With the Rammed Earth Robot on the Construction Site TU Braunschweig further develops old construction technology with additive manufacturing

It is climate-friendly, moisture-regulating, recyclable, easily degradable and a raw material that is available almost everywhere: clay. As a sustainable-ecological building material, it is now coming back into focus. Technische Universität Braunschweig is investigating how rammed earth building components can be manufactured with robotic support. In a project previously funded by the Zukunft Bau research initiative and now by the GOLEHM initiative, the Braunschweig scientists are now developing this process further in order to use additive manufacturing directly on the construction site.

Buildings have been made of clay for thousands of years. “Nevertheless, clay seems like a new building material to us. The knowledge about different construction methods and also the buildings themselves has unfortunately been partially forgotten,” says Joschua Gosslar. The research associate at the Institute of Structural Design (ITE) at TU Braunschweig would like to use the traditional knowledge of clay building methods and apply it to today’s production methods. In clay, Gosslar sees many answers for the building industry, which causes a large part of the world’s CO₂ emissions, for example in the production of cement, bricks and steel. “Clay is incredibly reversible. Components made of clay in a ‘mud house’ can be torn down after 100 years and spread in the garden, or reshaped and used to build a new house.”

From hand tampers to additive manufacturing

Clay has disappeared from building sites partly because of the high effort involved. Thus, many helping hands are needed for a rammed clay house. The old building technique is based on the layer-by-layer compaction of the clay in a formwork with the help of a hand-held wooden rammer. Formwork technology has since improved and automatic rammers have replaced hand rammers. However, the process is still manual and thus rather uneconomical compared to other building materials and techniques.

Joschua Gosslar himself recently completed the craftsman training course “Clay Construction Specialist” from the Dachverband Lehm and, among other things, worked on the construction of a high-bay warehouse made of rammed clay. “Rammed clay is an extremely luxury material, although the clay costs virtually nothing and is available almost everywhere. However, the processing is expensive. About two thirds of the costs are caused by the formwork, which has to be very robust to withstand the ramming pressure.”

Entire production steps are omitted

The digitally controlled technology of additive manufacturing, which ITE is also researching with the materials concrete and steel in the collaborative research centre “Additive Manufacturing in Construction” (AMC) of TU Braunschweig and TU Munich, could not only ensure higher precision and consistent quality here, but also be more productive and thus more economical. “In additive manufacturing, the material is built up layer by layer, without preceding mould construction or subsequent forming processes. This means that entire production steps such as shuttering and striking in concrete construction can be omitted. In addition, completely new shapes are possible that utilise the material more efficiently. Automation and individual shaping are therefore no longer a contradiction in terms for the building industry, and additive manufacturing has the potential to bring together the goals of economy and ecology,” explains Professor Harald Kloft, head of ITE and spokesperson for the AMC Collaborative Research Centre. “We are also making it easier for planners to choose sustainable materials and innovative construction methods.

Compacting rammed clay with robots and slipforms

The researchers have therefore developed a travelling formwork and compaction tool that is operated robotically. The compaction unit consists of a vibratory plate and pneumatic rammers that travel with the formwork element and work their way up layer by layer. The Digital Building Fabrication Laboratory (DBFL), the institute’s large 3D printer, is used for this. “The great thing about rammed clay is that you can remove the formwork immediately after compaction. The material does not need to cure for initial strength, like concrete for example. Therefore, in our project, the formwork only sits where it is also compacted and then it is moved on. So it is an active sliding formwork,” explains the clay expert.

Based on this preliminary work, the scientists want to further develop the robotic rammed clay fabrication for construction site production in the new project. “We want to reduce the whole setup so that it can be used in a mobile, digital manufacturing process,” explains Joschua Gosslar.

The research project is supported by GOLEHM, an association that wants to make clay construction attractive again by preserving the old techniques and giving (solid) clay construction a future with innovative concepts.

Mobile production unit

Together with the Institute of Building Materials, Concrete Construction and Fire Safety (iBMB) and the Institute of Machine Tools and Production Technology (IWF), the Institute of Structural Design wants to optimise clay construction techniques and create a robotic unit that can be used on site at the construction site. “Instead of prefabricating the clay, local material should be used and an automated mixing, conveying and feeding process should be developed,” says Joschua Gosslar. “One of the appealing aspects of clay building is that clay is available as a building material in many places. Unlike concrete, this building material does not require an elaborate infrastructure and can be quarried locally without having to transport it over long distances.”

First, the scientists have to design the mobile production unit: The centrepiece will be a mobile 3-axis gantry robot that can be moved from construction site to construction site. In addition, there will be the end effectors, the robot’s hands, so to speak, and a material feeding unit so that the building material is applied very precisely. The local raw material will also be checked and optimised on site so that the excavated earth becomes usable building material.

At the end of the two-year project, there should be a demonstrator with which the researchers also want to construct part of a building.

Project data

In addition to the Institute of Structural Design at TU Braunschweig, the Institute of Building Materials, Concrete Construction and Fire Safety (iBMB) and the Institute of Machine Tools and Production Technology (IWF) are involved in the mobile, robotic rammed clay project. The project is being funded for two years until November 2024 with around 400,000 via the GOLEHM initiative.

GOLEHM – Initiative for clay building and sustainable circular economy

The GOLEHM alliance brings together active partners from science, the building industry, municipal sponsors and society who are committed to climate-friendly, sustainable building with clay. GOLEHM was launched in 2020 by the Saxony-Anhalt State Office for the Preservation of Monuments and Archaeology, the Martin Luther University Halle-Wittenberg and the Berlin-based engineering office ZRSI. In the meantime, the network has grown to include a large number of regional and supra-regional actors from various areas of expertise who want to further develop clay construction and bring it to widespread market use as a climate-friendly building material. Within the framework of several projects that have been initiated so far, important basic principles are being researched in order to bring the building material clay out of its niche.

Further information:
www.golehm.de