Water Repellent Concrete That Lasts a Century
Water Repellent Concrete could put an end to potholes and cracking highway surfaces
by Michael Keller
A new water repellant concrete impregnated with tiny superstrong fibres promises to leave roads and bridges free of major cracks for up to 120 years.
University of Wisconsin-Milwaukee civil engineers have developed a concrete mix that is durable and superhydrophobic. They call it Superhydrophobic Engineered Cementitious Composite (SECC). Preventing normally porous concrete from absorbing water means that liquid can’t get inside, freeze, and cause it to crack. The concrete’s unusual characteristics, including being significantly more ductile than traditional concrete, means that cracks that do form do not propagate and cause failure.
“Our architecture allows the material to withstand four times the compression with 200 times the ductility of traditional concrete,” said associate professor Konstantin Sobolev, whose lab created SECC.
A report available on the Government Finance Officers Association lists the useful life of typical concrete roadways as 30 years and concrete bridges and culverts as 40-45 years. The UWM team says their improved material will hold up with little or no maintenance for well over a century.
To impart the characteristics in the material they wanted to see, they doped their mix with superhydrophobic additives based on siloxane, a compound that forms the backbone of silicones, mixed with superfine powders. Together, these form a microscopic spiky surface nearly impermeable to water. They also added unwoven polyvinyl alcohol fibres, each the width of a human hair, which are strong enough to let the concrete bend without breaking.
“The use of polyvinyl alcohol fibres in engineered cementitious composite proves to be a very effective method to not only improve the ductility of concrete, but to drastically improve its durability,” the researchers wrote in a June 2013 report on SECC. “Conventional reinforced concrete is a relatively brittle material which, when loaded, typically causes large cracks. These large cracks allow water to penetrate through the concrete, reaching the reinforcing steel and, in turn, cause the steel to corrode, ultimately leading the failure of the reinforced concrete.”
Last August, the team laid a 4-by-15-foot slab of their improved material as a patch to a university parking structure. They embedded sensors in their concrete to monitor moisture, stress and load. They are still analyzing whether the SECC they installed in the structure shows the performance improvement they saw in the lab.
They say the material, which would cost more than typical concrete, would pay for itself with diminished maintenance costs if it performs as they expect. It would also help with the sorry state of civil infrastructure across the country.
“America’s infrastructure is in urgent need of restoration/repair, especially in parts of the country exposed to freezing,” they wrote in 2013. “Freezing and thawing cycles in northern regions lead to loss of performance, demanding urgent repairs and attention or bridge failures… An engineered high-performance and durable material is required for these elements of infrastructure in order to increase the service life of roadways and to minimize the need for repair.”
“Most accidents happen in fall or end of spring, when there’s freezing in the roads,” Konstantin Sobolev explains. “Here in Wisconsin, just a few days ago it was a rainy day and suddenly it was cold and we had ice on the roads. Many accidents happened that way. [SECC] could save lives.”
So far, Sobolev’s lab has tested the material on the university’s own parking ramp. They’ve also inserted carbon nanotubes and 100 electrodes into the material to communicate to scientists how much moisture the ramp will be able to absorb, and how much stress it will be able to take. The researchers’ ultimate goal is that SECC is used commercially to prop up (and communicate with) bridges.
But while SECC holds a lot of promise for pothole applications, too much of it could be dangerous. Impervious, concrete surfaces are contributing to a crisis of stormwater runoff from cities, the kind that can flood sewage systems in a bad rain and push all kinds of pollution out to waterways. Sobolev acknowledges this, but notes that on some surfaces, like bridges, runoff will happen no matter what. Plus, not all applications of the stuff have to be “superhydrophobic.” If you leave off the water-repellent coating, this type of concrete remains remarkably durable, he says.
This post originally appeared on Txchnologist. Txchnologist is a digital magazine presented by GE that explores the wider world of science, technology and innovation. Michael Keller is Managing Editor of Txchnologist. His science, technology, and international reporting work has appeared online and in newspapers, magazines and books, including the graphic novel Charles Darwin’s On the Origin of Species.