LIKE stars, snowflakes and blades of grass, sand is one of those things that seems to be in infinite supply. It has been a symbol for quantities beyond counting since ancient times. When the biblical hero Joseph faces an impending famine in the book of Genesis he “stored up grain in great abundance like the sand of the sea, until he stopped measuring it, for it was beyond measure”.
Fast forward a few thousand years and things have changed: we are running out of the stuff. “Sand is a lot like oil,” says of Michigan State University. “It takes a lot of time to make and it can’t be renewed.”
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That’s more than a little troubling, for sand is literally the foundation of modern civilisation. It is a crucial ingredient in concrete, bricks, plaster, glass and microchips. What’s more, efforts to mine ever more sand are damaging ecosystems around the world.
We can’t do without it, and yet now might be the time to stay our shovels. Increasingly, the world is waking up to the sand crisis and trying to tackle it. Learn to use less sand in a smarter way, and we might just stop this most precious of resources from slipping through our fingers forever.
Think of sand and you probably picture the golden-brown stuff on the beach, which is largely made of silicon dioxide. Yet sand is defined not by its composition, but by the size of its grains, which are smaller than gravel and larger than silt. Roughly speaking, that means between 2 and 0.06 millimetres. Within that range there is a huge variety – from the translucent pink stuff found on dunes in Utah to the black volcanic grains of some Hawaiian beaches.
The different kinds suit different applications, but there is one need that dwarfs all others. Between 60 and 75 per cent of the sand we mine goes to sate our hunger for concrete. It is tough, easy to work with and fairly cheap, which is why we use twice as much of it as all other building materials combined: about 30 billion tonnes per year. That is enough to build a wall 27 metres tall by 27 metres wide around the equator, says Pascal Peduzzi at the UN Environment Programme, who wrote a in 2014.
Concrete is made mostly of sand and its chunkier cousin gravel, with a little cement and some water mixed in. Most recipes call for large, rough sand grains that bind together well. So, although there may be mountains of the stuff blowing around in the Sahara, for example, those grains are no good for most types of concrete – they are too small and polished round by the wind. The best sources of concrete-compatible sand are river beds, beaches and the near-shore seabed. Sand from the ocean floor works too, although it needs to be laboriously purged of salt and chlorine.
Sand mining in such places can ravage the environment. For instance, in the past few years sand pirates have harvested so much grainy booty from islands in Indonesia that at least 24 of them have disappeared. Much of the sand is shipped to the cramped island state of Singapore, where it is used in land reclamation projects. Meanwhile, there are fears of ecological catastrophe in Indonesia.
There are many more stories like this (see “Aggregate armageddon”) and they show we have a serious sand problem. But it is hard to know exactly how serious. Few countries publish how much sand they extract, in part because widespread off-the-books mining means most don’t know themselves. It is telling that the official import and export statistics for sand don’t cancel out.
One workaround is to tot up how much concrete we use and then track backwards to calculate how much sand we must be using in construction. Alessio Miatto at Nagoya University in Japan used this strategy to estimate that in 2010 , plus another 11 billion of gravel.
Shifting Sands
The countries that import and export sand aren’t the ones you might expect, as these selected examples show
Our sand crisis is a classic case of the tragedy of the commons, where unfettered access to a common resource leads to demand that overwhelms the supply. One logical solution, then, is to set up and enforce rules on how much sand can be mined – but that is easier said than done, especially in remote places. “The real solution is to decrease our need for sand,” says Peduzzi.
In effect, that means reducing our use of concrete. Instead of building new apartment blocks, bridges, dams, car parks and more, we can repair those that are already standing. Concrete wear and tear often comes in the form of cracks that weaken structures and allow water to intrude and corrode the embedded metal reinforcements. In the US in particular, many structures are in dire need of repairs. In 2017, the American Association of Civil Engineers awarded their nation’s infrastructure , which means it is “at risk”. It found that every day there were 188 million trips across structurally deficient bridges in the country. The UK’s infrastructure received .
To fix the cracks researchers have turned to a surprising ally: bacteria. at the University of Delft in the Netherlands has developed a spray containing bacteria that produce calcium carbonate, which acts as a filler. In theory, concrete could also come with bacteria mixed in, which could spring into action and heal the building when exposed to the air. But the bacteria can’t fix cracks more than a millimetre wide. Moreover, many species can’t survive for long in concrete – a harsh environment that is about as alkaline as bleach, says of Binghamton University in New York state.
Oil well, heal thyself
Jin thinks she has a better idea: use fungi instead. They are tougher than bacteria and might provide a better healing additive for concrete. So over the past two years she and her colleagues have conducted the of whether fungal spores can survive in concrete and produce calcium carbonate filler. Screenings have shown up two strains that can pull it off. That isn’t a terrible batting average considering how hostile concrete is, says Jin.
However, a fungi-based concrete healing product is still years away. We can’t wait that long, says , a cement expert at the University of Aberdeen, UK. Take oil wells in the North Sea, he says. There are thousands of them out there, each of which needs to be plugged with concrete at the end of its life. That concrete can’t fail, or else residual oil would seep into the ocean. “The oil majors are desperately looking for solutions,” he says.
Imbabi is investigating new species of calcium carbonate-expelling bacteria, which he says offer advantages for oil wells because they can lie dormant for far longer than fungi. He is also looking at microcapsules that could be mixed into concrete. When ruptured they would release chemicals that react to produce a filler.
