Modern Architecture's Dirty Secret: Concrete and the Climate

Modern architecture is one of those subjects that often divides opinion into one of two distinct camps: you either love it or hate it. 

But, the aesthetics of the building style aside, there might be a darker side to modern architecture that might just require us to rethink the way we build modern buildings — our overuse of concrete. As you are about to find out, concrete, from an environmental point of view, is a very bad choice of building material. 

Let's find out why.

How are modern buildings constructed?

Modern architecture, and specifically modernist architecture, is an architectural movement based on a number of construction technologies still in use today. Relying heavily on reinforced concrete, steel frame, and glass, the style aimed to promote a visual expression of structure and function, embrace minimalism, and reject austere ornamentation. 

The style came to prominence in the first half of the 20th century until roughly the 1980s when it gave way to postmodern architecture. Modernist buildings and their postmodern descendants have influenced and altered the look and feel of many of our cities and towns around the world. 

The availability of new strong materials, notably reinforced concrete, enabled architects and builders to erect tall buildings that were not possible up to that point. High-rise buildings and skyscrapers became the norm in many business districts, forever changing the skyline of many a city around the world. 

Love it or hate it, modernist and postmodern architecture has been something of a revolution, and one that is set to stay with us for some time to come. 

However, for those who cannot abide the austere, featureless, and often brutalist aesthetics of this style of building, it also has an Achilles heel that could, eventually, see a return to more traditional forms of building. It also turns out to be the style's greatest strength (literally and figuratively) — concrete.

First developed thousands of years ago by the Romans, concrete is one of the most widely used construction materials today. And for good reason. 

It is cost-effective to make and use, and has proved to be one of the strongest, most durable, and most resilient building materials ever developed. Surviving structures from ancient Rome, like the Pantheon, Colosseum, and a number of tombs are testament to its potential longevity. 

It is also incredibly versatile, has superb vibration and sound insulating properties, has relatively low maintenance overheads, and its raw materials are very abundant. To date, somewhere between 10 and 20 billion tonnes, give or take, of concrete is used every single year. 

And the problem is only set, pun not intended, to get worse. Over the next 40 years, or so, some experts project that the floor area of the world's buildings will double. If true, this would mean that the demand for concrete will only continue to grow. 

But why is concrete bad for the environment? Let's find out. 

Was modern architecture a mistake? 

We'll delve into the environmental impact of the modern use of concrete in a moment, but it might be worth exploring the societal impacts of the modernist building style too. Far too often the impact of things on human societies is overlooked when considering impacts on the environment, but this is a mistake. 

Human beings, our culture, health (including mental health), and societies are inextricably linked to the environment, including the built environment. In fact, this is often included as a core component of in-depth Environmental Impact Assessments. 

One key component of this is the impact of the built environment on mental health. There has long been something of a civil war among architects around the subject of what constitutes beauty in architectural styles. New styles are often criticized as "ugly" or "debased", although many (but not all) are later widely accepted. 

The reason for such disagreements is that beauty is by definition subjective, and thus difficult to quantify. However, a number of polls regarding modern architecture have found that it is not very popular with the people who use it, or have to look at it, every day. 

One poll, taken in 2020, showed that most people tend to prefer more traditional forms of architecture, such as classical and revivalist styles, to modern styles such as brutalism and modernism. The preferences cut across most demographic categories, indicating that the vast majority of Americans dislike modernist architecture.

Materials such a timber, stone/masonry, and brick are among the most popular. Buildings constructed from these materials are seen as "warmer", "friendlier", and generally more inviting to look at and use. Interestingly enough, this may not be just a matter of opinion — there might be something more tangible in it.

Various studies have shown that the buildings erected in our cities can affect our mood and general well-being. Such studies show an elevated level of mental health issues like schizophrenia, depression, and anxiety in urban dwellers. This may be a consequence of the distinctly different way of life in a city (and factors such as population density), but the aesthetics of buildings typically found in large cities may also play a role. 

If the results of such studies can be expanded to include the effects of architecture, then it can perhaps be argued that modern architecture may well be unhealthy.

This is, of course, hotly debated. 

Other studies have shown that the basic architecture of our brains might also play a part. Some specialized cells in our brain's hippocampus appear to be very sensitive to geometry and spatial arrangement. Perhaps our brains are also wired to prefer certain types of spatial arrangements.

Another factor is how modern architectural styles may have also severely damaged the way that people and communities interact, too. In the UK, the after-effects of World War II, namely "The Blitz", left a number of cities with substantial ruins. 

Many buildings, including traditional and historic buildings, were destroyed, leaving, in effect, a blank canvas in some areas for replacement buildings. Unfortunately, modern architectural styles were very popular among the most prominent architects of the time. 

