In a quiet Tainan workshop, a team of architects and designers is turning oyster shells into low-carbon bricks — challenging the global construction industry to rethink one of its most polluting materials.

STORY AND PHOTOS BY CORY HOWELL HAMADA AND LILLYGOL SEDAGHAT

Inside a traditional four-story house in Tainan, a new wave of innovation is taking shape. The space, cluttered with bags of plaster and boxes of dried coral, houses a laboratory where a local design company, C-Cube Lab, is crafting construction bricks from an unlikely source: oyster shells. It’s a small but striking contribution to the growing movement for sustainable materials.

“Each of these bricks uses 30% oyster shell,” says C-Cube Director and architecture professor Liou Shuenn-Ren. “It reduces carbon emissions by four kilograms per brick. Our target is reducing the use of concrete and cement.”

Originally established as a research lab housed in Tainan-based National Cheng Kung University’s School of Architecture, C-Cube specializes in recycling various forms of waste into construction materials. The company now operates out of a narrow alley house that serves as both showroom and workshop. Former living rooms display modular furniture; the kitchen, now used for mixing prototypes, is what Liou calls a “material kitchen.”

“I think it’s the heart of the whole research,” he says.

According to the World Economic Forum (WEF), concrete is the most widely used constructed material, with cement — the key binding agent — accounting for a staggering 7% of global carbon emissions alone.

As annual consumption of cement approaches 30 billion metric tons and is projected to rise more than 40% by 2050, companies like C-Cube see an opportunity. By substituting cement and concrete with locally sourced waste such as oyster shells, discarded bricks, and reservoir silt, the company hopes to carve out a lower-carbon path for the construction industry.

“I strongly believe the key is material,” Liou says. “When we talk about sustainability, the root is materials. More specifically, the innovation of material.”

A push to replace cement

Traditional concrete is made by combining aggregate, usually gravel and sand, with water and cement. Cement acts as the glue holding the ingredients together. Though it makes up only 7% to 15% of a typical concrete mix by volume, cement is responsible for nearly 90% of the material’s carbon emissions, largely due to the energy-intensive processes of extraction and heating.

In 2024, Taiwan produced just over 9.9 million metric tons of cement, down from an average of roughly 13.9 million metric tons during the 2010s and a peak of around 28 million in the 1990s, according to the Ministry of Economic Affairs. Although production has been declining, cement remains a significant domestic industry — one that continues to draw scrutiny for its environmental impact, particularly the degradation of landscapes caused by extraction and processing.

C-Cube’s Liou says both emissions and environmental damage can be addressed by developing “recipes” that replace concrete aggregate and carbon-intensive cement with locally sourced waste materials.

“The eventual idea is to use zero cement and concrete — and actually we have demonstrated that we can do that,” Liou says.

The key to C-Cube’s cement reduction strategy is “C-Slurry,” a 100% recycled construction material composed of steel slag, lime mud, sludge from wastewater treatment plants, and sawdust. This waste-based binder eliminates the need for the carbon-intensive limestone extraction and high-temperature heating required in conventional cement production. It also gives a second life to post-industrial waste that might otherwise pose environmental risks.

In its basic form, C-Slurry resembles traditional concrete in both appearance and texture. It has already been used to create sculptures, public furniture such as benches and chairs, and even desks in restaurants and offices across Taiwan. According to Liou, its performance is on par with conventional cement — a notable step forward in the science of alternative building materials.

Yet cement is only half the story.

“In our case, we use oyster shells from the Taiwan Sugar Corporation, which are processed at low temperatures to remove impurities — not calcined,” said C-Cube Project Manager Jensen Huang in an email. “This means their carbon footprint is much lower, and in our system, they are mainly used to replace sand or gravel as aggregate.”

Taiwan Sugar Corporation, or Taisugar, in 2021 opened a Tainan facility dedicated to the circular reuse of oyster shells. In partnership with the Industrial Technology Research Institute (ITRI), the company is transforming discarded shells into high-value biomass materials.

The process involves recovering and calcining the oyster shells to produce calcium carbonate or grinding them into fine powder. These materials are then repurposed for use in Taisugar’s own feed mills and farms, as well as supplied to domestic manufacturers as a locally sourced alternative to imported calcium carbonate used in animal feed and fertilizers.

