From Rice Husks to Concrete

_{A concrete component made of recycled aggregates and rice husk ash, with rice straw insulation (Credit: Fraunhofer WKI)}

High-performance building materials made of building rubble and plant waste could make the construction industry more sustainable, their creators have said.

Also offering a way to speed up reconstruction in war-hit countries such as Ukraine, the materials were developed as part of the ReMatBuilt project at the Fraunhofer Institute for Wood Research in Braunschweig, Germany.

The building sector is one of the world’s largest consumers of natural resources, but also produces huge amounts of waste that needs to be recycled. This was the starting point for Professor Libo Yan and his team, which created the materials from demolition waste and plant production residue with partners in Germany and China.

The team used concrete and masonry waste, as well as agricultural waste, to produce recycled concrete. Components were reinforced with plant-based natural fibres such as flax and supplemented with wood chips from forestry waste.

Ash from burnt rice husks was used as a “more than adequate” cement substitute, said Professor Yan, offering a way to avoid high carbon dioxide emissions from conventional materials.

“The idea of recycling construction materials and experimenting with alternative materials from nature is not new. What makes our project unique is its holistic approach,” Professor Yan said.

“We combine our knowledge of the methods and properties of the different materials in order to understand their chemical, physical and mechanical performance from the micro- to the macro-scale. This allows us to achieve a very high technology readiness level, which is an important aspect for practical application.”

The team is also developing insulating materials made of plant-based waste products such as sawdust, rice and wheat straws, instead of crude oil-based plastic, mineral and glass wool, or wood fibres. The new sustainable insulation boards can connect to the finished concrete components to form insulated walls.

The researchers also designed composite systems that allow recycled concrete, combined with laminated veneer and cross-laminated lumber, to be used as timber-concrete composite floor slabs. The hybrid construction elements reportedly have “impressive” mechanical and heat protection characteristics.

By using waste materials in a sustainable new way, the products could have “immense potential” in warzones, the Fraunhofer announcement said.

“Our work has the potential to make a significant contribution to the reconstruction of Ukraine,” said Professor Yan. “The country is also rich in natural resources and one of the world’s largest exporters of agricultural raw materials, such as grains – wheat, corn and rice.”

He added: “We are currently working hard on putting our results into application. With local industrial partners, we can significantly help the people in Ukraine to reconstruct their country quickly, economically and sustainably. We can do this with recycled concrete components and corresponding insulation made of natural materials that are all abundantly available on location.”

The project is funded by the German Federal Ministry of Education and Research (BMBF) as part of the National Bioeconomy Strategy.