Mr. Kreft, your colleagues and you have conducted an extensive series of tests over the past few months. What was the goal?

We wanted to find out under which conditions processed AAC from construction and demolition waste can be reintroduced into production, technically, ecologically, and economically. In recent years, we had already developed a tentative requirements profile, but it reflected more or less only Xella’s perspective. This time, the challenge was to find a consensus between our ideal standards for varietal purity and what recyclers could realistically achieve; in other words, aligning requirements across the supply chain. Over a period of six months, we conducted hundreds of test castings with a wide variety of foreign materials.

How did you approach it?

First, we analyzed the incoming material: what types of typical foreign substances are found in it? We encountered a broad range: from tiles, ceramics, glass, and wood to plastics like PVC and polystyrene. We deliberately mixed these materials into our standard concrete formulations in practically relevant concentrations.

What were the results?

Our test series shows that typical foreign substances can be tolerated up to a clearly defined limit without impairing the manufacturing process or the quality of the end product. Our tests showed that, technically, the material performs very well. And we’ve backed all of this up with sound statistical analysis.

What does this mean going forward?

With these findings, we now have a first-required profile in hand. It defines for the first time which foreign materials are acceptable and in what quantities. This gives us a foundation for working with recycling companies, construction companies, and public authorities.

That sounds like you’re working toward a standard?

If we’re serious about a circular economy, we need more than good technology, we need common standards that everyone can rely on. That’s why we’re working together with Xella Germany as well as other AAC producers (via the German Bundesverband Porenbetonindustrie) and waste management companies to consolidate these requirements into a so-called DIN SPEC. This “pre-standard” will be finalized by end of 2025. It’s meant to become a shared technical framework that defines sorting accuracy and helps to define when waste-AAC ceases to be waste. Thus, it will contribute to increasing the recycling rate of AAC. Our plan is to convert the DIN SPEC into a full standard afterward.