This time of year, bushes of rhubarb, potatoes and lettuce can be harvested in abundance at The People’s Pantry, a community garden that doubles as a fresh food pantry in Blackpool, England. There are residents living in adjacent affordable housing units who tend to eat the fresh crops they grow. And along the ground beneath each raised soil bed is a smooth slab of concrete, strewn with pieces of ivory shell.
“They’re not that obvious at first … but as you walk on them, the shells become more visible as you go, and little flecks of white start to come out,” says Helen Jones, director of operations at LeftCoast, which runs the local community garden. She describes the concrete mix made with crushed shells that now serves as a flood guard for the garden, fortifying the space against stormwater runoff or heavy rain.
It wasn’t too long ago that frequent water inundations were a mainstay at The People’s Pantry. A regular day of rainfall will turn the garden’s corners into something like a quagmire, turning uneven ground into dangerously slippery paths, and even seeping through the housing into the land in between.
This led to Jones meeting with local officials last April to see how the issue could be fixed. Towards the end of the year, the garden’s visitors watched in amusement as a team of scientists at the University of Central Lancashire installed a promising solution: a permeable concrete mix made with cement, aggregate – materials such as gravel and rock that share are from typical concrete mixes – and discarded shellfish waste collected from nearby fish processors.
The material is the brainchild of Karl Williams, who leads the Center for Waste Management at the University of Central Lancashire. His focus on turning items that people traditionally consider waste into useful resources is what led him to start experimenting with using fishing industry shells that would otherwise be thrown into landfills to improve the built environment.
“We’re trying to reduce the carbon footprint of using waste materials, and we’re looking for local solutions,” Williams said.
When crushed, scallop and swell shells produce an ideal shape that increases the porosity of transparent concrete, a highly permeable form of concrete, which allows incoming water to drain right through the layer, instead of collecting on the surface as it would with traditional materials. In coastal, urban environments such as Blackpool, where flooding is more frequent due to climate changeand an abundance of hard surfaces and a lack of natural greenery means that there is far more runoff than can currently be absorbed, the shell concrete acts like a sponge, holding on to the water for a period of time before it seeps into the surrounding soil be released. – not unlike a sustainable urban drainage system.
For Williams, the appeal of using discarded shells to achieve this flood mitigation is that it also tackles the climate impacts of both food waste and traditional construction. The construction and use of our built environment is responsible for more than one third of global greenhouse gas emissions — the cement industry alone responsible about 8 percent of the planet’s carbon emissions – while food waste accounts for at least another 8 percent. The climate toll of both industries is what gave Williams the idea to develop the permeable concrete made from locally sourced shells as part of a European Union-funded multinational research project.
“There’s quite a lot of work in the construction sector looking at how you can use alternative materials,” Williams said, noting that the construction and food industries happen to be two sectors where “they don’t really talk to each other.” He describes the shell concrete, which he started developing in 2018, as “a channel for both industries to really think about the waste they produce, the products they produce, and how they can work together.”
Fishmongers usually remove the shells from coastal shellfish catches before selling them to retailers, producers or directly to consumers. By embedding them in the concrete material, it saves them from simply being thrown into landfills, Williams noted. There is also a cost-saving incentive for the fishmongers: Currently, in the United Kingdom, a shellfish processor wishing to dispose of waste shells in landfill must pay almost 100 pounds per metric tonso Williams says commercial operations have an incentive not to contribute to waste and instead give away their garbage to be reused.
Meanwhile, the more recycled material you can put into a building material like cement, the lower the carbon footprint of the production process. Replacing the aggregate with alternative materials can shrink the emissions typically generated by quarrying, processing and transportation.
So far, although the shells added to the concrete mix allow for improved porosity and compressive strength and reduce the amount of aggregate used by 20 percent by weight, Williams and his team haven’t quite figured out how to carbonize the overall material not. neutral. (Williams says the next phase of the project is to reduce the emissions footprint of the mix by exploring lower carbon cements and shell waste processing.)
In the research field, the idea of deploying crushed shells in aggregate solutions to mitigate flood risk is nothing new, nor is the use of ingredients otherwise destined for landfills in pervious concrete. A 2017 study tested the durability of pervious concrete using broken shells, while a 2020 conference paper experiment with crushed coconut shells in building materials, and a 2021 analysis investigated oyster shell aggregate for urban greening applications.
But it is one of the first to be used successfully outside of a laboratory. In addition to the Blackpool community garden, the shell concrete was laid in a historically flood-prone cycling route in the north of France, which Williams’ team worked with various organizations to implement. 2022. They are currently in talks to carry it out next at a third test site – a UK car park.
“I wouldn’t claim it’s the very first, or highly innovative, but it’s intriguing, right?” said Xianming Shi, a professor at the University of Miami who studies sustainable construction materials. Shi is not convinced that the crushed shell concrete is a large-scale answer to either food waste or emissions associated with concrete. He pointed out that although decomposition of food waste in landfills is a worrying source of emissions, shellfish does not contain as much organic waste as other food products, such as fish or vegetables.
He also argued that this material is unlikely to be a primary driver in reducing emissions from the cement industry, because using a recycled material to partially replace aggregate in concrete will not significantly reduce the life cycle footprint of the concrete , unless it is recycled material carbon negative.
Rather, Shi sees it as a way to get public engagement with these and other emerging techniques that could ultimately make more of a difference. “This type of project, maybe it leads to further interest in unconventional concrete,” he said. Other examples include a living microalgae used to produce bio-cementdeveloped by researchers at the University of Colorado Boulder, or the work of scientists from the National Renewable Energy Laboratory to create a lignin-based resin which replaces the cement in concrete.
Some of these may have wider applications than shell-based concrete, which, like other forms of concrete, was used absorb flood risk around the world is riddled with restrictions. For one, high-porosity concrete also tends to have lower compressive strength than traditional pavements, meaning it’s usually not strong enough to act as structural concrete for foundations, nor is it common in high-traffic areas. not used. Many permeable concrete mixes also require regular, specialized maintenance to prevent problems. But while the shell concrete may not work as a large-scale solution, Williams is looking at using it in low-load-bearing sites, such as gardens, car parks and pavements, where nearby sources of shell waste mean it is a better answer to flooding problems than other forms of porous concrete.
In a warming world, a sea shell concrete may just end up as one of many quick localized solutions in the building and construction industry’s adaptation toolkit.
Williams’ team are now mapping out where outside the UK the types of shellfish needed for their concrete can be found to better understand where else it can be tested. Each location presents its own engineering challenges, as different types of shells break differently, which matters for the porosity of their product. So what works for an urban garden in Blackpool, England, a coastal town not far from an abundant number of cockles and wulks, or a cycling route near French waters where scallops are not in short supply, may not work elsewhere not.
More than eight months have passed since The People’s Pantry installed the shell concrete, and Jones says this is their first growing season in years where they haven’t had to deal with a single flood. “There was no surface water at all,” Jones said. “I mean, we’ve had some pretty downpours, but you can walk right out and there’s nothing held back.”
And while Jones is enthralled with its multifunctional purpose of reducing the need for concrete aggregate as well as using food waste (she calls it “brilliant”), visitors to the community garden are often captivated by a much simpler concept: “The residents have a whale of a time to just pour water into it.”
