Building sustainably with reusable concrete slabs

Carbon concrete panels developed by the ZHAW are being used in building construction for the first time. This innovation not only enables considerable CO2 and material savings, but also a flexible system with reusable components.

Designing, constructing and planning customized buildings on the computer is nothing new. However, for the first time, filigree yet resilient prefabricated elements are available for building construction: Carbon fiber-reinforced concrete panels. "Our carbon concrete construction system works in a similar way to Lego, but like a modern version of it, with tailor-made components," explains ZHAW researcher Josef Kurath, who developed the flexible construction method. It offers several advantages, as illustrated by a 120 square meter pavilion in Winterthur, which was built using this flexible construction system from the ZHAW. This so-called innovation laboratory serves as an information and event venue for sustainable construction.

Flexible modular system for building construction

The carbon concrete panels used for this are manufactured, processed and cut to size in the factory. Using plug-in systems, they can be assembled into building elements in the factory and installed on the construction site in the shortest possible time. "This results in much shorter construction times, which is a particular advantage for urban construction sites," emphasizes ZHAW professor Josef Kurath. In addition, buildings can be easily adapted or extended on site." If necessary, the innovation lab could be expanded or dismantled with little effort and reused for another building. This is made possible by an innovative sharing model for carbon concrete slabs from building materials producer Holcim. While around 90 percent of the concrete cannot be directly reused when dismantling a conventional building, the opposite is true for the new construction system: around 90 percent of the material and the added value contained in the component can be reused. In view of the fact that cement alone is responsible for eight percent of global greenhouse gas emissions and that Switzerland is one of the countries with the highest cement consumption per capita, this is a remarkable factor.

Carbon fibers at the heart

These carbon-reinforced panels are not only reusable and extremely durable. Their production also has less impact on the environment than reinforced concrete. "Thanks to the new lightweight construction method in concrete, we reduce the CO2 footprint by a factor of two to four and save up to 75 percent material compared to conventional construction methods," explains Josef Kurath, ZHAW professor and co-founder of the ZHAW spin-off CPC, which developed the filigree, resilient CPC concrete slabs (Carbon Prestressed Concrete). "Prestressed carbon fibers and concrete complement each other perfectly. Carbon absorbs the tensile forces and concrete absorbs the pressure and transverse forces." Compared to conventionally reinforced concrete slabs, CPC slabs do not crack under load and bounce back undamaged. They are also three to four times thinner than conventional materials without losing any of their load-bearing capacity. The ZHAW civil engineer sees the greatest potential of the patented CPC panels in the fact that they can be produced industrially, cut to size and do not rust. "We are the only company in the world that can industrially produce concrete slabs that are biaxially prestressed with carbon fibers."

Construction kit to order

The CPC slabs are currently being produced in Holcim’s first CPC plant in Germany. The building materials producer has designed the concrete for these innovative construction elements without steel reinforcement. The carbon fibers are produced by the ZHAW spin-off CPC in Döttingen - in future with bio-based carbon from renewable raw materials such as algae or cellulose, which does not require any crude oil. "The panels developed will also be produced in this country in the future and the new construction system will be widely used in building construction - the Swiss market is predestined for this," says Josef Kurath. For the patented construction system, a great deal was invested in the development of panel connections. These connections consist only of the panels themselves and a conventional mortar, meaning they do not require any adhesive or steel components. According to the ZHAW researcher, research is currently being carried out into optimizations for sound and fire protection as well as special constructions for an earthquake-proof building core or large-area ceiling connections. "In future, the individual ceiling elements should interlock with each other like a zipper, so that almost endless levels are possible horizontally - without additional connecting elements."