As environmental threats deplete the world’s reefs, precast concrete offers cost-effective and workable methods for restoring them.
By Deborah Huso
While it’s not unusual for precast concrete to be a component of “green” commercial building projects, often helping architects and builders earn points for LEED certification, precast has also been lending a hand on the environmental front through natural habitat-restoration projects. In recent years, environmentalists around the world have been incorporating precast concrete into the construction of artificial reefs, restoring habitats for marine life and protecting fragile coastlines from storm devastation.
Why restore “living shorelines”
The Nature Conservancy is involved in several such projects, including a number of oyster reef restorations in the Gulf of Mexico. According to Amy Smith Kyle, project manager for the Louisiana Field Office Coastal Conservation, scientists at the Nature Conservancy have found that 85% of the world’s oyster reefs have been lost. “These reefs provide a lot of ecosystem services,” she says. “They make for fantastic fish habitats, and they’re natural coastal buffers that help break up wave energy.” Oysters are also filter feeders, meaning their presence in the ecosystem improves water quality. “They’re essentially living shorelines,” Kyle adds.
The importance of oyster reefs to the ecosystem, where they provide habitat for juvenile fish, shrimp and crab – and protect human populations on the coast during hurricanes and other severe weather events – has led The Nature Conservancy to initiate a number of reef restoration projects along the northern Gulf of Mexico. The conservation group is placing artificial reefs where oyster reefs have historically been located.
Testing precast in Vermillion Bay
In Vermillion Bay off the coast of Louisiana, the Conservancy is testing precast concrete in its restoration of oyster reefs along the National Audubon Society’s Paul J. Rainey Sanctuary. The Conservancy is using a patented Oyster Break system developed by Wayfarer Environmental Technologies based in Hunt Valley, Md. Wayfarer’s Mike Turley explains that the system basically looks like Olympic rings sitting in the water. The system of rings is designed to perform several functions, including protection of the coastal shoreline from erosion.
The precast concrete rings measure 5 ft in diameter. The first phase of the project was completed in October 2010 with the placement of 670 linear ft of rings. The second phase began in the summer of 2011 with the installation of another 685 ft, and the third phase will add 1,700 more ft. “A big part of the this project is trying to see what types of oyster reef restoration projects work best in which habitats,” Kyle explains.
To attract oysters to the precast rings, Wayfarer adds a proprietary organic mix to the concrete. “We have a high attraction rate,” Turley says. “Oysters tend to attach themselves at the ends of the shelves, so you actually end up with higher-density reefs. The bigger the structure gets, the bigger its capacity to deal with storm surge.”
Wayfarer is the provider of the molds for the precast rings, and with each project, the company brings the molds to the local area and uses local precast concrete manufacturers to cast the rings, which weigh in at one ton apiece. To install the rings, contractors use an airboat with a crane boom or standard barges with excavators that position the rings in the water. The ring design in Vermillion Bay consists of six segments of 225 linear ft, each with a 100 ft break in between each segment.
Why precast works
The reef production process is fairly quick. Turley says precast manufacturers pour concrete into Wayfarer’s forms, which can then be broken in two to three hours. “That avails itself to just-in-time delivery,” he points out, “and also reduces standing inventory requirements.” The rings are generally ready to ship within 10 to 14 days. Turley says he can get any reef project going in as little as 30 days.
Turley feels precast concrete offers some distinct advantages. “You get much better consistency and strength from precast, and it also minimizes transportation costs,” he says.
Precast also offers flexibility in mix components. “We can use different size stone and admixtures, allowing us to custom design for particular habitats and customers,” Turley notes. His company is able to fine-tune the concrete mix profiles based on local aggregates.
Turley says precast also offers weight capacity that keeps the rings in place. They are not easily shifted by waves or storm surges. At the same time, the rings offer a lot of flexibility in design.
While it’s still too early to make any definitive assessments on the effectiveness of the precast concrete oyster reefs in the Gulf, Kyle says oysters are attaching in Vermillion Bay. “They seem to really like the texture of the product,” she says.
Reef balls offer solutions worldwide
Precast concrete rings aren’t the only method of artificial reef restoration being used. The Reef Ball Foundation, based in Athens, Ga., has helped place precast concrete reef balls in more than 4,000 reef restoration projects in some 60 countries. Their projects include not only oyster reef restoration but coral propagation and planting systems, estuary restoration, mangrove restoration, and beach erosion control projects.
Like Wayfarer, the Reef Ball Foundation, in partnership with Reef Innovations Inc. in St. Cloud, Fla., has a variety of molds that are shipped to the reef restoration site. A local precaster then fills them with concrete, micro silica and aggregate, which cures for 24 hours. The foundation also sends its clients additives like the micro silica, which increases the reef balls’ durability and strength and establishes resistance to corrosion. Adva Flow is also added to the mix to keep the reef ball pH low so it’s close to that of seawater. Microfibers added to the concrete create a rough texture to encourage organisms to attach. With most of the weight at the bottom of the balls, they are also less likely to shift during severe weather events.
Kirbo says the balls are especially useful in coral reef restoration because they mimic the limestone boulders to which organisms attach.
Currently, the Conservancy has placed a total of 3,500 reef balls in and around Mobile Bay. “The Reef Ball Foundation and Reef Innovations have been around quite awhile and have had success with oyster attachment,” DeQuattro says. He says the reef balls provide particularly good habitat for fish, since they are hollow and filled with holes.
“In the old days of artificial reef creation, people put down trash, tires, ships and cars,” Kirbo explains, “but those things all shift under water and have toxins, too,” adding that precast concrete offers a much more environmentally friendly and stable option for reef restoration.
Deborah Huso is a freelance writer who covers home design and restoration, sustainable building and design, and home construction.