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Modern Composite Materials Keep Centuries-old Buildings Young

30 May 2006

The vaulted roofs and the walls of the basilica in Padua, Italy, and the monastery attached to it, have been reinforced with Twaron and a combination of Twaron and carbon fibres has been used in the library wall.

Both high-performance fibres, Twaron and carbon, are essential for restoring and preserving the thousands of historic buildings in Italy. They have been used now for about ten years because of their combination of exceptional properties - they are strong and light materials, are easy to apply and do not corrode. As well as this, and this is very important in Italy, they help to absorb the forces of earthquakes. It is for these reasons that the Italian government stimulates the use of composites technology in the restoration and preservation of Italy’s cultural heritage. Other buildings that have already been preserved in this way include the Venaria Reale in Turin, the Franciscan monastery in Carrara and the St. Petronio Basilica in Bologna. This application has really taken off, and is now in use in other types of constructions, such as building motorways, bridges and viaducts.

The use of these materials is thanks to Professor Lino Credali, General Director of the firm of Ardea Progetti e Sistemi and former Professor of Polymer Chemistry at University of Padua and Ferrara, as well as Professor of Material Science at University of Modena. Ardea is specialized in the design of constructions from composite materials. The company has its own patented process, Betontex, for the production of unidirectional, thermo-welded, reinforcement materials for constructional applications.

Prof. Credali: ""The most important advantages of Twaron are the excellent mechanical properties, the high tensile strength, the high modulus and the very the very high elongation at break. The material absorbs a large amount of energy when stretching and, what is very important, it also easily absorbs vibrational energy because of its specific crystal structure. These properties make Twaron admirably suited for constructions that have to withstand earthquakes and subsidence.”

Credali uses Twaron particularly for the restoration of brickwork and vaulted roofs, and for masonry walls at the top of buildings. In the past these load-bearing constructions in domes were reinforced with cement beams and stringcourses, but this caused a major increase in weight and with this the chance of damage in the event of an earthquake. Twaron has a comparable modulus to brickwork, but it is much more flexible than the brittle combination of stone and mortar. Twaron aramid gives brickwork the necessary strength and toughness. It also prevents cracks from spreading further.

Twaron

The combination of carbon and aramid fibres in one fabric produces a reinforcement material that combines the best properties of both fibres: carbon absorbs forces generated by the permanent loads, while aramid absorbs the tension forces and the extra forces arising during exceptional circumstances such as an earthquake or subsidence. Prof. Credali: “It can be compared to the use of springs and shock absorbers in a car. Carbon works like the spring and aramid as the shock absorber without adding weight.”

Twaron

According to Prof. Credali applying the fabric is very simple. “First of all, a wall or ceiling is smoothed using cement. When this is dry we apply an undercoat of a layer of epoxy that penetrates the pores thoroughly and ensures that further layers will bind well. After that a layer of thixotropic epoxy resin follows in which we can stick the fabrics. We continue this process layer by layer until we have formed a laminate. The advantage of the material is that we can easily apply it around all the corners and curves that old buildings always have. Finally, we mix sand into the resin while it is still fresh, so that the top layer of plaster will bind well. After that the surface can be painted.”

Prof. Credali estimates that half a million square meters of composite fabric have already been used throughout Italy in civil constructions. Ardea’s sales volume has grown between 20% and 40% per year recently and he expects this to continue for the next few years. “Composite materials provide new design possibilities. Traditional materials were selected on the basis of their intrinsic properties, while composite materials are designed according to the actual application. Their use will continue to grow as more designers learn to work with these materials.”






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