As a retired engineer, Alan Sirkin knew that you never, ever mixed naturally corrosive seawater in concrete when building something.
“Absolutely not,” said Sirkin, 75. “Who even thought that could ever be possible?”
Little did Sirkin realize that one day life would lead him to break that sacrosanct engineering rule and build a dock outside his Miami Beach home using concrete mixed with sea water. And no, Sirkin had not gone crazy — he had chosen a path of innovation that University of Miami researchers believe will one day lead to more sustainable construction.
Only 2.5 percent of Earth’s water is freshwater, and mixing concrete demands a significant amount of this scarce resource — one tenth of the world’s industrial freshwater consumption.
That’s because steel rebars are used inside concrete to reinforce structures, and steel corrodes from the chlorides in salty seawater — “the enemy of steel,” said Dr. Antonio Nanni, chair of the University of Miami’s Civil, Architectural and Environmental Engineering Department. But without steel, concrete is brittle and can crack and crumble under stress.
So, instead of steel rebars, the foundation of Sirkin’s dock relies on fiber reinforced polymer — an equally strong if slightly more expensive material that significantly extends the lifespan of structures that use it.
The dock is built with a form of sea-water based concrete that UM researchers have developed in collaboration with the Polytechnic University of Milan, the Florida Department of Transportation and industry partners. UM calls its product Seacrete.
“We have replaced completely steel reinforcement,” Nanni said. “The issue of corrosion has totally disappeared.”
By 2050, the majority of demand for water in concrete production will occur in regions experiencing water scarcity. Concrete is a massive industry, and four billion tons are pumped out every year. Sea-water concrete could help limit water usage and increase longevity of concrete structures.
“Currently, construction industry codes prohibit sea water-based concrete,” Nanni said.
But he is confident that as researchers prove the viability of fiber reinforced polymer as a replacement for steel, the industry will open up to more sustainable and therefore cost-effective alternatives.
“This little project is iconic in the sense that it allows the public to understand what we can do in the construction industry to really become more responsible to the needs of society,” Nanni said.
Nanni predicts that Sirkin’s dock — originally made of wood and destroyed by Hurricane Irma — will last at least 100 years.
Vanessa Benzecry, a University of Miami College of Engineering graduate student who spearheaded the project with Miami-based Dock and Marine Construction, foresees that sea-water concrete could eventually revolutionize the construction industry, especially in coastal areas like South Florida.
“If you’re doing construction from the water, you can take the sea water near you and mix it on site,” Benzecry said. “That would eliminate the transportation cost of freshwater.”
Sea water-based concrete will be especially useful for island nations, like in the Caribbean, with limited access to freshwater, researchers said.
Sea-water concrete is not a new phenomenon — the Romans used a version of it for their coastal buildings, many of which still stand today. These structures actually strengthened over time due to a chemical reaction between sea water and the hydrated lime mortar used in Roman concrete.
“Romans were masters of building marine structures in the sea,” said Dr. Marie Jackson, a geophysicist at the University of Utah. “The material just keeps responding to its environment and grows new mineral cements.”
The Miami Beach dock is not the only example of sea-water concrete’s attempt to steal the spotlight from its freshwater rival. Recently, the Florida Department of Transportation cut the ribbon on the $7.6 million, 180 foot-long Halls River Bridge in Homasassa Springs on the west coast, made using sea-water concrete and fiber reinforced polymer.
Bridges used to be built with a projected fifty-year life span, but the new design is expected to greatly exceed this by at least 25 years, said Steve Nolan, who oversees composite material structure design at the Florida Department of Transportation. An FDOT study found that corrosion is responsible for three quarters of maintenance costs on bridges.
“Even so, the FDOT does not plan on converting to sea-water based concrete because it would too much of an upheaval to the status quo,” said Nolan. “It’s sort of an all or nothing approach. In other locations around the world I see it as a great option, but we are not going to be mandating it in infrastructure anytime in the foreseeable future.”
Until then, sea-water based concrete will continue to try and make it to the big time. Sirkin, for one, is content with the results of a dock he expects will withstand all the ocean can throw at it.
“Time will tell,” Sirkin said, “but they told me it will last a lifetime.”
View the Miami Herald news video ‘Miami Dock Taps Salt Water In New Concrete Mix‘ below.
Source: Miami Herald