This simultaneously serendipitous and unfortunate moment (depending on your point of view) led to many parts of the UK's cities being suddenly inundated with modern buildings. However, the movement also led to perfectly serviceable traditional domestic buildings being demolished in order to erect high-rise tower blocks to house the many people made homeless during the Blitz. This dramatic change in living style has since been shown to have negatively affected community and social cohesion in many major UK cities.

Of course, we'll let you be the judge and jury of this style of architecture. 

Is concrete bad for the environment? 

From a certain point of view, concrete might just be one of the most polluting anthropogenic materials going. It all comes down to carbon dioxide emissions. 

According to some estimates, if you were to isolate the concrete industry and make it a country, it would be the third-largest emitter of CO2 in the world. In 2015 alone, the entire industry emitted somewhere in the order of 2.8 billion tonnes of carbon dioxide. 

That is equivalent to about 8% of total emissions. With China contributing around 28% (2019) and the United States about 14% (2019), concrete has its fair share of "blame" for anthropogenic carbon dioxide emissions. 

What is more, concrete use is only set to continue to rise over the next few decades and beyond. Demand for cheap, quickly constructed buildings and infrastructure, especially in rapidly-growing countries like China and India, will only lead to more concrete being poured every single year. 

It is important to note that the main problem with concrete is the cement which is a key component of concrete. In case you are unaware, cement acts as the glue (binder) for the other main ingredients (sand, gravel, and water) that are typically used to make concrete. 

In the vast majority of cases, the cement of choice is a type called Portland cement. First invented in the early-1800s by a British engineer, today it is used in around 98% of concrete mixed and poured around the world. 

The production of this cement has been shown to release large amounts of carbon dioxide as a byproduct of the creation of a material called clinker. 

Clinker is a solid material produced as an intermediate product during the manufacture of one of the world's most common cement, Portland cement, and is one of its main constituents. The material is made by sintering limestone (fusing it together without melting it to the point of liquefaction) with aluminosilicate materials like clay in a cement kiln. Once made, clinker is then ground down and acts as a binder in many cement products. 

Today, cement kilns typically consist of a heated rotatable cylinder that heats the clay and limestone at around 1,400 degrees Celsius. This requires large amounts of energy and the process releases large amounts of carbon dioxide as a byproduct. 

Part of this process works via a chemical reaction called calcination. Here, carbon is removed from limestone, or calcium carbonate (CaCO₃), through combustion to produce calcium oxide, or quicklime (CaO), and carbon dioxide. The quicklime then reacts with other ingredients in the kiln to make the clinker.

It is this process that forms the lion's share (about half) of concrete's carbon dioxide emissions. Because this process is a basic chemical reaction, it is a very difficult task to reduce or eliminate CO2 creation through the use of different fuels or increasing efficiency. 

Around about 40%, give or take, of CO2 emissions from cement production are the result of the way that the kiln is actually heated. This is typically achieved using fossil fuels in order to raise temperatures enough to make the process work. The remaining emissions from the process are from the consumption of fuels to first mine the raw materials and then transport them. 

Concrete is used by pretty much every single country on the planet, but some are bigger consumers than others. By far the largest cement producer (and consumer) is China, quickly followed by India, and then the EU as a whole. The main driver for the rise in cement production and use in China has been the rapid urbanization of the country over the last few decades, with more people now living in high or low-rise concrete buildings. 

In India, the consumption of cement is set to increase dramatically as it speeds up the urbanization process. For the EU and the US, older kilns are still bad polluters, but there has been a significant investment in alternative fuels for powering cement kilns. 

But, CO2 is only part of the story. The production of cement also has other impacts on the environment. Heavy metal emissions are one of them. 

Depending on the origin and composition of the raw materials used to make the cement, the high-temperature treatment in kilns can release volatile heavy metals like thallium, cadmium, and mercury, to name but a few. Uncontrolled release of these toxic substances into the environment can be incredibly destructive. 

However, it is important to note that countries like the U.S., and U.K., and EU nations all have very strict environmental regulations to strictly control this. 

The cement itself can also retain some heavy metal impurities that cannot be completely removed during the calcination process. While these are usually well bonded within the cement material, and the concrete, there is a possibility that such materials can leach out of the cement over time. 

Another problem, as previously mentioned, is that the process of heating the kiln typically involves some sort of combustion. The use of fossil fuels for this process comes with obvious environmental impacts, but even alternative fuels are not without their downsides. 

Irrespective of whether fossil fuels or alternative fuels are used, the combustion process can, and usually will, release other environmentally dangerous emissions like nitrous oxides and sulfur oxides. Fine particulate matter, and other waste products from the combustion process also have their fair share of environmental impact too. 

In addition, a great deal of water is used in concrete production. Concrete is thought to suck up almost a 10th of the world’s industrial water use. And in some regions, such as Delhi, the dust from wind-blown stocks and mixers contributes a large amount of coarse particulate matter that forms part of the air pollution. Even the acquisition of sand used in the mix can be environmentally catastrophic — many of the world’s beaches and river courses have been destroyed by sand mining and the business is now often run by violent criminal gangs.

