Biorock, also called seacrete, is a material similar to cement that forms when a small electric current is passed between underwater metal electrodes placed in seawater. This process causes minerals in the seawater to build up on the cathode, creating a thick layer of limestone. This "accretion process" can be used to make building materials or to build artificial reefs with electricity, which helps corals and other sea life. Biorock was discovered by Wolf Hilbertz in 1976. Patents and a trademark for biorock are no longer in effect.

History

During the 1970s, Professor Wolf Hilbertz, who was trained as an architect, studied seashells and reefs at the School of Architecture at the University of Texas. He was thinking about how humans could copy the way coral grow. After early research in 1975, in 1976 he discovered that by passing electric currents through salt water, over time a thick layer of materials, including limestone, formed on the cathode. Later experiments showed that the coating could grow at a rate of 5 cm per year as long as the current flowed.

Hilbertz's original plan was to use this technology to build low-cost structures in the ocean. He explained his basic idea in a technical journal in 1979, believing the process should not be patented so that others could use it for business purposes. However, after facing repeated disappointments, he created a company called The Marine Resources Company, raised money from investors, and filed several patents related to biorock.

He ended the company in 1982 when his focus changed to creating artificial coral reefs (also called electrified reefs) after meeting Thomas J. Goreau. Hilbertz partnered with Goreau, who continued working on coral reef restoration and biorock after Hilbertz's death in 2007.

Process

The chemical process on the cathode works like this: Calcium carbonate (aragonite) joins with magnesium, chloride, and hydroxyl ions to slowly build up around the cathode, covering it with a thick layer of material similar to magnesium oxychloride cement. Over time, cathodic protection replaces the negative chloride ion (Cl-) with dissolved bicarbonate (HCO3-), hardening the coating into a mixture of hydromagnesite and aragonite. Gaseous oxygen is released through the material’s pores. The material’s compressive strength ranges from 3,720 to 5,350 psi (25.6 to 36.9 MPa), which is similar to the strength of concrete used for sidewalks. The material forms quickly, becomes stronger as it ages, and can repair itself while power is applied. This process releases carbon dioxide into the air instead of trapping it.

A continuous, pulsed, or intermittent electrical current, supplied by a low DC voltage (often less than 4 volts), is needed. This current can be generated nearby using a low-cost renewable energy source, such as a small floating solar panel array. One kilowatt hour of electricity can produce about 0.4 to 1.5 kilograms (0.9 to 3.3 pounds) of biorock, depending on factors like depth, electric current, salinity, and water temperature.

Electrified reef

Electrified reefs can be built using the Biorock process, which creates a surface where corals grow well, similar to natural reefs. The main part of the reef is made from low-cost rebar metal, which can be shaped locally to fit the area and purpose. Electricity is provided between this large metal structure (called the cathode) and a smaller metal piece (called the anode). Corals benefit from the electric and oxygen-rich environment around the cathode. High oxygen levels in the water attract many marine animals, especially fish with fins.

Patents

• US 4246075 "Adding minerals to large surfaces and building parts" 1981 (expired)
• US 4440605 "Fixing damaged concrete structures by adding minerals" 1984 (expired)
• US 4461684 "Coating materials with minerals to prevent breakdown by living things" 1984 (expired)
• US 5543034 "Method to help aquatic life grow and structures made using this method" 1996 (expired)

Trademark

The term Biorock was a registered trademark from 2000 to 2010. However, it can now be used freely without any restrictions.

Published works

• Hilbertz, W. H., Marine architecture: an alternative, in: Arch. Sci. Rev., 1976
• Hilbertz, W. H., Mineral accretion technology: applications for architecture and aquaculture with D. Fletcher and C. Krausse, Industrial Forum, 1977
• Hilbertz, W. H., Building Environments That Grow, in: The Futurist (June 1977): 148–49
• Hilbertz, W. H. et al., Electrodeposition of Minerals in Sea Water: Experiments and Applications, in: IEEE Journal on Oceanic Engineering, Vol. OE-4, No. 3, pp. 94–113, 1979
• Ortega, Alvaro, Basic Technology: Mineral Accretion for Shelter. Seawater as a Source for Building, MIMAR 32: Architecture in Development, No. 32, pp. 60–63, 1989
• Hilbertz, W. H., Solar-generated construction material from sea water to mitigate global warming, in: Building Research & Information, Volume 19, Issue 4 July 1991, pages 242–255
• Hilbertz, W. H., Solar-generated building material from seawater as a sink for carbon, Ambio 1992
• Balbosa, Enrique Amat, Revista Arquitectura y Urbanismo, Vol. 15, no. 243, 1994
• Goreau, T. J. + Hilbertz, W. H. + Evans, S. + Goreau, P. + Gutzeit, F. + Despaigne, C. + Henderson, C. + Mekie, C. + Obrist, R. + Kubitza, H., Saya de Malha Expedition, March 2002, 101 p., Sun&Sea e.V. Hamburg, Germany, August 2002