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25.04.2018Sustainable Concrete Made with Coconut, Rice or Cassava
What makes concrete both strong and sustainable at the same time? The Bundesanstalt für Materialforschung und -prüfung (BAM) is presenting its cooperation with African colleagues at the Hannover Messe because many ideas for basic research on sustainable concrete come from German-African cooperations. BAM scientists are investigating to what extent vegetable substances could be used instead of chemical or mineral additives in concrete. The main focus of the research is on residues from agriculture.

Concrete production requires a lot of energy and produces large amounts of climate-damaging carbon dioxide because cement clinker must be burned at very high temperatures and the chemical reaction is accompanied by high carbon emissions.

Cement clinker used as a binder in concrete is an essential component of cement. Therefore, the reduction of cement clinker is a starting point in the search for sustainable concrete: Which organic substances could replace clinker or use it more effectively and in such a way that important concrete properties e.g. flow behaviour, strength or durability remain unaffected?

Renewable raw materials for the construction industry: coconut fibres, acacia juice or cassava peel

"We are experimenting with coconut fibres, acacia juice and cassava peel, among other things, and check the resilience of organic concrete compared to conventional mixtures," explained Dr. Wolfram Schmidt from BAM’s Technology of Construction Materials division. Suggestions about which vegetable substances are worth experimenting with often result from cooperations with African colleagues. One tip that came from Nigeria is cassava.

Cassava, also called manioc, is a staple food in the West African country, which is the largest producer of this plant worldwide. Its starchy tuber is edible, but the residual peel occurs in large amounts. Concrete is a building material that is in high demand in Nigeria, and readily available raw materials are sought for its production.

Cassava peel is a suitable raw material for concrete in two respects:

The residual starch adhering to the peel can be extracted and used as an additive to improve processing properties of concrete so that cement can be used more effectively.

When the peel is subsequently burned, the high reactive silica content enables the ash to be used as a sustainable cement substitute and improve the eco-balance compared to conventional concrete.

Thus, chemical additives and mineral cement substitutes can be obtained simultaneously.

The use of cassava peel has yet another advantage: Combustion energy released in ash production can be used to manufacture bricks for example.

Learning from Africa – for more sustainable concrete production in Germany

Though no cassava grows in Germany, the construction industry is also looking for possible new, sustainable raw materials for concrete production here and in other Western countries as well. "We will be able to transfer a lot to highly technical countries from our basic research and experience gained by working with our African partners," said Wolfram Schmidt. Vegetable components may even replace chemical additives in high-performance concrete in the future. Sustainable use of agricultural residues in the construction industry would not only be a contribution to environmental protection but also a potential additional source of income for farmers.