Taking all this into account, it is not looking good for cement. However, all is not lost. Something things can, and have, been done to limit the environmental impact of cement production. 

Should we return to more traditional forms of construction?

So far the case for concrete, from an environmental impact point of view, is not looking too rosy. But how do other building materials fair? 

What about bricks, for example? Bricks are generally made from clay (technically ground clay and water) that is either sundried or fired (essentially, baked), depending on the type. Traditionally, bricks were made by hand using molds, but more modern factories now automate the process using machines. 

Clay, like limestone for concrete/cement, is a very abundant substance on Earth, but the types used in bricks tend to have some very specific qualities. The source clay must be "plastic" so that it can easily be shaped (when mixed with water) and must be able to maintain its shape once dried and/or fired. 

Extraction of clay usually has a limited environmental impact and clay production often occurs pretty close to the source. 

The entire brickmaking process consumes a good deal of energy from mining, transportation, processing, and, of course, firing. Typically bricks go through a series of processes during their "firing" process that will include removal of water, oxidation, vitrification, and flashing or reduction firing. This all needs heat and quite a lot of it. 

Depending on the clay used, this process requires heat of between 400 degrees Fahrenheit (204 degrees Celsius) and 2,400 degrees Fahrenheit (1,315 degrees Celsius). 

However, there is a catch. Bricks need mortar to bind them together when buildings things. This, like concrete, tends to require cement (and by extension clinker). However, on a pro rata basis, bricks require much less cement than that seen in primarily concrete construction. 

One of the best aspects of using bricks is that they are incredibly durable buildings materials. Once made, they don't require much maintenance. In fact, some of the oldest bricks still in existence today are well over 3,500 years old, and still going strong. 

Another useful aspect to bricks is that they are completely recyclable. If buildings are carefully demolished, bricks can, and are, reused in other buildings (after a little cleaning). This is something that cannot realistically be said for concrete — i.e. you can only really crush it and use it as an aggregate. 

So far, hurray for bricks! But what about other types of construction, like say, timber or rubble/stone? 

Stone and timber (apart from brick) are some of the oldest buildings materials known to our species. While timber frame buildings have seen something of a revival over the last few decades, the use of stone has, more or less, given way to concrete. 

Timber buildings can be, theoretically at least, carbon-neutral and are widely considered one of the most environmentally-friendly building techniques around. As trees mature, they absorb less and less C02 from the air. So, if the mature trees are then harvested for use in buildings, and new young trees are planted in their place, the CO2 emissions from their use are limited. Timber also has some interesting physical properties that make it thermally efficient. 

Timber buildings are also relatively cheap and quick to assemble. Timber is also much lighter than concrete or brick, meaning it costs less to transport and work with. Since timber frame buildings are made from wood, their main components are non-toxic and do not break down into potential hazardous materials over time. 

Unlike other building materials, timber that reaches the end of its life is, obviously, biodegradable. In fact, wood, according to some studies, is considered the most environmentally-friendly building material of all. 

However, these buildings do suffer from being less fire-resistant than masonry or concrete buildings and require far more maintenance over their lifetime. 

Today, stone's use as a building material is normally the preserve of decorative features or facades, but it is another of the oldest building materials. Stone buildings are incredibly durable (they are stone after all), and are generally resilient to wind, fire, and water.

From an energy efficiency point of view, stone is an excellent material, as it has a very high thermal mass. This means it acts as an excellent insulator in temperate climates. 

If sourced locally, stone generally requires little travel and processing and is generally completely harmless (though this does depend on the rock chosen). Like timber and bricks, the stone is completely reusable at the end of its life. 

Ongoing maintenance costs are generally negligible, and the buildings are incredibly strong — think castles. 

So, what is the verdict? As we have seen, other building techniques are far more environmentally friendly than concrete.

But concrete has some inherent benefits that these more traditional forms of construction simply cannot compete with. After all, this is why concrete has become so ubiquitous.  

The main reason concrete has become such a popular building material is its inherent strength and versatility. You simply would not be able to build skyscrapers of the size and scale seen today with bricks or timber construction.  For reference, the tallest brick structure in the world is the Anaconda Smelter Stack, an industrial chimney built by the Anaconda Copper Mining Company near Anaconda, Montana, USA.

This building is 555 ft (169.2m) tall. The tallest concrete structure is Burj Khalifa, with a total height of 2,722 feet (829.6 meters). 

There are other benefits of concrete over other forms of construction, but we think you get the point. Since concrete is unlikely to disappear in the near future, is there anything that can be done to clean it up? 

Is there any way to reduce the environmental impact of concrete? 

As it turns out there is.

