Paving the way to a cleaner, waste-less future with GTR and porous asphalt

Every year approximately 100 million tons of pavement material is reclaimed and 95 percent is returned to the roads and highways it originated from, making asphalt pavement one of America’s most recycled materials.

Asphalt cement –the material that holds pavement together- can be reactivated through heat. When the asphalt is milled up, it is then taken to a facility where it is crushed into manageable chunks. From there, it’s processed through an asphalt plant and mixed with virgin materials to make new pavement. The quality of the mix incorporating reclaimed material is as good as or even better than pavement made from all-new material.

While this practice has been utilized for decades, paving industry has made great strides in recent years in terms of new kinds of alternative applications such as ground-tire-rubber material (GTR) and porous asphalt, which allows water to more easily drain through the pavement surface.

The rubberized road

According to the Environmental Protection Agency (EPA), the market for ground rubber, also referred to as sized-reduced rubber or crumb rubber, has been growing over the past several years. In the GTR market there are two classes of particle sizes: “ground” rubber, 10 mesh and smaller and “coarse” rubber, larger than 10 mesh, with a maximum size of one-half inch.

Asphalt paving is the largest single market for GTR, consuming an estimated 220 million pounds, or approximately 12 million tires annually. Currently, California and Arizona use the most GTR in highway construction, covering more than 80 percent of roadways. Florida is the next largest user and Michigan is quickly rubberizing its roads.    

“We’re working with more GTR material and the state has funding to use this material to keep tires out of landfills in Michigan,” says Bruce Weiss, president of Pyramid Paving Company, a Michigan-based, full-service asphalt paving contactor. “The Michigan Department of Transportation (MDOT) is even looking at making GTR the standard on certain projects, reimbursing up to 50 percent of the cost of the project if GTR is used. It’s certainly an up-and-coming material in road construction.”

According to the EPA, GTR is blended with asphalt to beneficially modify the properties of the asphalt in highway construction. Size-reduced scrap tire rubber can be used either as part of the asphalt rubber binder, seal coat, cap seal spray or joint and crack sealant, or as an aggregate substitution.

The EPA cites the benefits of using GTR as; longer lasting road surfaces, reduced road maintenance, lower road and traffic noise, shorter breaking distances and cost-effective construction. The EPA also claims the application is being used in greater amounts by state Departments of Transportation.

Arizona and Florida have been leaders in asphalt rubber utilization. Texas and Nebraska are currently using greater amounts of asphalt rubber. South Carolina is also pursuing utilization of asphalt rubber in county and state roads. Other states that have studied and/or used rubberized asphalt include New York and New Mexico.

When it rains, it’s porous

Aside from asphalt-alternatives such as GTR, the pavement industry is also utilizing more porous asphalt, a tool for effectively managing storm water, building safer roads with less standing water and managing the heat-island effect in cities by cooling down the pavement.

According to the National Asphalt Pavement Association (NAPA) rainfall is supposed to sink naturally into soil, filter down through and eventually find its way to streams, ponds and lakes. In urban or other high-population areas, rainfall becomes runoff and can contribute to flooding. Contaminants such as oils and minerals are then washed from surfaces directly into waterways without undergoing the filtration that nature intended.

Due to the “less is more,” open structure of the pavement, porous asphalt allows water to drain through the pavement surface into a stone recharge bed and infiltrate into the ground below. Because of the open structure of the pavement, porous asphalt offers a “cooler” pavement choice. By replenishing water tables and aquifers rather than forcing rainfall into storm sewers, porous asphalt also helps to reduce demands on storm sewer systems.

Not only does porous asphalt allow the natural filtration cycle to occur, the material also proves for a safer roadway by reducing standing rainwater, ice and snow. Porous pavements show significant reduction in the need for deicing and anti-icing practices common in the northern states because snow and ice melt faster on a porous surface.

Whether it’s an asphalt alternative such as GTR or porous application, parking lot, highway and road construction is changing for the better as the industry paves the way to a cleaner, waste-less future.

image: http://www.priasphalt.com/testingandspecifications.aspx?id=753