Let's grab a sandwich!

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Let's grab a sandwich!

The good old sandwich panel is one of the reasons why precast concrete has been able to increase its popularity so fast in so many markets.

The good old sandwich panel is one of the reasons why precast concrete has been able to increase its popularity so fast in so many markets. No other type of exterior wall panel can offer all the same advantages as the sandwich: in addition to great thermal insulation properties, it enables a great variety of different exterior finishes. Anything from plain grey concrete to prestigious natural stone cladding is possible, all prepared at the factory. When the panel arrives at the building site ready to be installed, the work is easy and requires a minimum number of cranes and men and no scaffolding at all. Thermally insulated façades are increasingly a requirement rather than a recommendation in all parts of the world today. This also applies to countries with a hot climate, as it means that expensive air-conditioning is needed to a lesser degree. The efficiency of heating is almost 100 %, whereas the efficiency of cooling is only about 30 %; in other words, cooling consumes three times more energy than heating. Simultaneously with this development, a discussion has arisen on the superiority of the sandwich panel and the double wall. The differences between prefabricated double walls and precast sandwich panels are significant.

Sandwich panels for a perfect end result

Firstly, the thermal insulation properties of the sandwich panel are considerably higher than those of the double-wall. "Attempts have been made to insulate double walls already at the factory, but this has not been any great success", says Mr. Esa Enqvist, Director of Sales and Marketing at Elematic. "Large amounts of material is required both at the factory as well as the site, and against all intentions, it also requires lots of labour. The sandwich panel is both faster and easier to produce, and the end result is notably better." Secondly, with double walls, more work phases are required. The element that is transported to the construction site may have been insulated at the factory, but if not, this must be done at the site. After this, the element is filled with concrete and only then is it ready for use. This entire process means that more workers are required, the site is messy, more scaffolds need to be erected, and even then the result is not satisfactory. Double walls are heavier than sandwich panels, and this affects the foundation of the building, which must be more solid and thus requires the use of even more materials. Third, the sandwich panel enables great variation to the façades of buildings: brick, sandblasting, and numerous other possibilities. With double walls, the finish is limited to grey concrete only.

Elematic's complete sandwich panel technology

Elematic has over 40 years' experience in the production of sandwich panel circulation lines, which just as well can be used for making load-bearing exterior walls. "There are companies that offer you a sandwich panel circulation line that primarily has been designed for filigree slab production. Typically these lines include a side shuttering robot with its own side solutions. Our production line is based on the Elematic Fastening System FaMe, which is easy to use, light-weight, and extremely flexible even when making massive wall elements", describes Mr. Enqvist. "Elematic can deliver sandwich panel manufacturing technology for various requirements, starting from lines with just a few tilting tables for small scale manufacturing all the way to different moving table systems that satisfy even the most massive production requirements." "So why invest in a robot that slows down the performance of the entire line", says Mr. Leo Sandqvist, Managing Director of Elematic. "As slab thicknesses increase along with the insulation, the sides become ever heavier and each edge profile requires its own sides. This is a big investment, even more expensive than the robot itself. The robot does not even disassemble the side equipment; this must be done by hand and requires a manipulator, as the steel sides are extremely heavy." For massive elements, the requirements imposed on the mold surface needs to be taken into account as well; load-bearing capacity must be a minimum of 500 kg/m². There are also many different compaction techniques available on the market. "Experience has shown that as the slab thickness grows, horizontal compaction tables no longer function faultlessly, a deficiency that is emphasized in sandwich panel production. For the best possible end result, traditional vertical vibration techniques must still be used", Mr. Sandqvist concludes. Mr Enqvist will give a presentation at The BIBM Congress 2008, on Thursday, 8th May with more information on sandwich wall production.

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