In fact, according to some studies, the overall emissions from concrete/cement production have fallen significantly over the last few decades. However, this has been offset by the enormous growth in concrete use over the same period — it has almost tripled since 1990. 

Such improvements have generally fallen into one of a few key areas. 

The first is the development of better, more efficient kilns. By requiring less energy to reach the necessary temperatures for the cement-making process, fewer emissions are released. The next is the increasing use of alternative fuels. 

Biomass or biowaste, as opposed to coal, is a common example. While encouraging, it is important to note that alternative fuels can have a significant impact on the environment in their own right. 

Thirdly, there has been a drive to reduce the amount of Portland clinker needed for the production of cement. Something called "high-blend" cement can reduce harmful emissions by as much as four times. Clinker can also be partially, or completely, replaced with other similar materials like waste products from coal plants of steel fabrication. 

Blast-furnace slag (a byproduct of iron and steel manufacturing) and pulverized fuel ash (a byproduct of coal power plants) have been used as partial substitutes for ordinary Portland cement for decades now, along with construction and demolition waste as a substitute for stone aggregates. All of these have lower embodied carbon than Portland cement.

Another interesting development is the field of so-called "innovative technologies" that effectively make use of carbon capture and storage systems. While not yet widely adopted, if at all, in the cement industry, some have predicted that it might become fairly common by around 2030. However, the technology is very much in its infancy and is still restrictively expensive to make viable for commercial applications. 

All very interesting, but there are other, more ambitious proposals for reducing the environmental impact of cement production. One example is the complete replacement for the need for Portland cement altogether. 

Most developments in this area are very much experimental, but if replacements prove to be as effective, and cheap, as Portland cement, there is little reason they shouldn't be able to rival it. For example, geopolymer-based cement has been under development since the 1970s. 

These products do away completely with calcium carbonate as the main ingredient and can harden at room temperature. Their only emissions are water. According to some companies working in this area, like Zeobond and banahUK, such products are able to reduce emissions by as much as 80-90%. 

Other companies are also working on something called "carbon-cured" cement using recycled aggregates and carbonation curing to permanently sequester CO2. These materials are actually able to absorb carbon dioxide, not water, as they cure. If such materials can be improved to absorb more carbon dioxide than they release during production, they could be a very interesting development in reducing concrete's impact on the environment. 

Some companies, like the US-based Solidia and the UK-based Novacem, are some notable examples. The latter, a spin-off from Imperial College London, has claimed that its magnesium-based cement is "carbon negative" and could act, theoretically, as a carbon sink — something of a gamechanger if ever realized at a large scale. 

Yet another interesting development comes from a North Carolina-based company called Biomason. They use bacteria to grow a bio-cement that can replace a proportion of the cement used in the building. The company claims its product is as strong as traditional masonry and, more importantly, acts as a form of carbon sequestration at the same time. One of their products, called Engineered Living Marine Cement (ELMc), while currently experimental, has self-healing properties. It is, however, mainly targeted for marine applications rather than those on land. 

All are very interesting, but there is one major problem with most of these innovations — they are largely untested, especially on a large scale. Portland cement has been in use for centuries and new alternatives have so far not been able to compete with Portland cement's understandable market position. 

One of the main reasons for this comes down to a very important consideration in any civil engineering or building project — safety. Most alternatives tend to also be tailored for specific uses, rather than a one-size-fits-all redirect replacement for Portland cement. 

Another barrier for new technologies is that quality and technical standards relating to concrete and cement tend to be based on Portland cement. Any upheaval in related industries that would come with authorizing the use of Portland cement alternatives would need new standards to be implemented and approved. This is not a quick process. 

That said, the industry is making some headway. Concrete mixes can now be specified which range from about 105 kg to 435 kg of CO2 per cubic meter, depending on the source of the raw materials, cement manufacturing methods, and the design mix.

In the absence of a viable replacement for cement, can anything else be done? Could we somehow reduce our reliance on cement and concrete? 

As it turns out we could, at least in theory. 

We've already touched on the potential for reverting to more traditional forms of construction, but there are other ways to reduce concrete/cement use. For example, urban designs can be reimagined to rely less on concrete. Cities can also be designed to rely more on walking than cars. Both of these could, in theory, reduce concrete use by around a third. 

Another option is to find ways to reuse concrete efficiently. For example, concrete waste from demolished buildings could be crushed and reused in new concrete-intense projects like roadworks. However, this will typically require new clinker to be added to ensure the structural integrity of the concrete. 

Of course, this kind of application could be a possible use for cement or clinker alternatives. 

Whatever the case, it seems unlikely that concrete and cement, as building materials, are going anywhere soon. While significant work has been done to reduce the carbon emissions from relevant industries, it is clear a lot more can probably be done. 

Unless that is, a return to more traditional and, in the eyes of many, more beautiful, buildings gain popularity once again. We can but hope.