Cement & Concrete

Produced from limestone, cement is the largest manufactured product on Earth by mass. Combined with water, sand and aggregates it forms concrete, [the second most used substance in the world after water](https://www.theatlantic.com/technology/archive/2014/09/portland-cement-changed-the-way-the-world-looked/380140/#:~:text=The only thing that humans,of global carbon dioxide emissions.). Concrete is a trillion (!) Dollar industry of vital importance for our society's growth ambition.

How concrete is produced in cement plants (grey) and in concrete plants (blue). Source: own illustration

How concrete is produced in cement plants (grey) and in concrete plants (blue). Source: own illustration

Concrete has been all around us [since the Roman empire](https://www.history.com/news/the-secrets-of-ancient-roman-concrete#:~:text=They found that the Romans,were packed into wooden forms.&text=In addition to being more,be more sustainable to produce.). Yet, concrete is often thought of as a simple, ubiquitous grey mass. By no means this is the case: Concrete is a complex building material whose production involves multiple intricate steps at multiple sites.

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In a nutshell, one gets from limestone to concrete as follows. First, limestone is mined from an open pit in a quarry (1), crushed into pieces (2), and combined and homogenized with clay and iron ore (3). Next, at the cement plant, the limestone is ground in a so called raw mill into powder (4). The powder is pre-heated in a combustion chamber and fed into a rotary kiln to be calcined, i.e. burned at about 1400 degrees celsius (5).

This process gives cement its glue property but it is, at the same time, the most intense step in terms of carbon emissions. The resulting material is called clinker. Finally, the clinker is ground to very fine powder (7), now called cement.

Cement production runs almost 24/7 throughout the year. One of the biggest challenges is to guarantee stable quality at every step of the process at all times. This is difficult because limestone is a natural resource whose chemical and mineralogical composition varies from cubic meter to cubic meter even within the very same quarry. Moreover, for economic reasons cement is often mixed and diluted with other additives like slag, an industrial waste material from steel production, that introduce further fluctuations in quality.

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Leaving the gigantic plant cement is transported to multiple and much smaller concrete plants in the vicinity. Here cement, water, sand, and some additives are mixed on demand and dispatched to close-by construction sites.

Concrete plants face a similar challenge to guarantee stable quality like cement plants. In addition to changes in cement quality, concrete plants have to adjust to different moisture levels of sand and changes in weather conditions.

Why is concrete so practical? (In German)

Why is concrete so practical? (In German)

How is cement and concrete made? (In German)

How is cement and concrete made? (In German)

Where does alcemy come into play?

Studies have shown that green low-carbon concrete is possible - but until now it has been too complex and difficult to be produced reliably and at scale. It contains much less clinker than ordinary cement. The burnt limestone is replaced by filler minerals like limestone flour, for example. This makes low-carbon concrete vulnerable to fluctuations in raw materials and operating conditions and, thus, difficult to produce with reliable quality. Even worse: some properties of concrete can only be measured weeks after it has been poured on the construction site. It takes about 28 days for the concrete to fully harden. Of course, at this point in time it is far too late for any corrections in case something went wrong. This is why our world is still built with excessively robust, high-carbon concrete.

Using alcemy's software, cement and concrete producers receive precise quality predictions already during production. Based on these machine learning prediction models, our optimization algorithms identify which production parameters need to be adjusted to mitigate the impact of fluctuations. Consequently, the quality of cement and concrete can be optimized before delivery – for the first time in history. The result is significantly more consistent product quality, allowing producers to safely replace burnt limestone with less expensive, low-carbon materials found in nature.

What other approaches to reduce concrete's carbon footprint are there?

There exist lots of different proposed solutions for lowering the CO2 emissions of cement and concrete. Yet, these approaches often suffer from severe scalability problems.

We want to give you an overview about these strategies. This summary is mostly based on a great publication from the UN's environmental program (UN-EP), co-authored by one of our advisors Dr. Schneider. It can be found here and deems our approach to be a sensible solution:

There are very significant ecological returns from minimising clinker use in concrete. These can also be associated with a reduced unit cost on the assumption that Portland cement clinker is replaced by less expensive fillers. But such benefits can only accrue if the importance of good concrete mix design and quality control is understood by end users. [UN-EP]

Replacing cement by wood: The most obvious strategy — replacing concrete with other building materials like wood — is unfortunately not a viable option. In fact, the environmental effects of growing wood at scale, the chemicals necessary to treat it with, and the drastically shorter longevity do not necessarily make it an environmentally better alternative. In addition, for many applications in the infrastructure sector (think bridges, tunnels, etc.), there is no sensible alternative to concrete.

Any replacement for cement has to face the challenge of the sheer quantity needed, that is tens of billions of tons annually to build humankind's homes and infrastructure.

Carbon capture and storage or utilization (CCS/U) has the highest mitigation potential, but it is also by far the most expensive approach. It requires costly CO2 strippers in cement plants and a CO2 transport infrastructure. CCS needs CO2 to be stored in the ground, which is widely regarded as unacceptable in the EU. CCU at scale requires vast amounts of expensive hydrogen to be combined with the CO2. In fact, these requirements are so costly that “CCS/U is no longer necessarily the most promising technology for the reduction of CO2 emissions related to cement based materials", according to the UN-EP.