ANN ARBOR, MICH. - There are two KitchenAid mixers sitting on the counter and next to them, a mixer that looks like it’s been taking designer steroids for a decade.
Into that giant mixer go a bunch of dry ingredients. The mixer whirs to life and stirs for five minutes or so.
Then, the liquids go in and the mixer whirs back to life and shortly, the recipe is done.
But this isn’t your grandma’s kitchen – and the finished product isn’t holiday cake batter. It’s a lab in the basement of a University of Michigan building and the stuff inside the mixer bowl is concrete – ultra high-performance concrete to be exact.
And while it’s existed before, a team of U-M engineers has come up with a non-proprietary formula that has all sorts of potential uses.
It could be used to create better roads that don’t turn into a pothole maze as fast; help build super-strong, super-tall buildings and even have uses in making blast-proof buildings.
“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, a U-M professor of civil and environmental engineering. “However, UHPC can support at least 22,000 psi or six times as much.”
In addition, the concrete is built to better handle freeze/thaw cycles, which contributes to the creation of those pesky potholes. Regular concrete is good for about 28 cycles. This concrete is good for 90 cycles or more.
So, how does it work?
The super-strong concrete packs more particles into each bit of concrete.
Pretend that the regular concrete is three tennis balls stacked on each other in a triangle. There’s gaps in the stack. This concrete fills those gaps in, and then fills in the gaps in the next layer and so on until there aren’t any gaps. That keeps water from getting in, freezing and then causing problems when it thaws. There’s also thin steel wires mixed into the concrete to help hold it together when it does crack.
The super-strong concrete was developed by a private company, but it’s costly – around $2,700 or $2,800 per cubic yard. Regular concrete runs about $100 or so per cubic yard.
The Michigan Department of Transportation gave U-M a grant to see if it could develop a less costly version.
In 2016, MDOT outlined the problem with commercially available brands of UHPC in a research publication.
“While the durability properties of UHPC are very attractive… mixes are currently prohibitively expensive for widespread use and require specialized equipment and curing practices…,” MDOT’s research report stated. “But if costs were reduced…(it) could have potential…including thin overlays for decks that now need to be replaced every few decades.”
U-M’s version costs about $880 per cubic yard. That’s still much more than regular concrete at $100 per cubic yard.
The reason U-M's is still more costly is largely due to those thin steel wires. MDOT mandates only American-made products be used and the steel wires are more expensive than similar products made overseas.
“Our (concrete) brings down the cost of long-term maintenance,” El-Tawil said. “It’s still more expensive than regular concrete, but if you consider the effect over the lifetime of a bridge, then the cost becomes very competitive.
“If you have a concrete deck on a bridge that lives for 200 years with little to no maintenance … imagine the cost savings.
"I think we should use it for all infrastructure."
U-M is currently working on the best ways to mass manufacture large quantities of the mix. It was used recently in a bridge repair in St. Clair County which MDOT is using as test.
Unlike the private companies already doing the super-strong concrete, U-M plans to give away its formula for the concrete as a way to help it become used more, which the U-M engineers believe will also help drive down the cost.
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