Biorock (also seacrete) is a

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

-like engineering material formed when a small electric current is passed between underwater metal

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

s placed in

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appr ...

causing dissolved

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

s to accrete onto the

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...

to form a thick layer of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

. This 'accretion process' can be used to create building materials or to create artificial 'electrified reefs' for the benefit of

corals Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secr ...

and other sea-life. Discovered by Wolf Hilbertz in 1976, biorock was protected by

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

s and a

trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from othe ...

which have now expired.

History

During the 1970s Professor Wolf Hilbertz, an architect by training, was studying seashells and reefs at the School of Architecture at the University of Texas. He was thinking about how humans could emulate the way coral grow. After preliminary work in 1975, in 1976 he discovered that by passing electric currents through salt water, over time a thick layer of various materials including

deposited on the

. Later experiments showed that the coating could thicken at the rate of 5 cm per year for as long as current flows. Hilbertz’s original plan was to use this technology to grow low-cost structures in the ocean. He detailed his basic theory in a technical journal in 1979, believing that the process should not be patented so that it could be commercially exploited by anyone. However, having been let down a number of times he incorporated a company, The Marine Resources Company, raised

venture capital Venture capital (often abbreviated as VC) is a form of private equity financing that is provided by venture capital firms or funds to start-up company, startups, early-stage, and emerging companies that have been deemed to have high growth poten ...

and filed a number of

s relating to biorock. He dissolved Marine Resources Company in 1982 as his focus shifted to creating artificial coral reefs (or electrified reefs) after meeting Thomas J. Goreau. Hilbertz formed a partnership with Goreau, who continued work coral reef restoration and biorock after Hilbertz' death in 2007.

Process

The chemical process that takes place on the cathode is as follows: Calcium carbonate (

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

) combines with

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...

and

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...

ions to slowly accrete around the

coating it with a thick layer of material similar in composition to magnesium oxychloride cement. Over time cathodic protection replaces the negative chloride ion (Cl-) with dissolved

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochem ...

(HCO3-) to harden the coating to a

hydromagnesite Hydromagnesite is a hydrated magnesium carbonate mineral with the formula Mg5(CO3)4(OH)2·4H2O. It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine or brucite. It occurs as incrustations ...

mixture with gaseous oxygen evolving through the porous structure. Compressive strength has been measured from , comparable to the

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

used for sidewalks. The material grows rapidly, strengthens with age and is self-repairing whilst power is applied. The process is one that emits

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

into the atmosphere rather than sequestering it. The electrical current, supplied by a low DC

volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...

age (often <4 volts) at a low current, is required on a continuous, pulsed or intermittent basis which can therefore be generated nearby from a low-cost integrated renewable energy source such as a small floating solar panel array. One kilowatt hour of electricity accretes about of biorock, depending on parameters such as depth, electric current, salinity and water

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

. no. 243

Electrified reef

Electrified reefs can be constructed using the Biorock process which provides a substrate on which corals thrive, being very similar to that of a natural reef. The structural element of the reef can be constructed out of low-cost rebar metal on which the rock will form which can be created locally in a shape appropriate to the location and purpose. Power is supplied between this large metal structure (the

) and a much smaller anode. Coral also benefits from the electrified and oxygenated reef environment that forms around the cathode. High levels of dissolved oxygen makes it highly attractive to marine organisms, particularly fin fish.

Patents

* 1981 ( expired) * 1984 (expired) * 1984 (expired) * 1996 (expired)

Trademark

The term Biorock was protected by a

between 2000 and 2010, but can now be used without restriction.

References

{{reflist

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 und 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

External links

Wolf Hilbertz website

Global Coral Reef Alliance
Building materials Concrete Marine biology