COVID-19 Information
Dartmouth Engineer - The Magazine of Thayer School of EngineeringDartmouth Engineer - The Magazine of Thayer School of Engineering

Paving the Way to Recycled Roads

Jeffrey Melton Th’99 Drives the Nation Toward Sustainable Highways.

By Adrienne Mongan


Gas mileage is a concern of millions of Americans who drive along the country’s highways. But when Jeffrey Melton Th’99 takes his vehicle out on the road, he’s actually thinking about the road.

As director of outreach at the national Recycled Materials Resource Center (RMRC), Melton is on the road a lot to promote sustainable highway engineering, including building roads with materials otherwise destined for landfills.

Established in 1998, at the University of New Hampshire, the federally funded RMRC partners the Federal Highway Administration with UNH to address the difficult task of continuing highway expansion without further depleting vital resources. Working with numerous state departments of transportation (DOTs) and environmental regulatory agencies (ERAs), Melton advocates for big changes in the highway landscape.

We are all familiar with today’s main roadway material. Asphalt is everywhere: thousands of miles of roads and highways are paved with it. Most Americans are not aware that asphalt is a byproduct of crude oil — with the same limited road ahead. “In a couple of decades, we’ll see a shortage of asphalt,” Melton says. “People are already stealing asphalt from roads and using it in construction projects.”

Jeff Melton pictured at a test site at the Recycled Materials Resource Center at the University of New Hampshire
ROAD WARRIOR: "The green highway movement is where green building was 20 years ago," says Jeff Melton pictured at a test site at the Recycled Materials Resource Center at the University of New Hampshire. Photograph courtesy of Recycled Materials Resource Center.

The RMRC’s goal of encouraging the use of recycled materials is a formidable one, considering that approximately 11 billion tons of industrial waste is generated each year in the United States. If some of this material could be used in highway construction, it would decrease the volume of these materials entering landfills and help preserve the natural resources used in building highways. This is where Melton and the issue of sustainability enter the picture. In its most basic form, sustainable engineering incorporates design, materials, and procedures that result in a cost-effective, quality product while at the same time minimizing the environmental impact and risks to human health associated with the engineering process. In describing the sustainable engineering approach, Melton says, “Our goal for highway expansion and restoration projects is to achieve them in a manner that minimizes the amount of new material used, the amount of energy used in material production and project construction while at the same time working to minimize the amount of greenhouse gas generated.”

Despite its clear environmental benefits, a purist might argue that the RMRC’s efforts are not reflective of true sustainable engineering because the center promotes a mode of transportation that is not sustainable. Addressing this dilemma, Melton states, “We take a pragmatic approach and acknowledge that people are not going to give up driving anytime soon. Highways are going to be built regardless, so why not try and construct them in the most sustainable, environmentally friendly way possible?”

Approximately 350 million tons of natural and manufactured materials are used in highway construction each year. In addition, an estimated 350 to 850 million tons of byproduct and secondary-use materials are generated each year in the United States. These secondary-use materials include tires, asphalt shingles, crushed concrete, reclaimed asphalt pavement, coal combustion products, foundry sands, and slags. Implementing these secondary-use materials in road construction allows engineers to conserve high-quality virgin materials while finding a value application for materials that might otherwise go into a landfill. Given this, the question that engineers using the sustainability application face when working on projects becomes: “Can I take a material that in the past has been viewed as a waste and make it into something of value either as a construction or fill material?” says Melton.

At the RMRC, researchers are challenged on a daily basis to test, evaluate, and develop guidelines and specifications for new and familiar materials for use in the highway environment. The center works through outreach and research projects to, as Melton says, “overcome barriers to the appropriate use of recycled materials in the highway environment.” Among the areas studied at the center and an example of recycling in action is the use of recycled concrete. Concrete is one of the most recycled materials used in highways, because of its abundance and high quality as an aggregate source. In fact, estimates indicate that building demolition in the United States generates approximately 123 million tons of waste per year and helps create recycled concrete. After a cleaning process that removes unwanted materials such as brick, steel, and glass, the material is crushed. Once this process is completed, electromagnets remove any residual metal and the remaining recycled product is used as recycled concrete aggregate (RCA).

One of the initiatives of the RMRC is to help promote the use of RCA to state DOTs that are not currently using it. As a part of its action plan, the RMRC is conducting a performance survey of the pavements in high RCA-usage states such as Idaho, Minnesota, and Wyoming as well as obtaining field samples for physical, chemical, and petrographic evaluation. The data obtained will be used to help develop guidelines for the expected performance of pavement made of RCA concrete and will be disseminated to all state DOTs, with the hopes of increasing the use of this plentiful recycled material.

