Michigan is no stranger to poor roads and decrepit bridges. Crumbling and outdated infrastructure costs threaten to overwhelm even the most fiscally responsible communities across our state. Researchers at the University of Michigan believe they have an answer: a high performing concrete formula to decrease costs while increasing durability and longevity.
Michigan roads and bridges are primarily built with a standard concrete formula. There is a stronger and superior concrete known as Ultra-High Performance Concrete (UHPC) on the market, but for most municipalities it is prohibitively expensive. Existing UHPC blends are proprietary and available through just a handful of companies.
Facing a backlog of hundreds of billions of dollars in needed bridge and road repairs, the Michigan Department of Transportation asked U-M to design and concoct a non-proprietary UHPC formula for public use. Sherif El-Tawil, a professor of civil and environmental engineering, lead a team of engineers on the project.
A key measurement of concrete durability is the number of freeze-thaw cycles it undergoes before noticeable deterioration. Standard concrete is rated at 28 cycles. Michigan’s UHPC blend rates at 90 cycles.
Another important characteristic of concrete is its ability to withstand downward force. UHPC outpaces standard concrete. “Regular concrete will have a strength of about 4,000 pounds per square inch (psi)… that’s maybe the weight of an SUV on every square inch,” said Sherif El-Tawil. “However, UHPC can support at least 22,000 psi or six times as much.”
Standard concrete blends are a mixture of cement, gravel, sand, and water. The UPHC replaces gravel with a variety of carefully selected fine sand particles. The mixture structure is more densely packed than traditional concrete. Increased density means less water finds its way into the concrete therefor reducing damage from expansion as the water freezes. With an eye toward reducing maintenance costs, the researchers included half-inch long steel fibers to add strain-hardening to the concrete. In other words, bend but don’t break.
A municipality may pay between $100-$120 per cubic yard for a standard concrete. For an existing proprietary UPHC blend the cost rises to more than $3000 per cubic yard. U-M states that their blend reduces costs by 70%.
The new concrete is currently in use on a bridge in St. Claire County.