Green concrete from organic waste: a game changer for Africa

Dr Wolfram Schmidt from the Bundesanstalt für Materialforschung und -prüfung (BAM) has been researching sustainable building materials since 2009. Together with colleagues from Ghana and Nigeria, he developed a pyrolysis system at Koforidua Technical University (KTU) that uses biomass to produce materials for cement and concrete.

The approach builds on experience gained from the construction of a model home between 2016 and 2018 using cassava husk ash as a binding agent to produce concrete. The approach earned Schmidt and his partners the German-African Innovation Incentive Award in 2018. Current research focuses on further developing this technology so that it can be used throughout Africa, directly within village communities as part of local construction projects.

Cement production accounts for around 8% of global CO₂ emissions, most of which result from the chemical reaction involved in burning limestone rather than energy consumption. Africa’s urban population is also growing rapidly, with OECD estimates predicting a doubling in size from 700 million to 1.4 billion people by 2050.

This means that demand for housing – and therefore for concrete – is set to skyrocket. If the industry continues to operate at current levels, this will present serious climate-related consequences. A more emission-friendly alternative is therefore urgently needed.

The idea of using natural materials in construction has been around for a long time. The benefits of using natural materials in construction were recognised as far back as Roman times, with volcanic ash used to produce durable mortar. Wolfram Schmidt and his team of colleagues at KTU used this concept of sustainability as a hook to develop a compact, cost-effective pyrolysis unit that is easy to replicate and is based on scalable technology. The unit carbonises food waste in the absence of oxygen, thereby avoiding the release of large volumes of CO₂ into the atmosphere.

From the very start, the project set out to be sustainable in a number of ways. GIZ organised training for 100 local students, who acquired specialised knowledge of producing low-carbon cement and applied this knowledge in practical experiments. Some of them aim to investigate which material is best suited to producing efficient active carbon.

BAM and its partners researched the materials required for the entire production process, with a view to passing on this knowledge to local companies at a later date. The project partners successfully completed the facility in September 2023.

‘African problems require African solutions,’ says Wolfram Schmidt. The use of agricultural by-products has demonstrated how waste can be turned into a valuable resource. Close collaboration between the research sector and industry has meant that the pyrolysis system has been developed not only as a research project but also as a marketable, practical solution. The project managers are already navigating the future, with Schmidt at the helm: ‘In an ideal world, this system would be mounted on a pick-up truck, so that it could produce and deliver at the same time.’