Can concrete bend? No, of course not!! … or can it ?!?!
Several years ago, during the installation of a specially designed staircase, I received a call from the building site: The front end of two of the element plates did not align properly, and could not be aligned by simple adjustment of the elements due to other restraints. And it did not look nice.
To solve it, we used the fact that concrete creeps when loaded, and, that these particular elements were quite young at the time. So a 1½ ton weight was placed on one element, and a support placed under the other, and then we waited for 4 days, and removed the weight. And voila, the element plates were aligned – and stayed aligned.
This radical quick fix was only possible because in CRC i2®, cracks do not form in a normal way, because of the special strain hardening properties of the material, and the exceptionally short time it takes to reach a long term quasi steady state for CRC i2®.
This principle has been used, both before and after, to solve similar alignment problems, straighten elements stored with less than optimal support, etc. It is also why correct storage is so important.
Years later we were discussing bridges, and the necessity to make curved elements to match the curvature of smaller bridges with Hi-Cons cooperation partner Pieters Bouwtekniek (NL) and the idea to perform this bending with CRC i2® as more than a problem solving measure was conceived.
Now, several years and a lot of testing later, both initially at TU Delft (NL) and later with full scale documentation trials at Hi-Cons plant in Hjallerup (DK), we have the data necessary to actually execute controlled cold bending of pre-cast CRC i2® elements.
Yes we bend concrete. Deliberately.
And why is this useful you might ask, and not just a crazy idea – well, because a large part of the cost of production of concrete elements is the formwork cost, and especially formwork to produce curved elements (having both a bottom and top side) is expensive – as is the required work hours to reinforce and cast curved elements conventionally.
Using the cold bending technique, we can produce CRC i2® elements without an excessive extra formwork cost, just adding a specialised and well-defined storage period to the production cycle.
The unique technique can for instance be used to create a precamber without casting the curvature, or using pre- or post tensioning, making increased spans for a certain plate thickness or reduced thicknesses for a fixed span possible – or something completely different, like the bridge elements we discussed in Holland.
Therefore, I would like to invite You to contact Hi-Con with ideas or projects for trying out this novel technique – we love a good challenge!
Tommy Bæk Hansen
Group Product Development Manager
Read about Tommy’s 20 years of experience with UHPC right here