Indaver Launches Circulith, Transforming Residual Waste Into A Certified Construction Raw Material

Indaver today launches Circulith, the brand name for the granulates it recovers from bottom ash. This bottom ash is the residual product of the thermal treatment of non-recyclable residual waste.

Circulith was granted end-of-waste status by OVAM (the Flemish Waste Agency) for use in concrete paving stones and concrete blocks. Independent certification body Procertus awarded BENOR certification^* for use in the construction sector to the concrete paving blocks produced by Belgian company Marlux-Stradus.

As a result, even more materials from Indaver’s waste-to-energy facilities can be put to high-value use. Ferrous and non-ferrous metals have already been successfully recycled from bottom ash for some time. Indaver intends to further scale up the ash treatment facility in Doel so that, in addition to its own bottom ash, it can also process bottom ash from third-party facilities. Waste management therefore goes beyond the safe treatment of waste. It also includes recovering energy and materials, replacing part of the primary raw materials used and creating an additional source of secondary raw materials.

Recovering raw materials on an industrial scale
Indaver’s ash treatment facility in Doel processes approximately 100,000 tonnes of bottom ash each year. This material results from the thermal treatment of around 400,000 tonnes of non-recyclable waste in grate incinerators. A further expansion of the processing capacity should ultimately make it possible to treat bottom ash from external waste-to-energy facilities as well.

Using a combination of washing, screening and advanced separation techniques, Indaver recovers metals, sand fractions and high-quality granulates, among other materials. At the same time, unwanted fractions and contaminants are separated in a controlled manner. In this way, the ash treatment process safeguards the product’s environmental quality and contributes to a quality-assured materials cycle. Each year, the process produces approximately 30,000 tonnes of aggregates that can be reintroduced into the economy.

Indaver therefore fulfils a threefold role: processor of non-recyclable waste, producer of energy from waste and supplier of secondary raw materials. This combination is a tangible example of how energy and material cycles can be closed.

Karl Huts, CEO of Indaver, says: “With Circulith, we demonstrate that the circular economy is not merely an ambition, but an operational reality on an industrial scale. By recovering materials from waste streams, we contribute to the more efficient use of available resources. This result did not come about by itself. Innovation in the circular economy requires technology, perseverance, collaboration and the courage to explore new paths.”

From bottom ash to a controlled construction raw material
The development of Circulith is the result of a journey spanning almost ten years. Since 2016, Indaver has invested in research, process improvement, certification and collaboration to enable high-quality applications for bottom ash granulates.

In 2022, Indaver and Marlux-Stradus jointly won the Port of Antwerp-Bruges symbiosis competition. In 2023, Indaver obtained an end-of-waste declaration, and in 2025 the use of the granulates in concrete paving blocks was approved under Marlux-Stradus’s BENOR certificate. Today, the incorporation of Circulith into concrete paving blocks is an operational reality.

Further strengthening circularity in concrete
Marlux-Stradus uses a limited amount of Circulith in the base concrete layer of concrete paving blocks. The visible facing layer remains unchanged. The application followed an extensive programme of testing and adjustments that began in 2022. Both the quality of the raw material and that of the final product are monitored through internal controls and independent supervision.

Ludo Monten, Innovation Manager at Marlux-Stradus, says: “With Circulith concrete paving blocks, we achieve two objectives at once: less extraction and less waste. By applying such solutions on a broad scale, public authorities can become a powerful lever for the circular construction sector of tomorrow.”

Fewer primary raw materials and a lower environmental impact
Using secondary mineral raw materials in construction products reduces the need for primary materials such as gravel and sand. This eases pressure on natural raw material reserves. Moreover, avoiding the extraction, processing and transport of primary materials further along the value chain can contribute to a lower environmental and CO₂ impact.

The launch is also an invitation to look ahead. A circular economy requires not only technological innovation, but also collaboration between the waste-to-energy sector, the construction sector, knowledge institutions, certification bodies and public authorities. Indaver therefore aims to raise awareness of Circulith as a substitute raw material and to explore new applications and markets together with partners.

Jo Brouns, Flemish Minister for the Environment and Agriculture, says: “Yesterday’s waste is becoming a raw material for new construction materials today. This is the circular economy as it should be: less waste, less extraction of new raw materials and keeping materials in our economy for as long as possible. Circulith shows very clearly how innovation can turn a residual stream into something valuable again.”

^* BENOR is a recognised Belgian quality label providing independent and reliable certification that a product or service complies with the applicable technical quality reference framework. Certified construction products undergo thorough internal quality controls supervised by an independent external inspection body.