Biorock (also seacrete) is a cement-like engineering material formed when a small

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

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 a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s placed in

seawater Seawater, or sea 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 approximat ...

causing dissolved

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s to accrete onto the

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

to form a thick layer of

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

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

corals Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

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 sufficiency of disclosure, enabling discl ...

s and a

trademark A trademark (also written trade mark or trade-mark) is a form of intellectual property that consists of a word, phrase, symbol, design, or a combination that identifies a Good (economics and accounting), product or Service (economics), service f ...

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 (VC) is a form of private equity financing provided by firms or funds to start-up company, startup, early-stage, and emerging companies, that have been deemed to have high growth potential or that have demonstrated high growth in ...

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 Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

(

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

) combines with

magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

and hydroxyl 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 bioche ...

(HCO3-) to harden the coating to a

hydromagnesite Hydromagnesite is a hydrated magnesium carbonate mineral with the formula . It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine group, serpentine or brucite. It occurs as incrustations a ...

mixture with gaseous oxygen evolving through the porous structure.

Compressive strength In mechanics, compressive strength (or compression strength) is the capacity of a material or Structural system, structure to withstand Structural load, loads tending to reduce size (Compression (physics), compression). It is opposed to ''tensil ...

has been measured from , comparable to the

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

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 is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

into the

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

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

volt The volt (symbol: V) is the unit of electric potential, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

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 Renewable energy (also called green energy) is energy made from renewable resource, renewable natural resources that are replenished on a human lifetime, human timescale. The most widely used renewable energy types are solar energy, wind pow ...

source such as a small floating

solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...

array. One kilowatt hour of electricity accretes about of biorock, depending on parameters such as depth, electric current,

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

and water

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

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