Are We Going to Run Out of Concrete?
In today’s climate-conscious world, it is increasingly common to wonder about the long term viability of anything that relies on natural resources, given how readily we gobble those resources up, and the growing demand for everything due to increasing population numbers. Concrete, being the second most in-demand substance in the world after water, is naturally one such point of concern.
Will we run out of concrete? Concrete is a material made of many ingredients, and the truth is we are well on course to be running out of sand with the next few decades in many parts of the world, and sand is a crucial ingredient in concrete. Sand can be manufactured, but not in a way that is as cost-effective as natural sand.
Concrete may be the second most in-demand substance in the world after water, but sand is the second most exploited natural resource after water, and it is starting to show. While concrete can be made without sand, it would be far less economically viable due to the ready-made nature and ease of accessibility that sand currently has.
Why is Sand Needed for Concrete?
If you are not familiar with the inner workings of concrete, it can help to think of it as a mix of glue and aggregate material. The cement—cement and concrete are two different things—is the glue that holds the aggregate together. It would be possible to use pure cement as a construction material, but it would not be economically feasible due to the fact that cement is so expensive compared to something like sand.
So what does sand do? In the concrete mix, sand—or other aggregates—acts as the strength component in the final mix, with cement holding it all together. The stronger the aggregate, the stronger the concrete. But it serves a far more economical purpose in that it significantly extends the use of cement. To understand how this works, consider a typical mix of concrete, which would likely contain the following proportions;
- One part cement
- Two parts sand
- Four parts other aggregates
A “part” is a scalable equal measure, meaning that in our concrete mix above, there is twice as much sand as there is cement, regardless of how much cement there is. So if you consider the same mix with cement only, you are looking at around seven times as much cement. By just taking sand out, you would be tripling the amount of cement needed for your concrete mix.
Now, granted, sand is just an aggregate, and other aggregates can be used. Rather than replacing those two parts of sand with more cement, they could just as feasibly be replaced with another two parts of aggregate. However, there is a problem with this plan when you consider that concrete—and in particular mortar—is often made without other aggregates in some cases.
Sand is used as an aggregate in concrete because it is uniquely suited to this role thanks to its availability, abundance, and the structural makeup of the individual grains of sand—specifically the shape of those grains. Sand—that is, the sand that is used for concrete—is angular and interlocks with each other to form a structurally sound concrete mix. This not only allows you to fill out your concrete mix with a far more inexpensive material than cement but that material actually adds to the structural integrity of the finished product.
Where do we Get Sand for Concrete From?
There are a number of different places where we can get suitable sand from for concrete, but the easiest, most affordable sand that is suitable for use in concrete mixing is found in riverbeds, something that is evident by the stark contrast that can be seen between images of the waterway connecting China’s Poyang Lake and the Yangtze River from 1995 to 2013. China has become the world’s largest consumer of concrete in recent years, and its demand is taking its toll on those natural areas that produce the right kind of sand.
You may be thinking that, if riverbed sand is perfect for concrete, why not seabed sand? Well, seabed sand is indeed suitable for concrete, and many-a-beach has been mined for its sand in recent years. However, it is not as simple as heading out with a bucket and spade.
With riverbed sand, you can float out into the middle of the river in a boat equipped with the right gear and essentially suck the riverbed sand up as though it were a milkshake. This is not feasible in the ocean for a few reasons, the first of which being that the ocean is a lot deeper than your average river, and the waters aren’t always so cooperative. But the larger concern lies with the organisms that live down there. The oceans of Earth were the starting point for life on this planet, and, to some degree, they are still a foundational element of continuing life.
The organisms that live in and around the seabed—organisms that would be severely impacted by the hoovering up of seabed sand—form the base of a food chain that, through various twists and turns, stretches all the way up to us humans. In short, scooping sand up off of the seabed would have consequences far beyond just depleting the sand reserves.
The next most obvious place to consider is the many deserts that stretch across the landlocked regions of our continents. Sand can be found in abundance here, and there is relatively little life compared to the ocean seabeds, so why not use that?
You may recall above that we mentioned the shape of sand being one of the reasons it is so useful as an aggregate for concrete. The angular nature of riverbed sand causes it to interlock nicely, which forms a much stronger concrete. Unfortunately, desert sand lacks this crucial feature.
Desert sand, thanks to the thousands of years it has spent being blown around in the dry deserts, has essentially been rubbed smooth by air friction, completely removing those angular features that are so useful. Desert sand would not be entirely useless as an aggregate, but it would not be able to serve as an adequate substitute for riverbed sand.
