Concrete – the foundation of humankind #13
Our second most used substance on Earth after water
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At Survivaltech.club, our next topic is concrete.
Concrete is a crucial substance for our humankind as you will see. However, concrete (or more exactly cement, one of its ingredients) is a major emitter of CO2, accounting for 8% of all CO2 emissions!
This week, we’ll start by exploring why concrete is such an important topic and how it is made in the first place.
Next week, we’ll continue by learning in more detail about cement production. Most excitingly, we’ll have an interview with a founder of a low-carbon cement startup!
I’ve again learnt a ton over the last weeks and am excited to share the learnings with you. Let’s go!
Humankind’s love - concrete
Concrete is a true wonder material. It is durable and can take practically any shape directly also at the construction site. Furthermore, concrete is relatively cheap and widely available around the world.
Our humankind has undoubtedly recognized the unique beneficial properties of concrete.
Already Romans loved concrete and built their constructs with it. (See the cover photo from Pantheon, Rome)
Nowadays, concrete is the backbone for our buildings and critical infrastructures like bridges, dams, and roads. Water is the only substance that we use more than concrete on Earth.
Elhacham et al.’s (2020) graph below displays well the sheer volume of concrete on our planet Earth. Concrete accounts for approximately half of all human-made (= anthropogenic) mass.
As a general note, check how much our humankind has built on this planet. There’s currently as much human-made stuff as there is living biomass!
A logic tree of concrete’s ingredients
Now let’s turn into answering the following question: “What is concrete made of?”
Before we start, I want to present to you my newest diagram on Miro, where I’ve illustrated the ingredients of concrete.
The ingredients of concrete
Concrete is made by mixing up the following three ingredients:
1. Cement (Yes, concrete and cement are two different things!)
3. Aggregate (sand, gravel, crushed stones)
You can think that making concrete is like baking a cake. You must have the right ingredients in the right proportions to get the right outcome (here, durable and not delicious, though).
Watch this video by Practical Engineering on making concrete.
The roles of different ingredients
Cement acts as the binder in the concrete. It is the glue that holds the concrete together.
There’s typically only 10-15% of cement in the concrete mix.
The most widely used cement today is called Portland cement. Portland cement consists of the following main compounds:
These compounds are derived from limestone, clay, gypsum, and other cementitious materials.
However, it is worth mentioning that 80% of these compounds originate from limestone. This is a crucial piece of information regarding cement’s CO2 emissions, as you will later see.
Now you might ask why cement contains exactly these compounds?
Check out this amazing video by Professor Karen Scrivener from EPFL for the answer (Spoiler: it is related to the wide availability of limestone around the world).
Water is a crucial component in hardening the concrete.
When cement is mixed with water, a chemical reaction called hydration occurs. As a result, the compounds of cement (e.g. tricalcium silicate) dissolve in the water and form new compounds.
In addition, there forms hydrates inside the concrete. The volume of these hydrates is much larger, and so the hydrates will hold the remaining grains of cement and aggregates together.
Check out this fantastic and short(!) video by Professor Karen Scrivener on the hydration of cement. Absolutely fascinating.
Aggregate like sand and gravel, contribute to the strength of the final concrete and add volume to the concrete mix. Aggregates also cost relatively little and so drive down the cost of concrete.
The downsides of our love for concrete
While concrete is an amazing material, we use it in such huge amounts that also its negative impacts are colossal.
1. CO2 emissions: 8% of the world’s total CO2 emissions
Cement production accounts for 8% of the world’s carbon dioxide emissions! To put this into context, if the cement industry was a country, it would rank as the third most CO2 emitting country after China and the USA.
Next week, we’ll go through in more detail how exactly cement production makes these emissions and how we can tackle them.
2. Freshwater usage
The sheer scale of concrete production also puts a strain on the freshwater supply.
A study by Miller et al. (2018) estimates that concrete production was 9% of the industrial water usage in 2012.
By 2050, 75% of the water demand for concrete production is expected to occur in regions under freshwater shortages.
Pioneering startups in the concrete industry
The good news is that there’s a multitude of startups tackling the problems of concrete production.
Check out these fantastic startups that I discovered during my research!
CarbonCure: Curing concrete with CO2. USA.
Sublime Systems: Electrifying cement production (decomposition of limestone). USA.
Neustark: recycled concrete with CO2 enrichment. Switzerland.
Solidia: alternative cement mix with CO2 curing. USA
CarbiCrete: cement-free alternative from steel slag with CO2 curing. Canada.
Betolar: cement-free alternative from industrial waste streams. Finland.
Further learning sources
If you want to continue learning about the wonders of concrete and cement, I’ve collected here the best resources that I’ve found:
Lecture series on cement by École polytechnique fédérale de Lausanne on Youtube. Amazing free lectures on the science behind cement.
The report “Making Concrete Change: Innovation in Low-carbon Cement and Concrete” by Chatham House.
“Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World” - book by Mark Miodownik
Questions that I left wondering
What is the most sustainable construction material? With what should we build our civilization in the future?
Next week, we’ll go through in detail the process of cement production.
Most excitingly, we’ll hear first-hand a low-carbon cement startup founder how they are slashing the concrete industry’s CO2 footprint.
Amin, M. M., Jamaludin, S. B., Pa, F. C. & Chuen, K. K. (2008). Effects of Magnesium Sulfate Attack on Ordinary Portland. Portugaliae Electrochemica Acta. https://www.researchgate.net/publication/237335773_Effects_of_Magnesium_Sulfate_Attack_on_Ordinary_Portland_Cement_OPC_Mortars
Chatham House (2018). Making Concrete Change: Innovation in Low-carbon Cement and Concrete. https://www.chathamhouse.org/2018/06/making-concrete-change-innovation-low-carbon-cement-and-concrete
Elhacham, E., Ben-Uri, L., Grozovski, J. et al. (2020). Global human-made mass exceeds all living biomass. Nature, 588, 442–444. https://doi.org/10.1038/s41586-020-3010-5
EPFL (2018). Hydration 1: Overview. Cement Chemistry and Sustainable Cementitious Materials. Prof. Karen Schrivener. Youtube.
EPFL (2018). Introduction 1: Context. Cement Chemistry and Sustainable Cementitious Materials. Prof. Karen Schrivener. Youtube.
Miller, S.A., Horvath, A. & Monteiro, P.J.M. (2018) Impacts of booming concrete production on water resources worldwide. Nature Sustainability, 1, 69–76. https://doi.org/10.1038/s41893-017-0009-5
Practical Engineering. What is concrete? Youtube.
Watts, J. (2019). Concrete: the most destructive material on Earth. The Guardian. https://www.theguardian.com/cities/2019/feb/25/concrete-the-most-destructive-material-on-earth