Bio-Concrete from Knotweed & Crayfish: Turning Invasive Species into Building Material

Introduction

Concrete is one of the world’s most widely used materials—but also one of the top contributors to carbon emissions and ecological disruption. What if we could partially replace traditional concrete with something that helps heal ecosystems rather than degrade them? Brigitte Kock and Irene Roca Moracia, graduates of Central Saint Martins, are doing just that with a material they call bio-concrete. Made from two of the UK’s invasive species—Japanese knotweed and American signal crayfish—this innovative tile material transforms ecological liabilities into decorative surfaces, giving waste value and helping biodiversity recover. BrightVibes+2Design Nuance+2

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What Are Japanese Knotweed & Signal Crayfish, and Why Use Them

• Japanese knotweed (Reynoutria japonica) is a fast-growing plant introduced to the UK in the 1800s. It spreads aggressively, damages built infrastructure (e.g. growing through foundations), outcompetes native species, and is very hard to eliminate. BrightVibes+1
• American signal crayfish (Pacifastacus leniusculus) is another invasive species that has upset aquatic ecosystems in the UK. It outcompetes native crayfish, burrows into banks (erosion), and changes water chemistry. BrightVibes+1

Kock & Moracia’s idea: harvest or collect these invasive species (that otherwise are destroyed or disposed of), process them, and use them as raw material in place of some conventional components of tile-like finishes. The goal is both ecological (removing a harmful species) and material (creating a concrete-like alternative with lower fossil carbon, less quarry/extraction, etc.). BrightVibes+1

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How Bio-Concrete Is Made: Ingredients & Process

Here are the main steps and components:

Component	Role in Bio-Concrete
Knotweed ash	Acts as the binder element. The knotweed is incinerated or burned to ash, which replaces part of the cement or ash-binder functions.
Pulverised crayfish shells	Used as aggregate instead of conventional sand or crushed rock. Shells provide calcium (similar to limestone) and texture.
Water & gelatin	Used to help bind everything together, give workability, and enable curing without needing high-heat or high-energy curing processes.
Molds & curing	The mix is cast into molds (tile or panel shapes), cured (hardened) under ambient or low-heat conditions, and allowed to develop texture, coloration depending on the mix ratios and materials used. BrightVibes+1

A few additional points:

• The color and texture vary depending on the ratio of knotweed ash, shell aggregate, and whether raw root parts are included. Some tiles develop deep burgundy tones when knotweed root is included; others are paler or greenish depending on shell treatment. BrightVibes+1
• The finish resembles raw concrete or stone with natural variation—porosity, texture, veining, etc., which gives aesthetic richness. BrightVibes+1

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What Bio-Concrete Can & Can’t Do

What it can do:

• Works well for non-structural applications such as interior tiles, decorative surfaces, retail store materials, paneling, wall cladding in non‐load bearing settings. BrightVibes+1
• Offers an ecological benefit: helping incentivize removal of invasive species by giving them value rather than just being waste. Also reduces reliance on new quarry or mined aggregate. BrightVibes+1
• Can achieve varied aesthetics and finishes naturally, depending on the mix, without synthetic dyes or intensive processing. Lampoon Magazine

What it cannot (yet) do / challenges:

• Not yet certified for structural uses (load-bearing walls, foundations, beams). It lacks the strength, consistency, and lifetime data for those applications. Lampoon Magazine
• Durability issues: exposure to moisture, freeze/thaw cycles, wear & tear may degrade the material more than traditional concrete or stone if not sealed or protected.
• Regulatory hurdles: invasive species in the UK are often legally classified as invasive waste, which carries handling, disposal, and regulatory restrictions; these rules complicate using them as raw materials. Lampoon Magazine+1
• Scaling up: sourcing, processing, and ensuring consistent mix ratios and quality across batches is nontrivial. Also, industry acceptance, cost per unit, finish quality, and manufacturing scalability all remain limiting factors.

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Why This Matters & Broader Implications

• Circular & regenerative potentials: The material does more than “do less bad” — it regenerates by removing harmful species, reducing waste, and giving value to local ecological cleanup.
• Carbon emissions reduction: Since it replaces some cement (which is carbon-intensive) and uses waste/biological byproducts, overall embodied carbon is reduced.
• Design & aesthetics: Products that look and feel unique (texture, color variation) can appeal to interior design, luxury retail, architectural finishes, which helps drive demand and acceptance.
• Policy & waste law implications: Projects like this highlight contradictions in waste regulation—how invasive species are classified, how waste is handled/destroyed vs how it could be repurposed. Reclassifying or changing regulation could unlock many such upcycling opportunities.

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FAQs

Q1: Does using these invasive species harm ecosystems further?
If not handled properly, yes. For example, cutting knotweed improperly can spread it. The project works with removal specialists and ensures proper treatment (burning into ash, etc.). Lampoon Magazine+1

Q2: Is the bio-concrete biodegradable or does it break down?
Not fully. The project isn’t focused on biodegradability; rather it’s focused on creating a durable tile/surface that remains stable in interior conditions. Over time, with exposure, parts may degrade unless sealed. Lampoon Magazine

Q3: What scale is this at now?
It’s small scale — proof of concept, tile and finishes. Commissioned tile panels, prototypes for retail interiors (including a luxury brand’s program). Not yet mass-produced for large structural use. BrightVibes+2Design Nuance+2

Q4: How strong is it compared to regular concrete or stone tile?
Data on exact compressive strength varies depending on mix, but it’s less strong than structural concrete. For interior tile use, its strength is acceptable. Longevity and hardness relative to wear still need testing.

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Conclusion

The “bio-concrete” made from Japanese knotweed and crayfish shells is an inventive and powerful example of regenerative design: turning ecological threats into material opportunities. While it won’t replace concrete in every application, it opens a path toward building materials that do environmental good, not just reduce harm. As material science, regulation, and demand evolve, such approaches could become more common—where invasive species are removed, waste becomes resource, and built environments join the restoration of ecosystems.

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