Mollusk Shells Relive as Construction Biomaterials

In the natural kingdom, where mortgages are nowhere to be seen, there are many tenants that build their own house and carry it on their backs. We are talking about mollusks such as mussels, oysters, clams, or sea snails, which form hard shells to protect them from predators and the elements. Statistics suggest that up to ten million tons of bivalve shells are discarded yearly. These structures are rich in calcium carbonate and are beginning to be used as new biomaterials for construction.

Although it has attracted renewed interest in recent years, this approach is far from a modern invention. For example, tabby concrete - a term of African origin - was used centuries ago in Muslim Spain. This material used lime from burnt oyster shells mixed with water, ashes, sand, and crushed oyster shells. However, the rise of the circular economy has brought these solutions back to the forefront, this time under the name of blue bioeconomy, in reference to the aquatic resources used.

In this article, you will learn about some of the new applications of these biomaterials in construction and other sectors:

• Bioconcrete
• Marine slabs
• Porous sidewalks
• Furniture for restaurants
• Helmets for fishing workers

Bioconcrete from invasive species

We have already discussed bioconcrete "spruced up" with bacteria or organic waste such as beets or carrots. In this case, two graduates from Central Saint Martins School in the United Kingdom have developed a material along these lines, but with two invasive species in their sights: the signal crayfish, which has taken over European rivers, and Japanese knotweed, which grows uncontrollably and destroys walls and pavements. The crayfish shells give the bio-concrete its strength, while the plant matter of the knotweed gives it the eye-catching textures visible in the resulting tiles and other pieces. Don't run to the store to buy them, however, because they are not yet on sale.

"Marine" slabs  

Maybe, among their many uses, the tons of oyster shells and other mollusks that end up in landfills will one day become part of your home. That's the approach of a Korean design studio that has launched a new line of slabs based on shells and natural binders that require no heat – pouring the mixture into a mold is enough to obtain the terrazzo-style pieces. For the time being, they are used ornamentally since the absence of heat treatments results in lower resistance of this biomaterial with applications in construction.  

Porous sidewalks to prevent flooding

Climate change has multiplied extreme weather events such as flooding. In the case of cities, impermeable sidewalks and asphalt can turn these precipitations into real torrents that easily overflow drainage systems. Under the name CIRCLE, the European Union is promoting a new project with two British universities and several French partners to produce porous concrete that absorbs rainwater. Again, the key to this sustainable building biomaterial lies in the use of mollusk shells. It will also have the advantage of filtering water before it penetrates the subsoil.  

Furniture made from restaurant waste

Imagine a stool or a table made from the waste of the restaurant where you have just dined. Well, that's what they have done in a Swedish restaurant in Gothenburg. There, a designer has used oyster shells, rice starch, and collagen from fish scraps to make a stool that can double as a side table. The terrazzo-style finish is like the marine slabs mentioned above. Incidentally, even the leftovers from the process are used to produce chopstick supports.  

Helmets for fishing workers emulating scallops

It is not strictly a biomaterial for construction, but the helmets for fishing workers launched in Japan exemplify the new blue bioeconomy. In the fishing village of Sarufutsu, large accumulations of scallop shells from the fishing industry were an ecological problem. A plastics manufacturer has combined this material with recycled plastics to create the new helmet or "shellmet", which also leverages the principles of biomimetics – adopting the shape and grooves of scallop shells improves their strength by 30%.  

In addition to all these examples, we cannot fail to mention one of the pioneering initiatives in the field of biomaterials for construction from mollusks. We are talking about the Biovalvo Project, a building in Galicia starring the shell of one of the most common molusks on its coast: mussels.

Source:

• MDPI
• Dezeen
• Universidad de Tyndall