A new water-repellent 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 analysing 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 minimise the need for repair."
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.