Concrete Jungles: 6 Cement Alternatives that can Reduce its Impact in Cities
The expression “a perfect storm” refers to an event (typically an unfortunate one) which is exacerbated due to a confluence of negative or unpredictable factors. It is widely used when describing meteorological phenomena, but can also be applied to other contexts, such as the economy. The analogy can also be used to describe the relationship between the climate crisis and the world’s dependence on concrete. As demonstrated in the Chatham House report, while cement (an essential element for concrete manufacturing) is extremely detrimental to the greenhouse effect and climate crisis –representing about 8% of global CO2 emissions–, its global production is nevertheless expected to increase over the next 30 years. It is said that this increase will stem from the demand for rapid urbanization in regions such as Southeast Asia and sub-Saharan Africa. At the same time, the last IPCC report warned that we only have 11 years to reduce emissions and prevent irreversible damage due to climate change. In other words, the cement industry is facing a significant expansion at a time when emissions need to fall rapidly – a perfect storm.
Each year, more than 4 billion tons of cement are produced. As shown in this article by The Guardian, “After water, concrete is the most widely used substance on Earth. If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8bn tonnes, surpassed only by China and the US.” However, emissions from the construction sector would need to be reduced by 16% in order to reach the goals of the Paris Agreement by 2030; while it is estimated that global cement production will increase to more than 5 billion tons by 2050.
Throughout the manufacturing process of cement, clinkerization accounts for over 50% of carbon emissions. Clinker, or Portland clinker, is made by burning ground-up raw materials (predominantly limestone, but also clay and iron oxides and aluminum) at temperatures as high as 1,450 °C. The ovens used are usually heated using non-renewable sources such as natural gas or other petroleum derivatives. It is estimated that for each ton of clinker produced, between 800 and 1,000 kg of CO2 are emitted, including what is generated through the decomposition of limestone and the burning of fossil fuels. As pointed out by The Guardian, there are also other less-known environmental impacts: concrete is a thirsty giant, guzzling almost a tenth of the global industrial water use; and the material increases the urban island effect, absorbing the sun’s thermal energy and reducing the quality of life and biodiversity of urban spaces.
However, humanity’s dependence on this material is enormous. Concrete is harmful, but has also brought numerous benefits to society as we know it. It is very rare to find a building that does not use any cement, either for its structure, finishes or floors. Most urban infrastructure also depends on concrete, as well as large structures such as bridges, roads, hydroelectric dams, etc. But unlike plastic –another great villain of our times–, it is much more difficult to change our use of concrete and cement. For example, we can say no to a plastic bag or disposable product, but we cannot forgo using water just because it comes from concrete pipes.
So we find ourselves in a complex dilemma: while there is a real dependence on the continued use of concrete, the effects of climate change can be increasingly felt in our everyday lives, as seen in this summer’s European heatwave. Although a variety of innovative materials have shown potential in reducing the industry’s carbon emissions, it is almost naive to believe that concrete can be replaced in the near future. Nevertheless, there are some options to make the production of concrete more eco-friendly, and to reduce its use in construction:
Ashcrete uses fly ash (a by-product of coal combustion) as a predominant raw material for concrete production. When mixed with borate, bottom ash, and a chlorine compound, it can create a stronger, more durable and environmentally friendly alternative to Portland cement. Compared to traditional concrete, Ashcrete is more resistant to acid, fire, drastic temperatures and corrosion. As a byproduct of coal combustion, fly ash cement is also much cheaper than regular cement. But for this same reason, it may not be economically viable to produce Ashcrete at a large scale, as the use of coal is meant to be reduced in the future, therefore limiting the supply of fly ash.
Through a method created by a company of the same name, Finite binds together the fine grains of desert sand to create a material that is as strong concrete and that can be easily melted and reused, or left to safely biodegrade. Like concrete, Finite can be molded into any shape or size, be coated natural pigments and doesn’t need to be burned as clay, meaning that it consumes less energy. However, a negative point to consider is that we have already used huge amounts of sand throughout the world, possibly making sand scarcity the next sustainability crisis, and therefore reducing the potential of Finite.
Hempcrete is a mixture of hemp fibers with lime and water. It creates bricks that are eight times lighter than concrete, but cannot be used for structural purposes, although it can be integrated within traditional building construction systems. Similar to traditional concrete, hempcrete can be molded on site or prefabricated into construction components such as blocks or panels. Hempcrite is moisture free, prevents mold and is unappealing to termites, making it an attractive option for internal use. Because it contains air pockets among its particles, the material has great thermo-acoustic insulation properties, making it ideal for additional isolation. It is important to remember that, despite the potential of hemp-based construction materials, this plant is still prohibited in many countries.
Mushrooms have the advantage of being materials that can grow under various temperature and moisture conditions. The research on this is still early, but there are examples of promising uses for non-structural applications. Italian company Mogu has developed a mycelium-based product line that includes acoustic sheets, floors and panels. This biomaterial is highly porous, providing great acoustic performance in terms of sound absorption, and benefitting air quality by absorbing toxins.
Discovered by mistake by researcher David Stone, Ferrock is created from steel powder – which is usually discarded from industrial processes – and silica from ground glass. The material hardens when exposed to high concentrations of carbon dioxide, which is absorbed and trapped, causing the compound to become carbon negative. The result is a material five times stronger than Portland cement. However, the challenge with this material is to make it more accessible at a larger scale, as it is composed of industrial by-products and can have limited production.
Graphene is a nanomaterial composed of carbon and the thinnest known crystal. It light, an electrical conductor, rigid and waterproof, and can be used as an additive to concrete, increasing its resistance and durability. As it allows thinner structures to be built, it could significantly reduce a building’s carbon footprint. Currently, access to graphene is an issue and, like many concrete alternatives, its uses and production are still in the early stages of development.
It is important to note that creating a product that can be used as widely and as often as concrete is not an easy task. In this sense, investments in innovation and research are essential.
This article is part of the ArchDaily Topics: Cities And Living Trends. Every month we explore a topic in-depth through articles, interviews, news, and projects. Learn more about our ArchDaily topics. As always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.