Transportation defined: Hydrodemolition and MMC

Transportation defined: Hydrodemolition and MMC

June 4, 2014

We have a couple of new terms for you today and they both have to do with concrete...

First up is hydrodemolition. Simply put, it’s a method that uses a high-pressure stream of water to remove concrete, or other types of surfaces.

David Sikes, a resident engineer in ADOT’s Flagstaff District, explains in the video above that using the hydrodemolition tool is much more efficient than other methods for removing concrete.

“We get this machine that’s got about an 8-foot-wide head with nozzles on it that puts out the high-pressure water and we can take off the surface concrete fairly quickly,” Sikes says in the video. “If we had to do it with chipping hammers, it would probably double the work time.”

Besides being efficient, Hydrodemolition can allow crews to control the depth of the cut they’re making (the machine’s pressure can be adjusted and its nozzles can be controlled). Hydrodemolition also helps control any dust – crews use a vacuum hose to suction water and debris as they go along.

The next term we’d like to define is Microsilica Modified Concrete (MMC).

MMC is a type of concrete that’s mixed with microsilica, which according to the FHWA, “is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys.” MMC has plastic fibers in the mix, too, as shown in the video above.

The result is a dense and durable concrete that is very appropriate for bridge decks like I-15 Virgin River Bridges 3 and 7, Sikes says.

“Trucks traveling south on I-15 carry salt-laden slush from roadways to the north. As the air temperature warms, the salt mixture drops off of the trucks onto the bridge decks.  If the salt is able to penetrate the concrete down to the rebar, the rebar will corrode, causing the concrete surface to pop off,” he said. “MMC is a very dense concrete that will resist the penetration of the salt mixture. We should have a durable bridge deck for a number of years.”

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!