Concrete is the most widely used material in construction. Imagine that by the time you have finished reading this article, the global construction industry will have produced about eleven million litres more concrete. Shocking isn’t it? Second only to water, cement is the most widely used substance on the planet. It is therefore understandable how its benefits conceal enormous health risks for the environment. For example, all the plastic produced in the last 60 years amounts to about 8 billion tonnes. The cement industry produces this amount approximately every two years. In short, if the cement industry were a country, it would be the third largest emitter of carbon dioxide in the world.
Alternatives
Cement is a hydraulic binder in powder form. It is also called clinker. Combined with other materials of different sizes (such as sand and gravel) it gives rise to concrete.
Worldwide, approximately 80 per cent of buildings are made entirely of concrete. Nevertheless, there are alternatives to this material.
‘Straw and soil are for the poor. Concrete is modern!’ This is what was said to Alia, an architect in charge of constructing tourist buildings in a Saharan oasis. While observing the rows of trucks transporting the sand needed to produce the cement, over 1,200 kilometres, Alia wondered if something would go wrong.
A few years later, Alia Bengana still thought about that episode. She decided, together with her husband Claude Baechtold, to delve further into the nebulous world of cement. Into its ruthless and silent universe. Their extraordinary investigation gives pause for thought. Involving specialists, construction professionals and even ecological activists who question the real alternatives to cement.
Education
In a degree course in France, meantime, an architecture student will never forget when: ‘The professor announced that we would focus on cement constructions.’
She had read somewhere how this was a very resource-consuming material. And she wondered if it was still possible to have this kind of approach.
However, today many people, also in the field of education, express the wish to spread knowledge of more sustainable technologies. Along with that of more humble and equitable architecture. More ecological and less impactful even in the materials used to build them. Cement, as we have seen, is a special guardian. In other words: is all concrete inevitable? Are there alternative solutions?
Increasing durability
An environmentally friendly way to make a concrete building more ecological would be to increase its duration. What architects call durability. Ordinary concrete ‘physiologically’ cracks. Due to its volumetric instability over time. Under certain conditions, a self-repairing capacity would really represent a remarkable opportunity. That can be achieved by mixing, together with the usual concrete ingredients, substances that activate reactions capable of counteracting the degradation of the material. Materials which, when called upon, are capable of repairing the damage. Similar to the normal hydration process of concrete during casting.
Naturally, because concrete also has a life cycle. Which, although long, is not infinite. And it often manifests its ‘end of life’ abruptly and disastrously.
An impactful production chain
However, it has to be said that all this barely affects the impact of the production chain. Which is important, as we have seen. The ecological footprint of the concrete industry is considerable. It is responsible for around 5% of the total global CO2 emissions. Moreover, this only partly takes into account the environmental cost of transport and other related factors.
Some suggestions
Once a reinforced cement structure has been built, concrete begins to slowly absorb CO2 from the atmosphere. Through the process of carbonation.
Though this can be seen as a way to offset some of the initial CO2 emissions, carbonation also reduces the alkalinity of the concrete. Rendering the steel within the structure vulnerable to corrosion. And thus decreasing the strength. And consequently the durability of the structure.
So what are the alternatives to make concrete more environmentally friendly? Use construction waste materials in production. Identify products that require less thermal energy in processing. Improve strength and durability characteristics. Reduce CO2 emissions as much as possible.
For more: Béton. Enquête en sables mouvants
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