As a light rain fell from a gray sky on a recent weekday morning, several members of the Union community labored on, unaffected. Their job: to pave a walkway behind Memorial Fieldhouse.
The task presented an exciting opportunity. For the first time, the Union workers were using, outside, a revolutionary, eco-friendly mixture of concrete they developed on campus.
The mixture, pervious rubberized concrete, or PRC, contains aggregate, sand, cement and rubber, and presents a new use for old tires by recycling them. It grew out of a collaborative effort by Professor Ashraf Ghaly and Mechanical Engineering major Andrew Heiser ’09, who began research on their product last summer.
Developing the concrete was difficult, Ghaly said, because of the unique integration of rubber in its ingredients. The biggest challenge “was to come up with an optimum mixture.”
“Rubber decreases the overall strength, but makes the concrete more durable,” Heiser said. “It is therefore a balance of trying to find the correct amount of rubber to obtain for optimal permeability, while also keeping the concrete strong enough for its desired purpose.”
Working with members of Facilities Services, Ghaly and Heiser used three different ratios of the mixture to pave the Fieldhouse walkway. Although every mixture is strong enough to behave like typical concrete, they were seeking the combination that allows for the most permeability.
By using one to two millimeter pieces of rubber, they created a porous concrete that offers many advantages.
“Concrete is always thought of as an impervious material,” Ghaly said. “The concrete we poured is pervious, which allows water to percolate through – thus charging underground aquifers, reducing heat island effect and eliminating the need for drainage accessories.”
And by taking waste tires and granulating them into small pieces, the Union researchers also reduced disposal “in less-than-environmentally-friendly ways,” Heiser said.
Come fall, as part of his senior project, Heiser will examine how PRC responds to both hot and cold conditions. In the future, he hopes to continue working with the concrete and that it will eventually become the norm for paving walkways and driveways.
It is, he believes, a unique way for Union to differentiate itself in its sustainability efforts.
Last summer, the College signed the American College and University Presidents Climate Commitment, which aims to reduce greenhouse gas emissions from campuses. The possible use of its own pervious rubberized concrete would enable the College to “adopt something environmentally friendly.”
Ghaly, a proponent of sustainability as a way of life both on campus and off, said that after a year’s worth of trial and error in the lab, he hopes the PRC project “demonstrates that small and simple ideas are like little seeds that grow and become big trees. These ideas have the potential to make a significant difference in our environment.”
– Shauna Keeler '09