Autoclaved aerated concrete and calcium silicate units are good building materials because both have high strength and robustness, and insulation properties (heat protection and/or sound insulation). Nevertheless, CO2 emissions are caused. We therefore want to significantly improve the CO2 footprint of our products. Our approaches: high resource efficiency, decrease energy consumption on our plants, a long lifespan for our products, and high circularity.

Increasing recycling rates

Our mission is for every building to serve as a storehouse of raw materials for the buildings of tomorrow. We want to be a leader in reusing AAC construction leftovers. Our goal is to increase the recycling rate for autoclaved aerated concrete (AAC) to 20 percent of the annually generated AAC construction- and demolition-waste by 2030 in Germany. According to current forecasts, this corresponds to an annual volume of around 200,000 tons. A wide variety of projects are currently underway to achieve this. Their focus is on fully reprocessing building components and using the recovered materials into the production of new building materials. (More details, for example, here.)

Improving circularity

At the same time, we are researching ways to adapt the formulations of our products without compromising on quality. In this way, we use and reuse raw materials as efficiently as possible. For example, by making greater use of autoclaved aerated concrete powder In the case of calcium silicate units, we believe that there are two possible solutions: reducing the lime content and reducing the energy input, i.e. changing the energy source used for steam curing. We are also pushing product innovations and focusing on open innovation projects (read more here).

Alternative products

We wouldn't be Xella if we didn't also address the question of the building materials of the future. In addition to optimizing our existing products, this is also the mission of our Technologie- und Forschungsgesellschaft mbH (T&F). The focus here: finding CO2-minimized approaches. "The search for alternative raw materials inevitably leads to alternative products," Torsten Schoch, managing director of T&F, says. Cement-free and/or lime-free autoclaved aerated concretes will not be available in the short term according to the current state of scientific knowledge.

That is why T&F is also looking at alternative low-CO2 approaches such as the use of biogenic raw materials (hemp and bamboo) to reduce the use of cement and lime.An exciting approach here is, for example, a stone with a bamboo content that could even offer greater strength than autoclaved aerated concrete and with only slightly higher thermal conductivity. At the same time, it would also be possible to recycle residual plastic from the world's oceans as a raw material of the future.

"In all these research projects, we pay particular attention to resource conservation, i.e., to using the least possible amount of renewable raw materials. At the same time, the advantages of autoclaved aerated concrete and calcium silicate bricks that are known today must not deteriorate, and the durability of the building materials must continue to be guaranteed," says Schoch. However, it will still be a while before solutions that are ready for use can be expected here.