Plastic type #4 (low-density polyethylene) and #6 (polystyrene or styrofoam) were collected by Target for the mix. Last October, Kansas Asphalt installed 2,800 tons of asphalt with the design mix provided by Granite Construction. The mix was made with reclaimed asphalt pavement as well as 2,200 of the store’s recycled plastic bags and 1,200 plastic bottles. Granite incorporated these plastics via a wet process method at a mixing plant. 

Test lot used 900 cu yd of waste; Granite plans to improve the product.
Photo courtesy Kansas Asphalt Inc.

The plastic was used as part of the bonding agent in the liquid asphalt, with post-consumer products totaling 10% of the binder, according to Kansas Asphalt. 
The overall effect of this recycling project prevented 900 cu yd of waste from entering a landfill. 

Longevity was expected to be equivalent to traditional asphalt; data that the Granite team has since collected shows a 17% resistance to cracks and up to 43% improvement to rutting resistance. 

Ten percent of the asphalt in the lot is made up of recyclables. Twenty percent of typical virgin asphalt can be replaced with the mixture Granite developed for Target. Granite expects the amount of  recycled plastics used in this asphalt to displace up to 200 barrels of oil. 

Granite’s team aims to minimize the complexities that a new or different type of asphalt could create for contractors, according to Granite’s national asphalt manager Edgard Hitti. “The one step that is added to the production is that the virgin asphalt goes through a blending process with the plastic. But after that, the contractor can lay down the newly forged asphalt as if it were typical pavement.” 

Hitti adds, “A major focus of the project was to make sure we don’t create a trade-off between sustainability and performance that would ultimately defeat the purpose of what we are building here.” 

Two types of plastic are used in the liquid asphalt.
Photo courtesy Kansas Asphalt Inc.

The stakeholders are optimistic at the potential this project offers to meet their sustainability and profit targets. Jeffries notes that “the asphalt is holding up great. There haven’t been any issues outside normal parameters…. Even though this project is in the prototype stage, we at Kansas Asphalt see this as a great opportunity for growth.” 

Following a three- to four-month observation period, the next step will be to expand the reach of the prototype RAP.  Jeffries says his aim is to share the pavement with six of the contractor’s national accounts, while Hitti says Granite will pitch the RAP mix to industry agencies such as the American Public Works Association. 

The teams at Granite and Kansas Asphalt are also striving to increase the proportion that recycled plastics can take up in an asphalt mixture. “In lab experiments, we doubled the amount of plastic in the asphalt, but we still need to replicate it in the real world,” says Hitti. “With that being said, we aim to make this RAP competitive with typical asphalt pavements to provide additional incentives for our clients to become more environmentally friendly.” 

By Megan Guttieri