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Writer's pictureScience-by-Trianon
Sep 28, 20204 min read

Cement... A material of choice for sustainable buildings?

Updated: Apr 10, 2021

The production of cement requires vast amounts of energy and thus leads to the release of a significant amount of greenhouse gas such as CO2.

Limestone is the material of choice for the production of cement. However, its scarcity starts to become an issue.

The environmental challenges associated with CO2 emission, in addition to natural resources issues, will play a leading role in the sustainable development of the cement industry during this century.

Here we take a brief look at the environmental problems associated with cement production and possible solutions.





1. What is cement?


A cement is a binding element used in construction to hardens and bind other materials together.


It is commonly made of limestone, clay, shells, and silica sand, with limestone being the most used element.


Concrete is a complete building material used for foundation walls for example. It is composed among other things of cement, The addition of water activates the cement for binding the mix together to form a solid.


Cement and limestone are integral parts of the building world.


Buildings made from materials other than cement and limestone do exist but are very rare by comparison.




The annual global production of cement amounts to about 4 bn tonnes,[1] that of limestone is still some 280 million tonnes.[2]


The production of cement and limestone is a very energy-intensive process (the raw material is heated to temperatures > 1,400 °C in rotating kilns) and the industry is coming under increasing pressure to take action with respect to the UN's Sustainable Development Goals (SDGs).



UN's Sustainable Development Goals



The basic chemical reactions at the heart of cement production look like this: 
CaCO3 + heat gives CaO + CO2, which in contact with water (H2O) gives Ca(OH)2, which in contact with CO2 reverts back to CaCO3, losing H2O.




There are other uses for calcium oxide, e.g. in smelting, but by far the most important one is in cement making.


2. How does the building industry answer to the challenge of more sustainability?


As is always the case, there exists no one single solution that would solve the problem on its own. Instead, a variety of different solutions has to be researched, developed, and employed to achieve the aims and objectives.


In the case of the cement industry three major approaches are investigated:
1) Novel types of cement
2) Use of renewable energy in existing equipment
3) Novel building materials

2.1 Novel types of cement


This approach aims at reducing the amount of the so-called 'clinker' in cement.


Clinker is made a mixture of limestone and other minerals by heating it to sufficiently high temperatures so as to drive water out of it (typically around 1,400 °C).


On the addition of water, this material forms numerous cross-links giving it its hardness.


Obviously, heating large amounts of limestone to such temperatures requires vast amounts of energy.


It is estimated that the cement industry accounts for 8% of the global CO2 production.[3]
and
that the amount of clinker that could possibly be replaced by suitable filler material by the year 2050 is up to 40%, which in turn would save up to 0.2 gigatonnes of CO2.[1]


2.2 Use of renewable energy in existing infrastructures


Whether or not the amount of clinker could be reduced or not, substantial amounts of cement clinker would still be required, for which the kilns would still have to be fired.


One approach to reduce the impact of conventionally heated, i.e. fossil fuel-driven kilns could be the use of Carbon Capture and Utilisation (CCU).

The technology exists to capture the CO2 emitted by practically any combustion and to reduce the CO2 into hydrocarbons which could then be fed back into the combustion process. You can read our article about carbon capture and storage here [4] or our interview of Dr. Celia Sapart, an expert in C.C.U. here [5].


2.3 Novel building materials


A prime example of novel building materials would be cross-laminated timber (CLT).



Example of cross-laminated timber (Photo: Oregon Department of Forestry)


This material consists of wood panels that are glued together in opposite direction (with respect to heir grain) to provide strength.


It is lightweight, a good thermal insulator, and (since it is made of wood) sequestering carbon.


Surprisingly big buildings made from CLT have been erected [6], however, there are still restrictions embedded in local planning and building regulations.


In the US, the state of Washington has recently amended its building codes which have resulted in a series of buildings built from CLT.[7]



Conclusion: So is the cement material of choice for sustainable building?



As has been pointed out above, there is no single solution to global warming, not even to the subset of problems that is the cement industry.


However, things are moving in the right direction.


It is probably not just wishful thinking that, given a few incentives more from policymakers, this movement could gather significant momentum.


Our answer: For the time being... YES but for how much longer?

 

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