A brave new world of building

The printed build

Structures straight from the printer? While it may appear rather strange at first glance, 3D printing is one of the major technology-related topics of tomorrow in the construction industry. Experts, planners and contractors worldwide are looking for new concepts to help create a building process that is as quick, cost-effective and environmentally friendly as possible. This applies as much to the sprawling metropolises of industrialised nations as it does to the burgeoning megacities of developing and emerging countries. In the USA, UK, China and not least in Germany, there are a significant number of research and development projects aimed at creating a 3D concrete printing process suitable for mass production. For example, "Beton3D-Druck” [Concrete 3D Printing] is exploring the fundamentals for the introduction of a new construction process as part of the “ZukunftBau” [Future of Building] funding programme run by the Federal Institute for Research on Building, Urban Affairs and Spatial Development. MC’s specialists are providing concrete technology know-how and support to these research projects, as well as highlighting innovative developments in products including concrete admixtures including hardening accelerators and even fibre-reinforced mortar.

Three different approaches currently dominate discussions relating to the 3D concrete printing of structures and components: powder bed technology, the currently more widespread extrusion technique and the wet-spray process.

Powder bed

The powder bed technique is being advanced in two different directions: Either a mixture of aggregates is bonded to a composite by local application of cement paste or consolidation is achieved by selective application of water to a mixture of aggregates and cement. With both techniques, even intricate structures can be produced without any problems. However, with larger components especially, a considerable number of layering cycles is necessary, making the process relatively slow.

Extrusion

In extrusion technology, a die head lays material strands of different shapes, heights and widths on top of each other in layers. It is likewise referred to as an additive technique. This process comes closest to established conventional 3D printing with plastics. Although the procedure is faster, it also has a weak point – in the truest sense of the word. Since the material strands are individually deposited on top of one another, bonding is only achieved by pressing each new strand against the one below it. This can therefore lead to problems in terms of flexural or shear strength and the amount of mechanical stress the construct can bear.

Wet spraying

The wet-spray process is also an additive process and is similar to the extrusion technique. Here, too, the premixed wet-spray material is pumped to a spray nozzle, accelerated by compressed air and applied layer by layer to the substrate. Offering high deposition rates and process speeds, this technique is very well suited for the production of large-format components. In contrast to the extrusion process, the application angle of the concrete spray nozzle can be varied vertically and horizontally. This leads to new possibilities with regard to the geometric shapes that can be generated. However, the ability of this technique to produce intricate structures is very limited. Moreover, the biggest advantage of the process also poses a challenge: While the high pressures brought to bear during application ensure an extraordinarily high level of material compaction, they also give rise to more residues in the form of dust and aerosol pollutants requiring effective control.

So all three techniques have their strengths and weaknesses. Reason enough for two German research projects to focus more intensively on process optimisation in 3D concrete printing.

Research at TU Braunschweig

Under the guidance of ITE, the Institute for Structural Design at TU Braunschweig, an interdisciplinary research group involving TU Braunschweig, TU Clausthal and LU Hannover has been developing a robot-controlled shotcrete technology for the formwork-free production of complex concrete components. From the beginning of the research it was found that the current techniques used in the production of precast concrete parts have not evolved beyond those established on the market for decades. This is in contrast to many other areas of manufacture, where digitally supported production is already well advanced. A lot of potential has thus fallen by the wayside – not just in respect of creative and constructive possibilities, but especially in terms of economic and commercial progress.

This new manufacturing technology enables architects to implement completely original designs for geometrically complex concrete components, providing a level of creative scope that is not available with the techniques currently in use. Beyond freedom in creative design, however, the advantages extend to more efficient material utilisation and the resulting implications for the sustainability of the production process. And, of course, the formwork-free production of concrete components can significantly reduce manufacturing cost. Now, this potential is to be developed using modern techniques such as computer-controlled 3D concrete printing.

