Stone Inside: Innovations for a Better Climate

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For quite a long time fibre reinforced natural stone has been offered for kitchen tops, elevator covering or noble bathrooms. However, the latest developments of the Munich company TechnoCarbon expand these ranges of application and will grant natural stone new importance as an environmentally-friendly construction material.

The development of the past ten years of the electrical engineer Kolja Kuse, his brother Björn, a stonemason, and the plastics engineer Siegfried Brauner is something we have absolutely no experience with: natural stone as a replacement for aluminium? Natural stone instead of reinforced concrete? Natural stone as an alternative to steel laminated springs in lorries? Natural stone as part of plane wings or helicopter rotors?

Compared to this, extra thin kitchen tops with invisible cooker tops or a heated walls in a bathroom seem to be rather normal. These ideas, which have been introduced at the Materialica, EuroLite or Stone+tec fair, may be daring but they are definitely not crazy. They are just innovative. Carbon fibre reinforced composites have been known for quite a while. Light and robust bicycle frames, nearly complete cars, lamella reinforcements for concrete constructions as well as reinforcement for thin natural stone tiles etc. have been made with this material.

High compressive and tensile strength

What are the advantages of the combination of natural stone and carbon fibre? This is very easy to explain: CFS (carbon fibre stone) has got better properties, as natural stone provides for an enormous pressure resistance and still can be compressed, whereas carbon fibre guarantees a tremendous tensile strength combined with a low traction elongation. If the stone is prestressed and then joined with a high traction by means of epoxy resin it can be loaded and formed by an incredible degree without breaking.

The secret of the patented method is to compress only the stone itself, whereas the tractive force is absorbed by the carbon tissue nearly without stretching. This can be made visible with a granite slab with a thickness of 3 mm but a size of three and a half square meters, which is reinforced on its bottom side. If it is lifted by two people it sags more than 30 cm – but is not damaged at all. If it were turned upside down, it would break immediately, however.

And this is what Kuse’s and his colleagues’ second innovative idea is based on: what about coating both sides of the stone with these fibres and produce a construction material which is light and robust at the same time, and which consumes a lot less energy during its production than steel, aluminium and concrete, and, moreover, offering scores of technological advantages which have not been very well known up to now.

Lightweight and dimensional stable

There are more reasons for the core made of stone, e.g. the specific weight of granite corresponds to the specific weight of aluminium – a fact which is hard to believe - and weighs only about one third of steel. That means, stone is light! However, the pressure load capacity of granite is as high as of constructional steel and four times as high as of normal construction concrete.

What is more, the temperature-related expansion of natural stone (which is low, anyway) is being compensated by the negative temperature-related longitudinal expansion of the carbon fibre. It contracts when the temperature rises but gets wider. That means, CFS can be manufactured in a way that it practically does not change it dimensions under temperature changes, which is a great advantage compared to metal.