Improving the Strength and Durability of Pervious Pavement with Recycled Carbon Fibers

Innovations in Environmental Engineering: Improving the Strength and Durability of Pervious Pavement with Recycled Carbon Fibers

Effective urban stormwater management and the disposal of carbon fibers from manufacturers both pose significant environmental challenges. A research team from Washington State University recently announced a cost-effective solution to both issues – blending recycled carbon fibers into pervious the pavement.

Pervious concrete pavements provide a means of decreasing stormwater runoff by allowing it to seep into the group once it flows through a stone substrate. Image Credit: JJ Harrison via Wikimedia Commons

One of the effects of urbanization is the challenge of efficiently and cost-effectively managing stormwater. As developments pave former green spaces, the only place for rainwater to go is up, which, of course, leads to urban flooding. Another environmental issue in need of a solution is what to do with unused carbon fiber composites, a waste product that accounts for 30 percent of the composite material created by wind turbine, car, and airplane manufacturers. Fortunately, an environmentally friendly and cost-effective solution may be at hand. A Washington State University research team, working under the leadership of Karl Englund, Ph.D., Associate Research Professor, Composite Materials, and Engineering Center, recently published their work demonstrating that infusing a pervious concrete mixture with recycled carbon fibers increases the strength and durability of pervious pavement. What are the benefits of pervious pavement? How can this research address the challenge of disposing of both stormwater and carbon fiber composites in an environmentally sensitive manner?

The Environmental Benefits of Pervious Pavement

An illustration depicting the effect of urbanization on stormwater management. Image Credit: Environmental Protection Agency via Wikimedia Commons

As people migrate to cities in increasing numbers, areas that were once green spaces are now being covered with homes, shopping centers, sidewalks, and streets. As a result, urban flooding is on the increase. One solution is the use of pervious pavement that allows rainwater to seep into ground through a substrate that naturally filters out many pollutants.

Some of the other environmental benefits of using pervious pavement in urban settings include the following:

• Minimizes the erosion caused by stormwater runoff in both urban areas and near streams and rivers.
• Decreases the chemical load of urban runoff into lakes and wetlands.
• Improves the recharge of groundwater aquifers
• Protects fisheries from temperature changes caused by heated urban runoff
• Reduces the amount of salt and other chemicals needed for de-icing since the water and ice melt does not stand on the pavement.
• Reduces auto accidents that occur during wet weather.
• Decreases long-term maintenance cost when compared to asphalt.

Despite the numerous and significant benefits of using pervious pavement, its use is limited since current products on the market are not as strong or durable as non pervious concrete, asphalt and other materials.

The Results of Infusing Pervious Concrete with Recycled Carbon Fibers

A sheet of carbon fiber used in composites. Image Credit: Brett Jordan via Flickr

To make their pervious concrete product infused with recycled carbon fibers, the Washington State University research group first milled scrap carbon fiber composite material they sourced from the airplane manufacturer Boeing. The composite included carbon embedded in a matrix of vinyl ester, epoxy, or polyester thermoset. They chose this method since it uses little heat or chemicals, which minimizes cost and environmental impacts. In addition, by keeping the carbon fiber waste material in its original cured form, the team found the maintained the composites strength. Another benefit to this method is that it uses a great deal of the waste material, thus keeping the waste out of the landfill.

Once the team completed the recycling process, they added the carbon fiber composite material to their pervious concrete mixture until it reached four to five percent of the total mix. They ensured the fiber were evenly dispersed through the mixture to create a product with uniform strength.  After the mixture hardened and cured, the group conducted rigorous testing of the product.

Their laboratory testing of the product yielded the following results:

• Overall, the addition of the carbon fibers increased both the strength and durability of the pervious concrete.
• The split tensile strength improved in the infused concrete mixture from 57 percent to 84 percent.
• The modules of rupture improved from 36 to 65 percent in the carbon pervious concrete product.

The research team is now in the planning phase of testing real world applications of their carbon infused pervious concrete material. In addition, they are also working to build a supply chain.

Do you think this pervious concrete product might be a solution to stormwater runoff issues? Why or why not?