Still, even if self-healing concrete becomes a reality, structures will eventually become too badly cracked to repair. Once that happens, we can try a different strategy for reducing sand demand: concrete recycling. This already happens to some crumbling structures, which are cut into blocks and ground into aggregate that can be mixed into concrete in place of sand. The resulting material is even better than regular concrete for low-grade applications like road bases. But regulations prevent it being used in critical structures like bridges. Plus, there is .
So if we can’t repair concrete perfectly and we can only recycle so much, can we replace the sand with something else? The Romans made concrete with volcanic ash or a common mineral called pozzolan instead of sand, for example. More recently, we have tried out other options, from sawdust to sediment trapped by dams.
These generally involve trade-offs, however. Concrete made with sediment has only a fraction of the strength and durability of concrete made with virgin sand. The same goes for sawdust; you can only replace about a quarter of the sand in concrete before the material’s strength suffers.
Perhaps we need to go further and change the way we build entirely. Concrete structures typically have angular shapes with internal steel frames for support. That brutalist approach is hardly frugal in terms of material, but a new wave of architecture might change that.
Blocks by Block
The technology that underpins this change is 3D printing. Over the past few years, building firms have developed robots that can print concrete structures quickly and easily. Take San Francisco-based firm Apis Cor, which in 2017 printed the walls of a test house in Russia in 24 hours.
Printing concrete allows architects to experiment with innovative building shapes, some of which may use less concrete. But printed concrete is only suitable for certain structures at the moment, says , an environmental engineer at the University of California, Berkeley. That is because the boundaries between layers introduce weak points.
Concrete panels cast in a mould don’t have that problem, but they must be cleverly designed to save space and weight. This is the specialty of architectural researcher Institute of Technology in Zurich. His idea is to build structures from blocks that fit tightly together and support each other in compression. That means the concrete panels can be thinner – which in turn means less sand is needed.
The results can be striking. One example is the , a 15-metre-wide dome built from some 400 limestone blocks for the 2016 Venice Biennale arts exhibition (see photo). Block designed the structure so it would support itself without any adhesives.
“To consume less sand, we may need to entirely change the way we build”
It doesn’t have to be limestone, though. One of the group’s more recent projects is a new take on the most pedestrian part of a building, the floor. The consists of five interlocking pieces of concrete laced with an organic-looking pattern of internal ribbing. Again, the arched panels are designed so that compressive forces hold the floor up, like the ceiling of a cathedral, which eliminates the need for internal steel rods.
The result is only 2 centimetres thick and up to 6 metres across, and uses 70 per cent less concrete than a conventional floor. As a bonus, the space saving means there is plenty of room left over to fit heating and cooling pipes or wiring.
The Block floor is made using a 3D printing process that fuses together successive layers of fine powder to create a final form. This method is highly precise, but the printed materials are relatively weak.
A technique called , developed by the European construction firm Laing O’Rourke, could potentially solve that problem. FreeFAB uses a large robotic printer arm that spits out a specialised wax to make detailed moulds that are then used to cast concrete panels. It is a fast process and the material from the moulds can be reused. The method is already being used to produce concrete panels for the Crossrail project, a 100-kilometre railway line being built underneath London.
Switching to Block-style concrete building would lower our demand for sand, but lots of real-world iteration and testing must happen before we get to that stage. So perhaps in the meantime it is worth at least trying to firm up the rules on sand mining. A few international conventions touch on sand but they aren’t coherent, says Peduzzi. That is why Liu and his colleagues recently .
The first crucial step would be to find out how much sand there is and where it lies. Then we could start talking about where extraction can continue and at what level. In other words, we need a global sand budget. “So far research is scattered and fragmented – there’s no complete picture,” says Liu. Developing such a picture is something the international community needs to take seriously, Liu says, and soon. It is time to take our heads out of the sand before it disappears from around them.
Aggregate armageddon
Digging up sand and gravel is causing ecological damage around the globe
Coral blanket
Dredging sand from the sea floor stirs up a soup of particles. When the sediment settles, it blankets coral reefs and plants, stopping them feeding and photosynthesising. It can also clog marine animals’ gills, suffocating them.
Dolphin disruption
Dredging has eroded riverbanks on India’s Brahmaputra river. That has upset the ecosystem, threatening the Ganges river dolphin, one of the world’s most endangered freshwater mammals.
Marsh mash-up
Sand mining has degraded marshes in south-east Brazil that are important habitats for the critically endangered São Paulo marsh antwren, a species of bird that was only discovered a few years ago.
Tsunami magnification
The impact of the 2004 Indian Ocean tsunami , were it not for the removal of dunes that would have protected the coast. Upstream mining has also reduced the amount of sediment reaching the coast, meaning the dunes aren’t being replaced quickly.
Salted vegetables
At the Mekong river delta in Vietnam, sand mining has led to the intrusion of salty ocean water, which damages crops and affects the drinking water supply.
Cosy mosquitoes
Pools of water left behind by sand mining are the perfect breeding grounds for mosquitoes. In Iran, these pools are the most common habitats for the larva of the two species that carry malaria.
Aggressive clams
Boats used to transport sand may also carry invasive species like the Asian clam. Once introduced into a new area, these clams can outcompete other species and reduce biodiversity.
This article appeared in print under the headline “Sand storm”
