The Exeter, Rhode Island, Department of Public Roads recently applied recycled asphalt shingles (RAS) to the gravel surface of a portion of historic New London Turnpike, as part of a series of experiments to determine the most economical way to preserve the town’s numerous gravel roads.

A significant stretch of the Turnpike in Exeter is among the 20 miles of gravel roads serving this community located in the south-central part of Rhode Island. These gravel roads require frequent dressing-up by the DPW’s staff of 18, according to Director Steve Mattscheck. A 35-year veteran of the town’s DPW and its predecessor, the Highway Department, Mattscheck is collaborating with R. Paul Montenegro, Providence-based consultant, to find a cost-effective process to stabilize gravel roads. A specialist in pavement preservation and recycling, Montenegro is guiding the department through several trials to perfect the application of RAS in its maintenance protocol. The centuries-old New London Turnpike is the town’s first gravel road to undergo an RAS trial.

The End of an Era

In the 1800s, the Turnpike was the principal non-coastal stagecoach route between Providence, Rhode Island and New London, Connecticut, making it one of America’s earliest interstate highways. It remained busy until early in the 20th Century when Henry Ford created the automobile assembly line, making cars affordable for the middle class. The horse-and-buggy mode of travel was soon abandoned as the proliferation of automobiles created a demand for improved state and interstate roads – and marked the end of the New London Turnpike as a major interstate route. Today, parts of the New London Turnpike in Rhode Island and Connecticut are located on Interstate 95.

Mattscheck said the Exeter section of the Turnpike currently experiences a low volume of traffic but is still regularly maintained, and is a good candidate for the RAS gravel stabilization experiment. He noted that the results of the trial are expected to help establish a cheaper but more effective protocol for maintaining the town’s gravel roads.

New Ways to Better Roads With RAS

Montenegro indicated the Exeter gravel road stabilization project correlates to an earlier trial of RAS usage in Smithfield, Rhode Island, but differs in that the Exeter trial employs RAS to stabilize a gravel road surface while the Smithfield trial utilized RAS to enhance the aggregate base produced during full-depth reclamation. (See “Smithfield DPW Tests New Use for Recycled Asphalt Shingles") He noted that both Exeter and Smithfield trials depart from current industry practice of adding RAS to hot mix- and warm mix asphalt for pavement applications.

“It’s common in gravel road base stabilization to use some sort of stabilizer, either portland cement or asphalt cement or a combination of both, to bind the fine aggregates together. And whether the asphalt is neat or in an emulsion, it helps to waterproof the road, keeping moisture from intruding into the stone matrix, strengthens the base and stops rutting,” Montenegro pointed out.

He added that RAS usage is a simple cost-effective, clean choice to raise the asphalt content of a road, since the shingles consist of 25 percent asphalt.

“Every 4 tons of shingles applied to a road contribute 1-ton of asphalt. Liquid asphalt is currently $600 per ton, and shingles are about $18 per ton delivered. So 4 tons of RAS costing $72 delivers $600 worth of residual asphalt.  

“Getting the RAS into the gravel surface will differ with each town that tries this. In Exeter, Mattscheck added RAS to his customary procedure using his road sanders at the appropriate stages,” Montenegro explained.

Modified Procedure and Equipment

About 10 tons of RAS used for the Exeter trial were donated by Chris Carney of C. Carney Environmental, Raynham, Massachusetts. Carney produced the material using a CBI Shingle Pro XL 406 Shingle Shredder. Carney had also supplied RAS for the earlier, Smithfield FDR project.

The two-lane stretch of Turnpike undergoing RAS stabilization is approximately 1,500 feet long and 22 feet wide, with much of it laid out on a 3.5 percent grade. One lane was treated while the other continued to carry traffic. Before applying RAS to the road, the DPW used a Volvo G930B Grader to rework the existing surface and re-establish a uniform crown. This process resulted in a windrow of loose gravel material being formed along the center of the road, which they covered with RAS using two 40,000-pound GVW trucks (International and Freightliner) equipped with Tenco side-dumping salt-spreaders. Next, they used the grader to blend the RAS with existing gravel and re-graded the road surface. This procedure was repeated several times until the top of the graded road surface consisted of a 4-inch-deep, approximately 50/50 blend of gravel and RAS. For the last step, the crew placed a 1/4-inch layer of RAS across the entire lane. Traffic was allowed immediately on the completed section of road.

Mattscheck said the operation was expedited by the use of Olofsfors Sharq P-300 blades mounted on the grader’s 12-foot-wide moldboard. The Swedish-made steel blades, which are perforated and have sharp edges, break up compacted gravel without crushing the aggregate, according to Mattscheck.

Adding Asphalt Emulsion Rejuvenator

About one week after the RAS blend was applied to the Turnpike, the second part of the trial took place. This involved the application of a proprietary asphalt emulsion rejuvenator to the road surface by Felix A. Marino Co. Inc. at the rate of 0.25 gallons per square yard using an Etnyre liquid asphalt distributor. The emulsion wet the surface of the RAS, improving cohesion with the gravel particles and further stabilizing the road, according to Montenegro.

The consultant intends to monitor the performance of the treated Turnpike section with DPW Director Mattscheck over the coming seasons. He added that the Exeter DPW will undertake other RAS stabilization trials, including the use of special asphalt emulsions supplied by All States Asphalt Material Group, a “green” (non-toxic) Delta S asphalt rejuvenator developed by Collaborative Aggregates, and Lignin sulfonate-based material supplied by Safe Roads Services.

Brighter Future for RAS Use

The use of recycled materials in asphalt pavements, primarily reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS), conserves raw materials, lowers overall asphalt mixture costs and reduces the stream of material going into landfills, according to the “2017 Asphalt Pavement Industry Survey…” conducted by the National Asphalt Pavement Association. The study, underwritten by the Federal Highway Administration, also notes that the use of RAP far outweighs that of RAS in asphalt mixes, although there is up to 25 percent asphalt in each ton of post-consumer shingles compared to 5- or 6 percent in each ton of RAP.

One of the reasons for this contradiction is that the asphalt in RAP is easier to recover, and less stiff, than the asphalt in highly oxidized shingles. The study also shows that approximately 1.4 million tons of RAS is currently stockpiled in the 50 states – indicating there is a substantial untapped treasure of asphalt in those piles. But while the use of RAS in asphalt pavement mixtures has increased from 701,000 tons in 2009 to an estimated 944,000 tons in 2017, it declined significantly (32 percent) from 2016 to 2017.

There is, however, a development that may help reverse this decline. The NAPA study points out that there appears to be an upward trend in RAS utilization when high quantities of softer binder or recycling agents are employed.

In addition, an upward trend in the use of RAS is expected as increasing numbers of communities, such as Smithfield and Exeter, Rhode Island, try new ways of utilizing the material for maintaining and preserving their local roads.