Researchers at the University of Córdoba have designed a paving block made from 100% recycled materials, turning seashell and mining waste into a durable, low-carbon alternative to traditional concrete. The innovation aims to reduce construction’s environmental footprint while advancing the circular economy.
The construction industry has a pollution problem. It is a major source of global carbon dioxide emissions and depends heavily on nonrenewable resources like sand and gravel. As demand for new buildings and infrastructure grows, so does the urgency to find cleaner, more sustainable materials.
Researchers at the University of Córdoba (UCO) in Spain say one answer could be underfoot — and underused. A team from UCO’s Belmez Higher Polytechnic School has designed a paving block made entirely from recycled materials, using mollusk shells and mining waste instead of traditional sand, gravel and cement.
Their goal was to show that a common construction product could be reimagined within a circular economy, where one industry’s trash becomes another’s raw material.
The project starts with an unlikely ingredient: the shells of Acanthocardia tuberculata, an edible saltwater clam known locally as corruco or langostillo and widely sold in canned form. These shells typically have no commercial value and end up as waste.
“The canning industry generates tons of this waste, which ultimately piles up in landfills,” lead author Ágata González Caro, a researcher in the Department of Inorganic Chemistry, said in a news release.
Instead of letting those shells accumulate, the team crushed them to produce a calcareous aggregate — a type of stony material that can take the place of sand and gravel in mortars and concrete. By doing so, they replaced one of the main natural components in conventional paving blocks with a recycled alternative.
But the researchers did not stop at the aggregate. They also set out to replace cement, one of the most carbon-intensive materials on the planet. Cement production involves heating limestone to very high temperatures, releasing large amounts of CO2 in the process. Cutting back on cement is considered a key step in decarbonizing construction.
To avoid using conventional cement, the UCO team turned to two other industrial byproducts: waste from a spoil heap at the Guadiato Valley mine and fly ash, a fine powder left over from burning coal. Both materials are often difficult to reuse at large scale and can pose environmental challenges if left in dumps.
The researchers mixed these wastes and subjected them to alkaline activation, a chemical process in which a highly alkaline solution triggers reactions that form new, cement-like compounds. In effect, they created a binder that can hold the crushed seashell aggregate together without relying on traditional cement.
The result is a pervious paving block — a type of block that allows water to pass through — made entirely from recycled components. According to the team, the blocks meet the mechanical strength, durability and safety requirements expected for this kind of material, despite containing no natural sand, gravel or cement.
By combining seashell waste, mining residues and fly ash, the work offers a practical example of how several polluting or hard-to-manage waste streams can be redirected into a single, useful product. It also aligns with broader efforts in engineering and materials science to develop low-carbon alternatives for roads, sidewalks and urban infrastructure.
The research team, which includes UCO scientists José Ramón Jiménez, José María Fernández Rodríguez and Antonio Manuel Merino Lechuga alongside González Caro, sees the paving block as both a technical and environmental milestone. It demonstrates that a fully recycled product can perform to standard while reducing pressure on quarries and cutting the carbon footprint associated with cement.
Still, the researchers emphasize that the work is not finished. They note that further studies are needed to improve aspects such as compaction and demolding — key steps in manufacturing that affect how easily the blocks can be produced at scale. They also plan to explore greener alkaline activators and other ways to reduce dependence on conventional chemicals in the activation process.
Beyond this specific product, the project highlights a growing shift in construction research. Instead of focusing only on stronger or cheaper materials, many engineers are now prioritizing environmental performance, asking how to design structures that use less energy, emit less carbon and make better use of waste.
If innovations like UCO’s recycled paving block can be scaled up, they could help cities build and renovate streets, plazas and parking areas with a much smaller environmental footprint. For coastal regions with active seafood industries and areas with legacy mining waste, the approach could also offer a way to manage local byproducts more responsibly.
The study, published in the journal Materials and Structures, adds to a small but expanding body of work on CO2-cured, alkali-activated paving systems. While more testing and optimization lie ahead, the concept points toward a future in which everyday infrastructure is built not from freshly quarried stone and high-emission cement, but from the leftovers of yesterday’s industries.
Source: University of Córdoba