The startup’s paper-based stainless steel could change how bridges are built

The scourge of modern concrete is, perhaps surprisingly, rust.

Most concrete structures are placed with steel rebar to add strength, but if the metal corrodes, it can cause the concrete to fail prematurely. Bridges, which are exposed to water and salt, are some of the most vulnerable. Nearly one-third of bridges in the United States need to be Repaired or replacedwhich could cost approximately $400 billion over the next decade.

There are lots of ways engineers deal with rust, from coating rebar with epoxy to pouring extra concrete to buy some time before water gets to the rebar. Ultimately these measures also fail. The only way to really prevent problematic rust is to use stainless steel rebar, which is not cheap.

“It’s too expensive to use on every bridge,” said Stephen Gebele, co-founder and CEO of Allium Engineeringhe told TechCrunch. So cities and countries will only switch to the most important ones.

But Allium suggests a compromise, of sorts, by covering the regular rebar with a thin layer of stainless steel to extend the bridge’s intended life from 30 to 100 years.

“As long as we get complete surface coverage, a thin layer is enough stainless steel to where it will resist corrosion for hundreds or thousands of years,” said Samuel McAlpin, co-founder and CTO of Allium.

The startup’s stainless steel rebar was recently used to replace a bridge deck on U.S. Highway 101 in Mendocino County, California, and another is planned for Route 91 in Massachusetts. He also contributed a commercial boat yard in Key West, Florida, Alyum exclusively for TechCrunch.

For critical bridges that carry a lot of traffic, engineers sometimes specify stainless steel, which costs about five times more than regular rebar. Governments consider the extra costs worth it if they don’t have to close a major artery.

But for most other bridges, they tend to specify epoxy-covered rebar, which is just about 25% to 50% More than uncoated rebar. Epoxy-coated rebar should be in covered storage, and any spots or welded spots in the coating should be patched, both of which add additional indirect costs.

Allium brands rust-coated rebar as an alternative to epoxy-coated. The company aims to match and perhaps undercut the price of epoxy coatings in the future. When installed, Allium iron should cost less because it doesn’t have to be handled with care, Jepeal said. Startup’s rebar will also not need the extra concrete that is sometimes added to bridges to rust.

“This extra layer of concrete is not structural. It’s just to try to insulate the rebar and delay how long it takes for the salt to get to the rebar,” Gebel said. Getting rid of this can cut cement usage by up to 20%. Because rebar is not susceptible to corrosion, transportation departments should be allowed to limit the use of green cement, which tends to be less alkaline than standard mixes.

The Allium process wears 7,000 lbs of steel with a stainless steel coating, and essentially welds the wires to the outside until they are fully coated. These pallets, which range from six to eight inches square and 40 feet long, are then fed through a series of rollers until they reach the desired thickness, which ranges from a third of an inch to a few inches in diameter.

“By cladding a smaller surface area with a thicker layer and integrating into the milling process, we can do something that is much cheaper, much more scalable, and much easier to control quality,” Gebel said.

Because the billet is tempered, up to 150 times longer in the process, stainless steel also works. Finally, each piece of rebar is finished with approximately 0.2mm of stainless cladding.

Even with that small amount, “it’s not going to corrode through that stainless steel in the concrete, basically,” McAlpine said.