08 januari 2016

Ultrathin staircase: a challenging UHPC application

It sounds like the ultimate challenge: design an ultrathin staircase made of concrete. The ingredients are simple. Take the best performing Ultra High Performance Concrete (UHPC) and combine this with substantial reinforcement. The result: a piece of innovative technology with an unprecedented thinness. Mathematically, this far exceeds the boundaries of what, until now, was considered customary. A revolutionary design.

All that remains to be done is the actual implementation. In the standard construction process, the drawings are transferred to the contractor. And then the old adage ‘No news is good news’ applies. Throwing it out of the proverbial window, however, does not apply here. Think about it: how would sticky, reinforced concrete pour in a space with a width of approximately 5 cm? Normal aggregate would already be left in the form. The space is so small that the concrete would stick to the form. All the more reason to integrate the construction process in the design.

To make the staircase ultrathin, the best performing UHPC material at hand is used. This UHPC material is packed with fine steel fibres. The material cannot be compared with many high performance mortars regularly available on the market. The fibres negatively affect the flow of the mortar.

The first steps can easily be taken. Make the concrete self-compacting and do not use large pieces of aggregate. Discuss the reinforcement with the supplier and apply it in a way that minimum blockages occur. The result? The concrete visibly flows into the concrete mould. But is it a good result? And how do we find out?

The solution is simple for the time being: invest money in a formwork and put it to the test. We put it to the test and this is the result: 

Afbeelding: Michael_Menting_UHSB
Design stairs by JHK Architecten

The first result discouraged us and we returned disillusioned to our drawing table. However, we are motivated enough to continue searching for the right solution. Nothing ventured, nothing gained. I will keep you informed of developments at ABT.


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