The Burj Khalifa is an engineering marvel. Stretching 828 m into the Dubai sky, it is the tallest building the world has ever seen. Its construction used huge quantities of materials; 39,000 tonnes of steel*, 103,000 square metres of glass, and 330,000,000 litres of concrete (enough to fill 132 Olympic-sized swimming pools). From the top floor, though, one material dominates the view – sand, as far as the eye can see. So, you might be surprised to learn that the world is running out of this grainy material, mostly thanks to the concrete megastructures that we fill our modern cities with.
I’ve written about concrete before – either to discuss its carbon footprint, or the chemical processes that make it creep. So you probably already know that concrete has three basic components: cement, water and aggregate, combined in slightly different proportions. Cement is the powdery substance that reacts with water to form a ‘glue’. Because it’s made from limestone, and needs to be processed at incredibly high temperatures, the production of cement releases tonnes of CO2 per year. In fact, some estimates suggest that this single industry could be the cause of up to 8% of the world’s CO2 emissions. So far, so bad. But it’s concrete’s third ingredient – aggregate – that I want to talk about today.
Aggregate gives concrete its bulk. Depending on the mix, it can make up between 60 and 80% of the volume of concrete, and 70-85% of its weight. But its name obscures the material’s origins. Aggregate is actually made from a combination of course gravel and fine sediment, also known as sand. Again, the ratio varies a bit, depending on the strength requirements of the concrete, but sand can be up to 45% of aggregate. Concrete does require a specific type of sand, though.
Most natural sand is made by the very slow, continuous, natural process of weathering that occurs in lots of different environments**. You only have to look at satellite images of the Earth to see how plentiful desert sand is. Unfortunately, its wind-tumbled, rounded grains are too smooth and too small to be used in concrete. Instead, the construction sector looks to sand from quarries and riverbeds. Shaped by the water, its grains are much more angular than desert sand, providing the perfect rough, gritty surface for cement to stick to. As investigative journalist Vince Beiser says his book The World in a Grain, making concrete with desert sand is like “trying to build something out of a stack of marbles instead of a stack of little bricks.”
In recent years, the demand for sand has grown so dramatically, that suppliers have been looking elsewhere – namely, to beaches and the seafloor. The use of marine sand adds another step in the concrete-making process. Its salt must be removed, to avoid any risk of metal corrosion in the final structure. That comes with a cost, but the sand market is so crazy that apparently, it’s still worth it. Speaking to INSIDER in 2018,Beiser claimed that, because of its critical role in construction, “the price of sand has about quintupled in the past 30-40 years.” The makers of documentary film Sand Wars claim that sand is now a US$70 billion industry.
So what’s causing this growth in demand? The answer is rapid urbanisation, driven largely by China’s recent construction boom. In his book, Making the Modern World, historian Vaclav Smil shared a truly mind-blowing fact (which Bill Gates went on to feature on his blog). Between 2011 and 2013, China used more concrete than the US did in the entire20th century. I think that point is worth reiterating, because it astonished me when I first read it. In just three years, China consumed roughly one-and-a-halftimes as much concrete (6.6 gigatons) as the US used in 100 years (4.5 gigatons).And to make that much concrete, you need a lot of sand. Hence the current market.
China sources most of its sand domestically, and uses it to create bridges, roads, tunnels, and megatall buildings. Shanghai’s dramatic skyline was constructed almost entirely in the past 20 years. According to Beiser, the city has built more skyscrapers in that time “…than there are in all of New York City”. All of that relied on sand dredged from the main stem of the Yangtze River. When that was no longer an option, miners moved their activity to Lake Poyang, and now extract an estimated 236 million cubic metres of sand per year. That probably makes it the largest sand mine in the world.
China may be the biggest consumer of sand right now, but the issue is a global one. A UN report published earlier this year showed that sand extraction is far outstripping the rates at which it is replenished. According to a team of scientists who recently wrote about the topic in Science Magazine ($) and The Conversation, “Sand and gravel are now the most-extracted materials in the world” – measured by weight, they surpass fossil fuels and biomass. By every measure, our current level of sand use, particularly for concrete production, is totally unsustainable.