Thanks to their chemical composition, oyster shells can serve as both binder and aggregate in construction materials. A study published in the scientific journal Nature found that adding up to 20% oyster shell powder to concrete mixtures can enhance the material’s strength, stress resistance, and water repellent properties.

Liou says C-Cube has already demonstrated the viability of its materials. The greater challenge, he says, lies in overcoming persistent skepticism within the construction industry toward recycled alternatives. “The construction industry is very conservative, so not many people dare to use new materials.”

Cost is another major challenge. Without industrial partners to scale the acquisition of raw ingredients and production, C-Cube’s products remain more expensive than conventional alternatives.

“As we scale up and collaborate with traditional building materials manufacturers, we remain open to discussions around blending — especially when navigating building codes or industry expectations,” Huang said by email. “In those cases, small amounts of cement may be introduced strategically, not because we can’t avoid it, but to ensure regulatory compliance and real-world adoption.”

Enter: Penghu’s oyster shells

In Penghu County, an archipelago 50 km west of Taiwan’s main island, one of C-Cube’s partners is finding its own way to shift perceptions about recycled materials. Circular engineering and design firm Coraal takes an aesthetic approach, weaving sustainability into local culture and identity to reframe how such materials are seen and used.

“Humans are visual animals, we like beautiful things,” says Coraal founder Born Hsiao. “Beauty affects our sense of value, and if your product isn’t beautiful, people won’t want it.”

Known for traditional coral-fragment architecture and a thriving seafood scene, Penghu faces a growing waste problem tied to its culinary culture. The county generates over 2,000 metric tons of oyster shell waste annually. With no local method of disposal, most of the waste is sent to mainland Taiwan. The process incurs shipping costs estimated at NT$4 million (approximately US$134,000) per year and generates additional transportation-related emissions. Shells that aren’t transported typically end up in piles along the shore, posing environmental and public health risks.

“I wondered if there wasn’t a way to solve the problem locally,” says Hsiao. “A way to use the waste to make something useful to the environment and to society.”

Together with C-Cube, Coraal developed a new material blend using oyster shells, which now forms the basis for a line of lifestyle products — including coral-shaped diffusers and lamps — as well as architectural features like decorative walls at public beaches, inspired by Penghu’s traditional building styles.

While Coraal’s operations are not yet large enough to process all 2,000 metric tons of oyster shell waste produced annually in Penghu, Liou says partnerships like this can serve as a blueprint for applying C-Cube’s technology to local contexts — adapting sustainable materials to meet regional needs and resources.

“C-Cube can train people locally,” he says. “They don’t need the scientific experiments or research. We can do this and share our data to help them develop their own materials. When we go to Penghu, we can use oyster shells or coral fragments. When we go to Hualien, we can use marble.”

The idea extends to a variety of environments. C-Cube’s material recipes can already incorporate brick and concrete waste from urban redevelopment, straw from agricultural regions, and marble scraps from eastern Taiwan, demonstrating the potential for region-specific solutions rooted in local waste streams.

Low carbon solutions

Around the globe, other companies are developing alternative technologies to address the carbon footprint of cement and concrete. In the United States, Brimstone has developed a process to produce cement from carbon-free calcium silicate rocks that are “highly abundant” and “found on the surface of every continent,” according to the company. Sweden’s Cemvision, like C-Cube, relies on industrial byproducts from mining and steel production to manufacture a recycled form of cement.

The WEF First Movers Coalition, a group of companies “leveraging their purchasing power to decarbonize the world’s heavy-emitting sectors,” recognizes the value of burgeoning technologies like C-Cube’s. The coalition notes that roughly half of the emissions reductions needed to reach net-zero by 2050 will depend on technologies not yet deployed at scale. That, it argues, suggests the barrier is less about innovation and more about widespread adoption.

Both Liou and Hsiao similarly point to decentralization as a key factor in the shift toward recycled materials.

“The model of using waste to replace cement is something that can be applied to other places,” says Hsiao. “But each place has different waste and different circumstances. When you run into a local problem, you work with local partners to find a solution.”