The complex puzzle of 3D concrete printing captured in a model: from layers to bridges
Researcher Rob Wolfs gains his PhD today, for his model which made it possible to print concrete structures in a wide variety of shapes.
The promise of building with 3D concrete printers is great: freedom of shape, personalized designs, faster construction, and more sustainability. It comes as no surprise that in recent years all kinds of initiatives have been launched in this area. But concrete printing is not as easy as it sounds. Freshly printed concrete is still soft, with may cause walls to buckle, sag or fall flat during printing. Curing quickly therefore seems a must. But not too fast, otherwise the printed layers will not bond and cracks will occur. What makes it extra complex is that this interplay of curing, bonding and the increase in forces as the structure grows during the printing process, is different for each printable shape. PhD student Rob Wolfs managed to solve this puzzle. When he started it was difficult to put three layers neatly on top of each other. Now, four years down the road, the concrete printer prints bridges.
A structural engineer normally only needs to calculate whether a structure is satisfactory when it is ready. The special thing about 3D printing is that the construction must also be stable and retain its shape during production, as there is no external support for the unhardened concrete. That too needs to be determined in advance. This was completely new territory that Wolfs explored.
Moreover, the final 3D-printed concrete construction is completely different from conventional concrete, which has been poured into a formwork with reinforcement in it. Printed concrete consists of flat layers, which must adhere well if the material is to behave as a continuous concrete structure. To guarantee shape integrity and, above all, safe structures, the PhD student had to build up the relevant knowledge virtually from the bottom up.
Among other things, Wolfs performed tests with different types of printing mortar, different time intervals between successive layers, and different structures. He saw a lot of concrete walls fall over during printing. But that ultimately led him to understand under what circumstances and with which settings stable concrete structures can be made with concrete printers. Also the model indicates whether a designed shape can be printed at all. In those cases the model gives suggestions how the shape should be altered to become printable.
The work of Wolfs is already embedded in several concrete results. One of them is the cyclist's bridge at Gemert, that was printed and installed two years ago. A second bridge and the first house of 3D-printed concrete will follow soon.
Rob Wolfs continues his research at TU/e, in the group of professor Theo Salet. His dissertation is available online.
Update September 13th: Rob Wolfs has obtained a PhD cum laude for his research.