Rapid growth means rapid construction. And if a product can reduce building time and the number of workers on site, builders can save costs. That's where prefabricated concrete slabs come in. Dr Armin Wuensch, managing director of Emirates Filigran, tells Construction Week how demand for hollow core slabs has revolutionised the industry.
Rapid growth means rapid construction. And if a product can reduce building time and the number of workers on site, builders can save costs. That's where prefabricated concrete slabs come in.
Dr Armin Wuensch, managing director of Emirates Filigran, tells Construction Week how demand for hollow core slabs has revolutionised the industry.
Why are you bringing this new floor system into the market now?
Firstly, Filigran slabs are not a new system. It became popular 30 years ago when more and more factories for such products were built in Europe. The parallel development of handling-robots, suitable software and factories producing lattice girders were all important.
Secondly, the UAE construction boom resulted in the erection of a large number of factories producing hollow core slabs, which indicated a huge market for pre-cast floors.
Can you describe what your system actually is?
Filigran slabs are pre-cast slabs with a statically incorporated layer of in situ concrete.
The 5cm - 7cm thick pre-cast concrete element contains the bending resistant reinforcement required for both assembly and the lateral bending tensile reinforcement in the finished construction in the form of lattice girders.
All required recesses, ceiling apertures, electrical sockets, drip noses, slopes and fixtures are taken into account. The prefabricated slab acts as shuttering during the building phase and after the addition of in-situ concrete is effectively a single slab.
How do you manufacture these slabs?
Filigran slabs are produced in CAD/CAM controlled pre-cast concrete plants using the most modern methods to achieve the highest quality standards in regard of concrete, reinforcement and size precision.
The computer gives the planning information to the production plant.
Here the robot sketches the shape and recesses of each slab on a thoroughly cleaned steel mould of 2.5m or 4m width and 12.5m length. The robot cuts and bends the required reinforcement and lays it precisely at the right place.
Consequently the concrete is poured to the final thickness. The pallet with concrete is then vibrated and subsequently transported to the closed curing chamber where the slabs harden under controlled humidity conditions.
How do you handle a 5cm thick concrete slab of several square metres without risk of it cracking?
The basic elements of Filigran slabs are lattice girders, which stiffen the slabs during handling. The system is proven by millions of m2 already produced all over the world.
You mean the lattice girder is a lost item just needed for transport?
Not really. Lattice girders guarantee the bond between slab and concrete during assembly and the two lower bars can be added to the structurally required reinforcement.
Also the height of the girder is chosen so that it can be used as a distance holder for the upper reinforcement.
How high can you build with these slabs?
Height is not an issue at all, as the system can be seen like a monolithic solid floor. There is no restriction in building height caused by this system.
What about system approval?
In Europe the system is well accepted, so the new European norm does not require the manufacturers to apply for a production licence. Still, a number of codes apply. We supply our customers with detailed technology information.
What does it mean for the structural engineer? Must he change his calculation?
If the calculation for a solid concrete floor has already been done, no new calculation is required. We would take over the calculation for the lower reinforcement (cm2/m) and lay exactly the required numbers of bars into our slabs.
Which means you supply the lower reinforcement?
Yes, although this is the reason why we cannot always answer the question which comes first: How much does it cost? Only when we know the reinforcement required can we answer that question.
So, how much does it cost?
Let me give you an example. For floor spans less than 8m we are unbeatable in price. The advantages add up, and anyone who really has effective cost control in his business will talk to us. There are savings in time, and also savings in terms of materials.
How does this system contribute to sustainable development?
Through the material savings. There is no need to purchase expensive plywood or other shuttering items; formwork release agent; spacers; there is no need to move massive formworks in and out from floor to floor; not to mention savings in electrical or plumbing works.
No plaster is required and less paint is needed as slabs are smooth and dense at the surface.
In short: Filigran slabs reduce the number of work stages required for construction purposes by about 50% when compared to on-site moulded slabs.
As well as the sustainability contribution, this also means a large saving in cost.
Are you a competitor to hollow core slab producers?
Yes and no. For spans over 9m the pre-stressed slab is more feasible in many applications.
For shorter spans, Filigran slabs offer a number of features, which hollow core slabs cannot compete with.
The undersides of Filigran slabs are smooth, plain, straight and ready for the painter; no plaster is needed; the architect has nearly unrestricted ground plan possibilities; holes and cut outs can be accurately formed during manufacture; electrical or plumbing parts can be fixed before the final site concrete is placed; a concreted floor with Filigran slabs is a monolithic unit with all structural advantages; Filigran slabs are usually just 5cm thick and therefore light; handling is safe and easy, meaning large areas of floor can be erected in a short space of time; and extremely low size tolerance.
What are the advantages of Filigran slabs compared to solid concrete floors?
Time and money. Both points are vital for any contractor. He saves time because only about 50% of the work stages have to be done, for example, there is no laying of lower reinforcement and no plaster required.
All these points are also connected to the cost aspect. Alone savings in plywood are huge. The contractor needs no spacers anymore and no formwork release agent, just to name a few items.
Above all, the product reduces construction time enormously and it also reduces the number of workers at the site.
What type of buildings is your sales staff targeting?
One very interesting advantage of our system is its versatility. A contractor, who has to build just two floors of a villa with, say 200 m2, can come to us and will get his slabs within days.
A large contractor having 200 villas with 40,000m2 will be equally served as our production exceeds 1000m2 per day. Office buildings, hotels, parking decks or labour accommodation buildings with reasonable spans are also in our view.
How about floors for pre-engineered buildings?
Filigran slabs are absolutely ideal for this type of construction. First because of the monolithic slab effect. Second, we can make all recesses around columns in the factory at precisely the place where they must be. And third, the slabs are light and easy to handle by crane. Shear studs welded onto the beams achieve necessary composite bond.
What are your next plans?
We are currently building a second plant for the production of "double walls." In principle we put two Filigran slabs standing vertically together, leaving a small space in between which is later filled with cast-in-situ concrete.
This double wall system eliminates all the complicated and expensive connections which you have with standard pre-cast elements.
In addition to this advantage both wall sides are very smooth and ready for paint. Of course, we can also add insulation if required.