routes with over 30,000,000 total esals.
The standard specification that was introduced in November of 1995 for all projects was blind to the type of modification; acceptance was based entirely on the SHRP grading. Since that time, we have received PG 76-22 and PG 70-22 binder that has been modified with an SBX at a refinery or terminal, and a latex modified that has been blended at the hot mix plant. On one project, we are expecting a PG 76-22 to be modified by air blowing.
AHTD specifications, subsequent to the change to performance grades, had required a minimum of 3% polymer.
Since the introduction of Performance Grade asphalts, we have placed or contracted nearly 500,000 tons of Modified asphalt binder.
A couple of projects that are being constructed will further evaluate these PG binders by requiring a 76-22, 70-22, 64-22, and a 58-22 on the same project, with the only modifier of the asphalt cement being an SBS or SBR. These two projects are being constructed using the full Superpave design.
The Department has three projects that have used or are using the Superpave mix design procedures:
A job on Interstate 30 called for patching and overlay work using ACHM Type Heavy Traffic (HT) mix with PG 76-22 binder. The job starts at the Texas state line in Texarkana and runs east for a distance of 7 miles. The typical section called for two thin lifts of binder course (total 3 or 4 1/2 inches) and a wearing course of 1 1/2. A Special Provision required that each lift must be completed over the entire roadway before the next lift could be started. Also, the contract called for the easternmost area (approx. 4 miles) to be completed first. By the time the Superpave mixes had been designed, almost all of the first lift of binder had been placed over the first 4-mile section. Thereafter, except for a mile of roadway overlaid with Heavy Traffic mix, the remainder of the project was completed using Superpave designed mixes.
A total of 38,600 tons of binder course and 30,000 tons of surface course, Superpave designed mix were used for the project. There was a cost difference of $0.70/ton for Mineral Aggregate for surface and $2.40/ton for Mineral Aggregate for binder course.
FHWA brought in its mobile field lab for two months last spring and provided a close-out conference in our office in June. The results of their testing provided a comparison to our results and insight concerning differences in sampling and testing procedures. This information will be very useful for quality control and assurance on future projects.
District personnel indicated that the mix looked tough and had not given any indication of any rutting.
The design was based on using 240 gyrations for Nmax.
Pavement core samples were sent to Georgia DOT for loaded wheel testing. The results of the Superpave cores indicated that the amount of rutting for the Superpave was less than the HT and less than the maximum allowed by Georgia for the types of mixes.
Samples were also sent to the University of Arkansas at Fayetteville for Hamburg. Wheel testing and results showed the Superpave mix to perform better than the HT mix.
This job is located at Forrest City and involves the replacement of two sets of bridges on I-40 and the overlaying of the existing PCCP between them with Heavy Traffic hot mix.
A change order called for using 7.192 tons of two lifts of Superpave binder course in lieu of HT binder and 1,322.3 tons of one lift of Superpave surface course in lieu of HT surface. The change to the Superpave cost $1.00/ton of Mineral Aggregate for both surface and binder course. The total cost difference was $14,700 because of the difference in asphalt binder courses contents.
Just recently, another change order was made to replace the rest of the HT mixes with Superpave.
The design was based on using 240 gyrations for Nmax.
Except for initial density problems, there were no particular production or construction problems reported.
This project requires the contractor to perform the design and
quality control on all the hot mix. Only 1354.93 tons of surface
and 2533.08 tons of binder have been laid to date. No production
or construction problems have been reported.
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