UA Researcher Combines Recycling and Construction

TUSCALOOSA, Ala. – In the last 10 years, the nation has seen a surge in household recycling. Communities across the country are collecting tons of recycled material everyday. This trend led Dr. Andrew Graettinger, an assistant professor of civil and environmental engineering at The University of Alabama, to develop a new lightweight fill made of recycled plastic bottles.

Traditionally, soil fills the space behind retaining walls, such as those built for interstate highway dividers and sound barriers. Soil is extremely heavy and exerts a lot of pressure against the retaining wall. Over time, the wall can lean or crack because of the pressure.

The plastic bottle blocks would be used in replacing soil behind interstate highway retaining walls. The blocks would be covered with some soil and grass for aesthetic purposes.

“The plastic bottle blocks weigh considerably less than soil,” said Graettinger. “For construction applications, the lighter-weight plastic bottle fill is easier to handle and will save money because the retaining wall does not have to be as strong.”

The plastic bottle blocks are approximately 2-feet high by 2-feet wide by 2-feet deep and contain 150-200 plastic bottles. Urethane foam holds the bottles together in the square block form. The 4-square-foot bottle block can withstand up to 2 tons of weight.

The blocks weigh approximately 2 pounds/cubic foot compared to soil which weighs approximately 110 pounds/cubic foot. “This means that five stories of plastic bottle fill weigh the same as one foot of soil,” explained Graettinger.

Graettinger was awarded a research grant from the University for this project. He also received new plastic bottles from the Coca-Cola Co. to help with initial testing by forming a control group of bottle blocks that were made with all of the same type of bottle.

“We have started making blocks out of recycled bottles and have seen no difference in weight and strength testing,” continued Graettinger. “It is exciting to work on a project that solves an engineering problem and provides a new environmental recycling initiative.”

In 1837, UA became the first university in the state to offer engineering classes and was one of the first five in the nation to do so. Today, the College of Engineering, with about 1,900 students and more than 90 faculty, is one of the three oldest continuously operating engineering programs in the country and has been fully accredited since accreditation standards were implemented in the 1930s.