Sand finds many uses in cities. As well as being the main ingredient for glass, sand is also used to create artificial islands, like The Palm Jumeirah in Dubai. According to the UN, this single development consumed 186.5 million cubic meters of marine sand, and exhausted the region’s own reserves of the material. As a result, the sand used in the Burj Khalifa’s concrete skeleton was actually imported from Australia.
The island nation of Singapore also relies heavily on sand imports. Since becoming independent in 1965, its economic growth has been remarkable. But, by importing and dumping huge quantities of sand into the ocean, it’s grown geographically, too – by more than 20% in the last 40 years. The UN Environmental Programme says that “Having imported a reported 517 million tonnes of sand over the last 20years, Singapore is by far the largest importer of sand world-wide.” Until recently, Singapore sourced their sand (both legally and illegally) from their closest neighbours – Cambodia, Indonesia, Vietnam, and their main supplier, Malaysia. But in July, Reuters announced that Malaysia has banned all sea sand exports, including to Singapore, which, they say “could complicate the island-state’s ambitious expansion plans….”
In addition, you might also have seen various ‘beach nourishment’ projects, where popular tourist beaches are topped up with sand imported from elsewhere. These are growing in popularity, but as Andrew Cooper, a professor of coastal studies, explained to The Guardian last year, “Beach nourishment is like a sticking plaster. It does not remove the underlying reasons for erosion. Worse, it provides a false sense of security. In future, as sea levels rise, it will demand bigger and bigger volumes of sand to be effective.”
And in my opinion, this is where we see the real tragedy of concrete –the impact it has far from the bright city lights. Aurora Torres, one of the authors of the aforementioned Science paper, summed it up succinctly, when she said, “Our consumption of sand is outstripping our understanding of its environmental and social effects.”
For example, look at the damage that dredging can wreak on wildlife – unsurprising when you know that the process involves blasting powerful water jets at the seabed and riverbed, and sucking up everything that is released. This makes water cloudier, reducing precious light levels for corals and aquatic plants. It also damages and destroys spawning and feeding grounds for other species. China’s sand dredging activity in the Yangtze River contributed to the demise of the now-extinct Yangtze River dolphin.
Its social implications are profound, too. Increased erosion from sand mining makes coastal areas more susceptible to flooding, and may lead to the contamination of drinking water by sea salt. The ‘big business’ nature of sand extraction also makes it a magnet for crime. Take the Sand Mafia, a group of Indian criminals and businesspeople who runs the country’s black market. According to INSIDER, this illegal industry generates $US2.3 billion a year. At the heart of it are the thousands of impoverished workers who work in dangerous conditions to extract this precious sand. Many of them die or are left with debilitating injuries as a result.
Normally, I like to finish my articles with a positive final thought, but honestly, I can’t find one. Yes, there are lots of people out there looking for more sustainable ways to make concrete (including Solidia and Finite), but as yet, none can provide even close to the quantities industry needs. The global shortage of sand is not news to governments. In many regions, new restrictions on sand mining have been established, but they’re only partially effective. The reality is that our addiction to construction, and our growing population, are pointing to an ecological disaster in the making. It’s also one that’s largely hidden from us because, as Torres pointed out to The Guardian, “we don’t buy it as individuals.” If you take nothing else away from this article, let it be that cities do not exist in isolation from the natural world. The processes we use to build, and live in, them have profound implications beyond their borders. And if we want to reduce that impact before it’s too late, we need to use less. Of everything. Including sand.
* That number doesn’t include the 15,500 square metres of embossed stainless steel used in the building’s cladding.
** I’m not including the white sand of Hawaii that is actually made from the poo of parrotfish. Yes, really.
This story was originally published in August 2019. You can find it on Forbes: https://www.forbes.com/sites/lauriewinkless/2019/08/22/were-running-out-of-sand-and-cities-are-to-blame/