Design of agro-waste: hulls, bagasse and straw transformed into efficient building materials

Design of agro-waste: hulls, bagasse and straw transformed into efficient building materials

The concept of upcycling is to take an item that would be considered waste and improve it to make it useful again, adding value and new functionality. It is a common word in several industries, such as fashion and furniture. In civil construction, this concept can also be integrated, recirculating waste generated by the industry itself or even bringing what would be rejected by other industries to be treated and incorporated into constructions. This is the case of the transformation of agricultural waste into building materials, bringing new use to scrap, reducing the use of raw materials and creating products with excellent characteristics.

Duplex on the hillside / MWArchitekten.  Image © Adolf Bereuter
Duplex on the hillside / MWArchitekten. Image © Adolf Bereuter

Rethinking the current linear economic model – where production is directly linked to the extraction of natural resources and their disposal at the end of their useful life – has been a prominent topic among the debates around a more sustainable future. According to the principles of the circular economy, organic waste from cities and countryside could be diverted from landfills, irregular disposal or incineration to become the raw material for the creation of products before being reinjected into the life cycle at the end of their useful life. .

This includes reusing corn cobs, sugar cane bagasse, rice straw, wheat and soybeans, peanut shells, bananas, sunflower seeds, cellulose and many more. others, depending on the culture of the place. Constructions using straw have already been explored in this article, where leftovers from grain production, usually wheat, rice or barley, can be bundled together to create very effective seals and insulation. Several studies and experiments have been carried out with this agricultural residue, qualifying it as a potential material for the construction of walls, with good thermal, acoustic and even structural characteristics.

Refuge II / Wim Goes Architectuur.  Image © Filip Dujardin
Refuge II / Wim Goes Architectuur. Image © Filip Dujardin

In regions closer to the tropics, for example, a product with a high waste content is coconuts. Its fibers, whether ripe or not, have several uses. They can be added to concrete mixes or, in some cases, become cement floor brick reinforcements. This is the case of this Scientific Research in the northeastern region of Brazil, whose aim is to meet the demand for new construction in low-income communities and to increase the production of an alternative brick reinforced with coconut fibers, capable of contributing mainly to recycling green, ripe coconuts in urban areas and rural dumps. Coconut fiber can also be used as thermal insulation, as in Casa Parasita, by El Sindicato Arquitectura, where a 12 centimeter layer was used between the exterior sheets and the interior OSB finish.

Casa Parasita / El Sindicato Arquitectura.  Image © Andrés Villota
Casa Parasita / El Sindicato Arquitectura. Image © Andrés Villota

But waste does not have to come only from the earth to be recycled. Mariculture waste in southern Brazil has the potential to be used as an aggregate in the production of concrete, to avoid depositing it in sandbanks and on the seashore or on any terrain. The material replaces much of the sand and concrete used to produce the blocks, making them lighter than common blocks and with better acoustic results. Another example comes from Mexico, where trials have been conducted using leftover agave from tequila production to produce wood substitutes.

A sample of the wood substitute from a tequila by-product and recycled plastic.  Image © Plastinova via phys.org
A sample of the wood substitute from a tequila by-product and recycled plastic. Image © Plastinova via phys.org

Filipino-Ghanaian architect Mae-Ling Lokko has developed in-depth research on the concept of Agrowaste design or “design with agro-waste” and the use of these biomaterials in architecture. As Marília Matoso writes in her article on the subject, “It has the potential not only to fill gaps in the product lifecycle, but also to stimulate forms of generative citizenship through upcycling.”

Housing unit for musicians / AUAR.  Image © NAARO
Housing unit for musicians / AUAR. Image © NAARO

Also there are several academic researches which demonstrate that the reuse of agricultural waste not only helps to address the problem of pollution caused by the exploitation of conventional building materials, such as cement, but also the environmental concern of waste disposal in landfills. These created materials can also have commercial viability and characteristics that allow them to be compared to any other traditional product. In 2017, global engineering company ARUP developed a full investigation possibilities of transforming agricultural waste into efficient building materials. Titled “The Urban Bio-Loop: Grow, Manufacture and Regenerate”, it lists the main uses as follows:

  • Partitions and interior finishes: flat plates – with decorative layers if necessary. Various organic waste streams can be used for applications such as bagasse, pulp, seeds, stems or peanut shells. These products are generally characterized by a low specific weight – they are therefore easy to handle – and are rigid enough to guarantee adequate resistance to impact.
  • Furniture: Natural fibers and small residual particles can be molded into complex shapes for chairs, tables and more generally for any interior application. A variety of surface finishes provide strong aesthetic appeal.
  • Acoustic absorption: high porosity materials – such as bio-foams – can be obtained from soy residues. In addition, fibers of different types can be combined to create an insulating material with good sound absorption properties.
  • Thermal insulation: various natural fibers obtained from agricultural crops can be used. These offer low thermal conductivity and some of them are characterized by the good performance of spruce and are water repellent, such as potato skins and cork.
  • Rugs and carpets: based on a wide variety of natural fibres, such as those obtained from banana or pineapple harvest residues, and other flexible, resistant and light fibres.
  • Envelope systems: To some extent, natural fibers can be combined with biopolymers to obtain rigid finished products that can be used for both interior and exterior applications.
The Green Island Community Center / Estudio Cavernas.  Image © Denis Amirtaraj
The Green Island Community Center / Estudio Cavernas. Image © Denis Amirtaraj

Materials can be used almost raw, with little processing, as is the case with the sugarcane straw that covers the roof of the Green Island Community Center in Thailand. In the project by LCA Architetti and luca compri architetti, ecological materials play a leading role. According to the responsible architects, “nature guides the choice of building materials: wood for the basic structure, rice straw and cork as insulation; the interior finishes and furniture are in stone and oak wood.”

The House of wood, straw and cork / LCA Architetti / luca compri architetti.  Image © Simone Bossi
The House of wood, straw and cork / LCA Architetti / luca compri architetti. Image © Simone Bossi

Linen, for example, can be used to create thermal insulation, as in the case of the Hemma house, by stek architecten, but it can also form boards, such as those used in the construction of the case study houses Vasterival.

Hemma House / stek architecten.  Image © Bram Delmee Photography
Hemma House / stek architecten. Image © Bram Delmee Photography

the Organic House project in Denmark has drawn attention to agricultural industry waste such as sheep’s wool, grass, straw and seaweed, turning it into valuable building materials. The house is almost completely biodegradable and has minimal impact on the environment. Its main function, however, is to demonstrate how the incorporation of waste can create aesthetically interesting and above all efficient buildings.

Considering the possibilities and supporting research and experiments on the circular economy and the reuse of waste in such a large and resource-intensive industry as civil construction can be a good way to achieve global sustainability goals and seek a more environmentally friendly future.