by Jorge Sousa, Ph.D.

Jorge Sousa admires a completed section of A-R pavement.
Below is a look at the blending section of the hot mix plant near Porto
and the paving work on two-lane carriageway in Northern Portugal.

RECIPAV, a new international RPA member, in partnership with International Surfacing Systems (ISS), recently finished a gap-graded Asphalt-Rubber hot mix in northern Portugal. The 30-km dual lane carriage way is under the control of the Portuguese Road Administration, which approved the project after investigating the superior qualities of A-R with respect to longevity, crack retardation, noise reduction, and the beneficial environmental consequences of recycling tires.The project originally called for use of standard asphalt concrete over a fabric interlayer. Consulpav investigated the site using Falling Weight Deflectomer (FWD) readings, core samples, and international roughness indexes to determine the proper A-R mix and thickness needed for equivalency to the original design.
During the mix design process, Repetitive Simple Shear Test at constant height and four-point Flexural Fatigue Tests were performed. The results indicated that A-R hot mix has about 10 times better fatigue resistance than conventional dense-graded mixes while the rut resistance was identical.


The formulation of the Asphalt-Rubber, as well as that of gap-graded mix, strictly follows the recommendations of the ArizonaDepartment of Transportation.
Using the Caltrans design guidelines, the overlay thickness was reduced in half based on a comprehensive mechanistic analysis performed by Consulpav, which included FWD evaluations. The Road Administration also decided to further reduce the overlay thickness in some sections to identify the full potential of this material.
The savings with the new design due to reduced thickness equivalency were shared by Recipav and the contractor.
The necessary mixing equipment manufactured by ISS was imported from the U.S. It was set up by Paulo Fonseca, Recipav general manager with the help of Jeff Smith and John Deere of ISS at a 250 ton-per-hour Ermont drum mix plant north of Porto.
Work began with the placement of test sections for the highway department in late August. The main project began on Hwy. 104 in September. This highway is a primary two-lane carriageway used by both personal vehicles and heavy trucks with an average daily axle equivalent loading of 350 ESALS (130 kN) per lane.

The overall thickness varied between 4 to 6 cm (1.5 - 2.25") and the material placed corresponds to about 1750 metric tons of A-R hot mix. Due to weather, the project completion is delayed until spring, 2000.

Jeffrey Reed, president of ISS and an RPA officer, visited the site in September and said the material placed identically to standard asphalt mixes with neither the crew nor adjacent populations aware that A-R was being placed. After the roads were reopened, a substantial noise reduction was noticed.

Preliminary results indicate that the British Pendulum Friction Test resulted in friction values 25% better than those from adjacent segments of pavement.

Recipav and ISS are working on five other projects and see the expanded use of A-R binders as the future of asphalt concrete paving. They provide greater life at reduced thickness, substantially reduce noise and hydroplaning, and are environmentally and politically correct.