The pay-offs can be substantial in several realms. “By increasing our recycling efforts today, we will undoubtedly reduce any adverse environmental impacts in the future,” Melton says. “So in terms of the big picture, the benefits of recycling go beyond the environment and include significant economic ones as well.” Researchers at Penn State, for example, credit concrete mixtures — using byproducts such as fly ash, silica fume, ground granulated blast furnace slag, and an alkaline earth mineral mixture—with helping to lengthen lifespans of bridge decks. The added materials reduce the permeability of concrete, deter salt from entering concrete, and increase electrical resistance. By using these byproducts in bridge deck construction, which significantly increases the lifespan of such structures and also helps slow corrosion, researchers in Pennsylvania estimate cost savings could reach more than $35 million annually.

But there are still roadblocks to using recycled materials for highways. One of the most significant barriers Melton focuses on is separating legitimate concerns about recyclables from general negativity associated with materials defined as waste. “The potential for leaching dangerous materials is always a concern, both from environmental and human health perspectives” he says. “People in favor of recycling need to have the data to prove that a given material does not pose a risk in a given application.” Getting the right information to the right people is key. With communication between all the parties involved, whether between the state DOTs and state EPAs or between one of these agencies and individual community members, the chances of a project getting the green light are much higher. “People want to be involved in the process from the beginning,” says Melton. “They do not want to be surprised. Even though they may be very receptive to using recycled materials, they want to understand the project parameters, why this material is being considered, and all the data collected on it.”

FIXING A BROKEN LAWNMOWER WAS THE SPARK THAT IGNITED Jeff Melton’s interest in engineering. “I became fascinated with how things work, why they break, and how to fix them,” Melton explains. After graduating from Hamilton College in 1991 with a B.A. in physics and then from UNH in 1994 with a M.S. in ocean engineering, Melton entered Thayer, where he earned a Ph.D. in engineering sciences in 1999. After graduating from Thayer, Melton joined the U.S. Army Corps of Engineers, working as a research hydraulic engineer. While serving as a member of the dredging team, working on sediment management, Melton’s interest in contaminated sediment and recycled materials began to develop. In working with the team to determine ways to use the dredge material in a beneficial manner instead of simply disposing of it, Melton recalls, “I began to think, how can we take a mixture of sand and mud, for instance, and do something of high value with it instead of simply using it as a low-value application.” He adds that the transition to the RMRC was a natural extension of his interest in the beneficial use of waste materials.

Among his current research projects, Melton is working on the characterization of construction and demolition (C&D) debris found in New Hampshire. “Because we build so much with granite here, we have a lot of it mixed with concrete and brick available. But because we do not know how this material behaves under certain circumstances, we have not used it. So my challenge is to determine how this C&D material behaves in order to promote its use in the highway environment,” explains Melton.

Looking forward, he believes that the use of recycled materials will only increase. Among the reasons he cites are higher demand for natural resources from developing nations and population growth, most notably in the United States. “As our population grows so will the infrastructure needed to support it,” Melton says. “As a result, available land will become scarce for such things as gravel pits, which hold the aggregate material used in highways, so out of sheer necessity we will have to recycle materials.”

Coming to a Highway Near You

A wide range of recycled materials are already used in roads in the United States or abroad or are being tested for suitability. Here’s a sampling.

Asphalt roofing shingles
Uses: aggregate, asphalt cement modifier, substitute for gravel roads

Blast furnace slag
Uses: hot-mix asphalt, Portland cement concrete, granular base, embankments, fills

Scrap tires
Uses: embankments, retaining walls, aggregate substitute, asphalt modifier

Coal bottom ash/boiler slag
Uses: asphalt concrete aggregate, granular base, stabilized base aggregate, embankment, fills

Foundry sand
Uses: asphalt concrete, flowable fill aggregate

Mining and mineral processing wastes
Uses: asphalt concrete aggregate, granular base, embankments, fill

Municipal waste combustor ash
Uses: aggregate substitute in asphalt paving mixes, fill, embankments

Waste plastics
Uses: soil stabilizing pins, aggregates

Reclaimed asphalt pavement
Uses: new pavement

Reclaimed concrete
Uses: aggregate substitute

Sewage sludge ash
Uses: asphalt paving mixes

—Adrienne Mongan is a freelance writer living in Vermont.

For more photos, visit our Energy Technologies and Sustainability Flickr page.

Categories: Features

Tags: alumni, energy, environment

comments powered by Disqus