Carbon-fibre reinforced stone - Technocarbon

52 JEC Composites Magazine / No38 January - February 2008

Applications

Carbon-fibre reinforced stone

USERS’ PLATFORM

ew people know that natural stonehas the same specific weight asaluminium and is as pressure stable

as construction steel - stonecutters haveeven been known to describe stone asbeing relatively flexible under certainconditions. German companyTechnoCarbon Technologies (Munich) hasutilized the above properties to allowcompressing and preloading granite withthe help of carbon fibres, to produceCarbonFibreStone (CFS), a highly durablemethod for stabilizing natural stone.

The carbon-fibre reinforcement protectsthe stone against breakage, thus creatingnew mechanical properties. Highlypressure-stable natural stone, such asgranite, is combined with extremelytension-stable carbon fibre that consists ofnearly 100% pure carbon. The materialscan be bound with highly stable epoxyresins, for example. The carbon-fibre/stonebond is adjusted by hardening the epoxyresins with a specific preload, resulting ina composite material with a combinationof completely new and formerly unknownproperties. This constitutes atechnologically sound way to replace (atleast to some extent) metals, that are CO2

emission intensive.

Technical descriptionTo develop its CarbonFibreStone,TechnoCarbon Technologies used patentedtechnology to encapsulate the stone withcarbon fibres, opening up the possibility tocombine the following material properties: - extreme pressure stability comparableto that of steel,

- extreme tensile strength,- high elasticity combined with unmatcheddynamic damping characteristics,

- high dimensional stability,- minimal coefficient of thermal expansion(1-3),

- much lower specific weight than steel oriron (three times as low),

- a specific weight that, depending on thetype of stone, is the same as or lower thanaluminium,

- unlimited availability.

The new material can be used to produceconstruction elements and bearingstructures that are lightweight, elastic butpressure-stable, torsionally stable, andvibration-damping. They are also resistantto fatigue, chemicals, and corrosion. Inother words, they are in many wayssuperior to traditional materials like steel.Another advantage is that CFS constructionelements can easily be processed andhandled using conventional stone-industrymethods and instruments like drilling,sawing, screwing, or gluing.TechnoCarbon Technologies is interested inworking together with industrial partnersand scientific institutions, and is currently

identifying partners for developing themultiplicity of potential technicalapplications.

Natural stone slabs forkitchens Another aspect of CFS technologyinvolves coating one side of normallytreated natural stone with thin films ofcarbon-fibre matrix in order to stabilizethe stone so thoroughly that it becomes“flexible” and unbreakable. This isachieved by preloading as a function ofthe specific application. These sheets aremore stable, yet about three times lighterthan massive natural-stone coverings 3 or4 cm thick. The carbon-fibre materialstabilizes the worktop up to temperaturesof 120°C and even higher, depending onthe application. The coefficient ofexpansion of carbon fibre is negative,which keeps the stone from breaking over

Fibre-reinforced natural stone has been used for a long time for kitchenworktops, elevator carpeting or elegant bathrooms. TechnoCarbon Technologieshas now developed a composite made of carbon fibre and stone that can be usedin many more applications. The new material gives natural stone a newrelevance as an environment-friendly material.

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Bulthaup kitchen top, 10-mm "Angola Blue"is covered with a CFS layer

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a wide range of temperatures (-40°C to +120°C). The dilatation of the stone canalso be forced to zero if necessary.

Developing a ski with a heartof stoneSwiss company Zai AG worked withTechnoCarbonTechnologies to developthe Spada, the first ski ever made usingnatural stone. The new ski waspresented to the market at Munich’sInternational “ISPO 2007” trade fair forsports equipment and fashion. Thecomposite material used consists ofnatural granitic gneiss from the SwissAlps coated with a carbon-fibrelaminate. Bonding these two ideallycomplementary materials togethercreates new mechanical ¬andengineering properties. The projectturned into an exemplary demonstration

of the flexibility of CFS. Because the natural stone used for theSpada ski has a lower specific weightthan aluminium, and because of CFS’ssuperior vibration-damping properties,the ski has incomparable handlingproperties. This means safer carving athigher speeds, simply because "theflutter" is better absorbed than withother materials. CFS opens up a newdimension in ski design, because itworks with the other materials used tobetter distribute the absorbed vibrations.

Wide-ranging futureapplicationsBy committing to the potential of CFS,manufacturers will soon come up with newideas for applications. CFS beams couldrevolutionize architecture and bridge-building, and it could replace steel

reinforcements or, even better, reinforcedconcrete. Earthquake-resistantarchitecture or lightweight collapse-resistant hall roofs could be designedwithout having to resort to expensivevibration-compensating techniques. Evena top producer of photovoltaic equipmenthas shown interest, seeing the possibilityfor replacing aluminium and steel with amaterial that poses fewer problems.

In car bodies, the material could providesignificant weight savings combined withhigher crashworthiness. In boat-building,it could provide higher torsional stabilitywith greater resistance to breakage. Inmachine construction, where vibrationbehaviour is often hard to control, CFScomponents could offer lightweight buthighly stable and low-vibrationconstructions that are fatigue resistant.Applying CFS to wind-turbine rotorblades or airfoils is another possibility,here again due to the uniquecombination of properties such as highstrength, vibration damping and fatigueresistance with elasticity and low weight.

And finally, CFS technology meetsenvironmental requirements, which areclose to its designer’s heart. It can beused to manufacture raw materials thatcan be machined in an environment-friendly way with the possibility forrecovery, and which consume much lessenergy than the production of steel,aluminium and concrete. �

More information: www.

No38 January - February 2008 / JEC Composites Magazine 53

Fig.2: The Spada stone ski, named for the Rhaeto-Romanic word for "sword"

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