As researcher, designer and MIT professor Caitlin Mueller once said, “The greatest value you can give to a material is to give it a load-bearing role in a structure.” Load-bearing components – foundations, beams, columns, walls, etc. – are designed to resist permanent or variable forces and movements. Similar to the bones of a human body, these support, protect and hold everything together. To fulfill that indispensable function, they must be made from materials with outstanding mechanical properties, which explains the prominence of cement and steel in structures. However, their high performance comes at a high cost: together, they account for 15% of global CO2 emissions. This makes us wonder, is it possible for structural materials to be truly sustainable? We know solutions like greener versions of concrete already exist, but there are many other alternatives to explore. And sometimes, the answer is closer than we expect; in the earth beneath us and the nature that surrounds us.
Naturally derived materials – also called bio-based or bio materials – like mycelium, hemp, straw and cork have long been utilized in the architecture and design industry. Despite their continuous development, these tend to be associated with cladding and finishes rather than with strong, durable and load-bearing systems. But, along with new technologies, research has advanced tremendously, resulting in bio material innovations that show great potential in structural applications. Below, we present three promising examples that replace steel, concrete and limestone. Although these are in experimental or early stages of development, they certainly contribute in paving the way towards a more sustainable future built environment.
Discarded tree fork joints
Tree forks are the part of a tree where the trunk or branch splits in two, forming a Y-shaped piece. Although exceptionally strong, these are rejected in timber construction because they are not straight. Most structural joints, on the other hand, are made of highly emission-intensive steel. In this context, a group of MIT researchers, composed of Building Technology Program Professor Caitlin Mueller and her Digital Structures group, have come up with an innovative approach. Considering architecture is filled with Y-shaped nodes where straight elements come together, they have developed load-bearing joints made from discarded tree forks. Following the timber construction trend that seeks to replace concrete and steel components, this opens up an opportunity for further sustainability gains through the use of irregular tree sections. Normally, these are burned or ground up, releasing the carbon trapped in the wood into the atmosphere.
Tree forks are naturally engineered structural connections that work as cantilevers in trees, which means that they have the potential to transfer force very efficiently thanks to their internal fiber structure. – Caitlin Mueller
The strategy is to upcycle these “waste” materials by using them in construction as structural components. How? With advanced digital and computational tools, it is possible to distribute discarded tree forks among Y-shaped nodes in architectural designs. These are allocated in a way that maximizes the use of the inherent strength in the wood fiber and then reallocated instantly if the architect changes the design. To guide the cutting process, researchers use a custom algorithm that calculates the cuts needed to make a fork fit into its assigned node. And to put it all together, one must simply follow the instructions: “Computer-driven robotic machining adjusts and marks the tree forks for easy assembly with straight wooden elements.” In the future, the team plans to work with larger material libraries, such as multi-branch forks, and incorporate new scanning technologies.
3D-printed mycelium columns
Fungi, the most abundant group of soil microorganisms, play several significant roles in ecosystems, from being an important food source to providing nutrients to plants. Recognizing these advantages, Blast Studio has developed a way of 3D printing a two-meter-high structural column – known as the Tree Column – out of waste and mycelium, Fungi’s root system. The production process begins with collecting discarded paper coffee cups and boiling their shredded pieces in water to produce a sterilized pulp. Mixed with the mycelium, this creates a biomass paste that is later 3D-printed to form 10 separate modules, which are then stacked one on top of the other and fused together with more mycelium.
The Tree Column’s ridged, undulating shape is algorithmically designed to retain moisture and protect from airflow, recreating an ideal climate for mushroom growth. But the design also has a structural purpose; thanks to the material’s elasticity, the column is lightweight and good in compression and flexion. Once it is solidified, it achieves a similar structural capacity to medium-density fiberboard (MDF), meaning the mycelium can ultimately substitute concrete in small buildings. Therefore, the technology is able to create, without formwork, complex shapes that optimize performance while replacing traditional structural materials. Blast Studio currently aims to scale up the technology to print a pavilion and hopes to construct buildings in the future, which would potentially allow cities to grow architecture from waste while providing food for their inhabitants.
Algae-grown limestone
Portland cement, the most common type of cement, is made with quarried limestone, which is burnt at high temperatures and accounts for a large part of the material’s greenhouse emissions. With that in mind, a research team from the University of Colorado Boulder has created biologically grown limestone that could potentially make cement production carbon neutral (or even carbon negative). The idea came about when Wil V. Srubar, who leads the Living Materials Laboratory at CU Boulder, observed in coral reefs how nature is able to grow its own durable, long-lasting structures from calcium carbonate – a main component of limestone. Along with his team, he began to cultivate coccolithophores, single-celled algae that, through photosynthesis, can sequester and store CO2 in mineral form. With sunlight, seawater and dissolved carbon dioxide, these microscopic organisms produce the largest amounts of calcium carbonate on the planet.
If all cement-based construction around the world was replaced with biogenic limestone cement, each year, a whopping 2 gigatons of carbon dioxide would no longer be pumped into the atmosphere and more than 250 million additional tons of carbon dioxide would be pulled out of the atmosphere and stored in these materials. – Kelsey Simpkins, University of Colorado Boulder
In this way, algae-grown limestone becomes an eco-friendly alternative. And because the method involves using concrete as we know it, it can already be used in structural applications on a mass scale. Essentially, it enables the same mechanical properties and load-bearing capacity of concrete, but with an ability to mitigate many of the harmful environmental effects generated by traditional cement. Looking ahead, the next steps involve increasing production to move towards commercialization, but the possibilities are already clear: this homegrown version of limestone creates an opportunity to transform future structures into carbon sinks, as well as to “improve air quality, reduce environmental damage and increase equitable access to building materials around the world.”
To replace structural emissions-intensive materials, bio-based alternatives must be affordable and easy to produce. But regardless of the upcoming challenges, they open endless possibilities; hand in hand with new technologies, it could only be a matter of time for these to translate into a healthier built environment.
This article is part of the ArchDaily Topics: The Future of Construction Materials. Every month we explore a topic in-depth through articles, interviews, news, and projects. Learn more about our ArchDaily topics. As always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.
