GTR Project in Mississippi Draws Acclaim from Production and Laydown Personnel
The Mississippi Department of Transportation (MDOT) constructed a 1-mile (1.6-km) asphalt
pavement demonstration project July 21, 2011 on U.S. 49 in Gulfport incorporating a PG 76-22
GTR, which is an asphalt binder modified with ground tire rubber. The project consisted of
placing a 1.5-inch (38-mm) thick maintenance overlay on the existing highway pavement. The
first section of the demonstration project was 14 feet (4.3-m) wide consisting of a 12-foot lane
(3.7-m) with a 2-foot (0.6-m) shoulder. The subsequent section was 12 feet (3.7-m) wide.
MDOT classified it as a demonstration project because they normally would have specified a
PG 76-22 SBS polymer-modified asphalt binder. The objective of using the PG 76-22 GTR is to
determine if it performs as well as a PG 76-22 SBS, thereby, increasing competition among
modified asphalt binder suppliers, and possibly taking advantage of the current lower costs of
binders modified with GTR. An additional advantage to society is that old tires collected in
Mississippi in excess of what can be recycled into markets and products can be sent to landfills
as long as they are shredded. A goal in the U.S. dating back to the 1970s is to reduce the
number and size of landfills in the U.S. and the costs to society associated with them.
Blacklidge Emulsions Inc., headquartered in Gulfport, supplied the PG 76-22 GTR to Huey
Stockstill Inc., which is a highway and street paving construction company headquartered in
Picayune, Mississippi. The mixture produced by Huey Stockstill met MDOT specifications for a
9.5-mm Superpave mixture for high traffic pavements. The target asphalt binder content was
6.2 percent with approximately 11 percent ground tire rubber. Blacklidge Emulsions used
approximately 930 tires to formulate the PG 76-22 GTR. About 1,100 tons (1000 Mg) of mixture
was produced.
During plant production, laydown and compaction, Huey Stockwell’s personnel were asked by
Blacklidge Emulsions for comments and input about their PG 76-22 GTR. The hot-mix plant
operator stated that the PG 76-22 GTR pumped as well as a PG 76-22 SBS and there were no
problems with asphalt binder tank operations. The laydown superintendent stated that the
mixture handled well; the compacted mat had a good appearance, and there were no problems
with attaining the required density. Paving crew members stated that the mixture with the PG
76-22 GTR handled similarly to other mixtures they used on other sections of the highway.
Huey Stockstill Jr., president of the construction company, provided the following comment
about the project, “The PG 76-22 GTR demonstration project went very well and we are excited
about getting it approved by MDOT, and taking advantage of the many benefits of PG 76-22
GTR.”
With the successful completion of construction, MDOT has been monitoring the pavement to
determine its performance.