The best solution we have presently is manufactured sand, which, as the name suggests, is machine-made sand. The primary disadvantage to manufactured sand is the cost—manufactured sand cannot beat the price of the sand that is already there and waiting. That being said, this is mostly where the disadvantages end.
Due to the sand being manufactured, it is possible to ensure that the grains have the optimal shape for use in concrete mixing. It is also possible to ensure that there are no impurities in the sand and that the sand is made from a suitably strong material—granite is often the mineral of choice. Being free of impurities is a particular boon, as the organic compounds often found in natural sand can have adverse effects on the chemical reactions that take place within curing concrete, slowing the curing process down. And, speaking of organics, we don’t need to worry about hoovering up an entire micro-ecosystem worth of organisms with manufactured sand.
Concrete has been the most used construction material by humans for a long time now, and as durable and long-lasting as it is, we still need to tear our buildings down from time to time. This can be because the building is not safe anymore due to aging materials, or simply because we want to build something new. Whatever the reason, we often find ourselves tearing down large concrete structures, which tends to leave us with a lot of broken, aged concrete to deal with.
While it is not practical to break old concrete up to the point where it could be used as a substitute for sand in new concrete, it is possible to break it up to the point where it can be used as an additional, larger aggregate alongside sand. Concrete doesn’t have the best record when it comes to environmental friendliness, so anytime we can put old concrete to good use, we should take that chance.
This one is a little out there, but the concept of asteroid mining has become increasingly popular in recent years, in no small part due to Elon Musk’s SpaceX and its successes with pioneering space flight technology. It may not be a common suggestion, but it is not unheard of for the idea of extra-terrestrial resources to be put forth in any conversation about depleted natural resources here on Earth.
The reality is it is very likely that asteroids would have plenty of a suitable aggregate in the form of regolith. Indeed, due to the fact that regolith—think of it as “space sand”—has not been exposed to thousands of years of air resistance or water erosion, it will likely be extremely jagged in shape, which may even make it more suitable as a concrete aggregate than sand is.
Unfortunately, the reality is that it is not economically viable to bring something as mundane as asteroid regolith back to Earth in any significant quantities. The cost of getting into space is so high that anything coming back would have to be valuable.
Another way to consider it is; manufactured sand may be more expensive than riverbed sand, but it is not “launch a rocket into space” expensive!
When Will We Run Out of Sand?
There are no firm estimates for when we will run out sand if things continue at their current rate, and most of the estimates we do have are regional. For example, it is estimated that Vietnam could run out of sand within the next few years, whereas the average guess for the rest of the world is closer to the year 2050.
Further complicating the issue is importation. For example, Dubai imports a lot of sand from Australia. This also serves to illustrate the above point about desert sand not being suitable for use in concrete. Dubai features some of the most impressive buildings in the world, but despite being surrounded by endless stretches of sand, they import sand from other parts of the world.
Why Are We Using So Much Concrete?
The answer to this question is far more complex than we will be able to do justice to here, but in short; people. The population of our species has grown exponentially to the point where we are expected to have reached around nine billion living human beings within the next two decades. Compounding this problem of overpopulation is the fact that most of the people are or will be city-dwellers, which means an increasing demand for those concrete structures.
It’s worth noting that, even if those additional people did not want to become city-dwellers, they will be somewhat limited in options. Nature is critical to our survival as a species, and it has been fighting something of a losing battle against human expansion since we learned to chop trees down. However, as the population continues to grow, those areas of nature are going to become increasingly important, for their oxygen, for the food they grow, and even for their natural beauty, which will be increasingly coveted as city-life becomes ever more the norm.
The idea of running out of any natural resource—particularly one as seemingly abundant as sand—is understandably a scary thought. Unfortunately, it’s one we are going to have to confront in the coming decades. For many people reading this post, it is entirely possible you will be alive to witness a time when are out of practical sources of natural sand to use in construction.
That being said, construction will not just stop once we have depleted our natural sources of sand—we will not just run out of concrete. Manufactured sand, though more expensive, is a perfectly viable replacement, and right now, the only tangible downside to using manufactured sand is that the cost of construction may go up.
Still, a slightly more expensive home is better than no home at all.
And, of course, using manufactured sand allows us to get the construction materials we need without damaging the food chain by hoovering up the sea bed!