The goal of the project was to automate long-established shotcrete technology and to incorporate it into a robot-controlled 3D injection printing process called "Shotcrete 3D Printing" (SC3DP). In addition to the development of the entire process technology from scratch, it was also necessary to create a suitable shotcrete whose properties could be adapted to the respective components and 3D printing process. MC was involved both in an advisory capacity and with the provision of suitable concrete admixtures. The SC3DP research is being conducted in the "Digital Building Fabrication Laboratory" (DBFL) at TU Braunschweig university of science and technology, a digitally controlled machining centre which enables coordinated operation of a 5-axis CNC portal milling machine and an integrated heavy-duty robot with a total of nine degrees of freedom. Here, various robot-supported techniques can be used for the production of geometrically complex three-dimensional concrete components, such as the combination of wet-spraying and milling. This enables additive and subtractive manufacturing approach and opens up new ways of constructing complex components with automated efficiency.

Project success at TU Braunschweig

Professor Viktor Mechtcherine and his team of engineers and researchers at the TU Dresden have been developing new technologies for 3D extrusion printing since September 2014. The working title for the first project read: "Feasibility studies for continuous and formwork-free construction processes by 3D forming of fresh concrete". In contrast to previous approaches, this research project focused on practical implementation directly on the construction site (in-situ concrete construction). The chosen technical basis for the equipment therefore consisted of established construction machinery, and the building materials employed were the concretes commonly used in solid construction.

Thus strictly aligned to current practice, the research approach was highly effective. To the delight of all involved, the concept won the Research category award at Munich’s 2016 Bauma, considered to be the world's largest construction machinery trade fair. During the project period, the interest of media and companies in this innovative technology grew so strongly that TU Dresden registered a trademark for the process dubbed "CONPrint3D® - Concrete Onsite 3D Printing" with the German Patent and Trademark Office in order to protect its research results. As the research project progressed, technical solutions for concrete delivery, the necessary print head and the long-distance robotics all underwent extensive development and evaluation. At the same time, concretes were specially developed and optimised for 3D printing and subjected to extensive rheological and mechanical investigations in their fresh and hardened conditions. The construction process itself was also analysed with a view to ongoing optimisation. The CONPrint3D® prototype site provided important data, facilitating economic appraisal of 3D concrete printing and proof of its technical feasibility.

When printing a complete example floor for an apartment building, the speed of construction for the walls proved to be 4 to 6 times faster than conventional construction methods, with further reductions in building time conceivable through an increasein layer thicknesses or speed of concrete placement. The calculations also revealed a cost saving of around 30% compared to the construction of the same floor using conventional masonry methods – not accounting for the fact that the building shell could essentially be erected without scaffolding and construction cranes.

Development of the new process is currently the subject of a follow-up project under the “ZukunftBau” umbrella, focusing on 3D printing based on foamed concrete, with MC foam generators integrated in the process.

MC – research partner

Research is also of great importance at MC. Indeed, the company owes much of its good reputation to the ongoing development of innovative construction chemical solutions. MC chemists, mineralogists and con-struction material specialists work hand-in-hand with technical product management and sales consultants worldwide. MC also regularly participates in national and international research projects and cooperates with universities and external materials testing institutes. Having produced the best results after extensive trials, an MC concrete replacement system specially developed for the research project was ultimately used for the concrete mix applied by the TU Braunschweig team.

The research project in Dresden also drew on the know-how of MC experts. Extensive preliminary and functional tests attended by relevant university personnel in MC's own laboratories in Bottrop led to the supply of a range of concrete admixtures including modified acceleration systems. In addition to providing advisory support of the research project, MC specialists were also asked to assess the commercial opportunities for the developed technologies on the world market.

Promising prospects

Although this technology is still in its infancy, it has already extensively proven its suitability on the international stage. The world's first fully printed office building opened in Dubai in May 2016. The United Arab Emirates are even pursuing a state-sponsored "3D Printing Strategy" – with the goal of introducing 3D printing for a quarter of all new buildings in the Gulf state by 2030. The Chinese company Win Sun is also already using an industrial-scale 3D concrete printing system in which the individual parts of standardised apartment buildings are produced in the factory and then simply supplied to the construction site for assembly.

Particularly topical is a project in Milan, Italy, which took the form of a single-storey demonstration building measuring some 100 square meters, constructed from 35 robot-produced modular elements. The flexible 3D printer required just 60 to 90 minutes for each of the individual elements, with the effective construction time for the entire building a mere 48 hours. 3D concrete printing is therefore well on its way to becoming an important factor in the global construction industry.