Concrete is a Sustainable Material !! 😈

Concrete is a Sustainable Material !! 😈

April 13, 2021

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There has been a lot of talk lately about sustainability in the construction industry and if concrete is not sustainable material and that wood should be used more. There is a misconception with concrete. People say its used because its cheap. That is not really the truth. The truth is there is no other option readily available for the structural requirements that are needed.

When you design a green building, the most important material chosen can be determined by weight or cost. Therefore, the predominant construction material, will usually come down to the structure of the building, which can be the most important factor for sustainable material There is little point in constructing a multi story tower, then using a small amount of sustainable timber cladding to cover the front of the building.

Completely eliminating the use of concrete is not an option, but can it be used in a way that is sustainable? The answer is yes, but it’s more complicated than you might think. So is concrete really that bad and is it a sustainable material?

Weight

You might be surprised to see below that research by (Hammond and Jones, 2008; Scrivener, 2014) proves concrete has a lower carbon footprint and lower embodied energy per kg in weight than wood, or steel or bricks.

The cement in concrete is the the main element that requires energy because of the heat required during production. Cement production is known for 5-8% of the global CO2 production. So why is concrete sustainable? Well, cement is only used in about 10-15% in concrete. This is quite small. When you put this in perspective and compare it with alternative materials, the above results above become more clear.

COST

A large cost benefit to concrete is the fact that its price remains relatively consistent. Availability also reflects the cost. However, the price alone is not the deciding factor, you have to take into factors below, which are only a few.

Self Heating
Disaster Resilience
Roads
Availability
Structure as finish
Passive cooling
Local construction cost
Fire resistant

All of the above can done within concrete construction. Therefore, minimizing cost.

WHAT ABOUT STEEL?

Steel does have its advantages in that the great thing about steel is that is about 100% recyclable. This recycling usage makes the material much cheaper when compared to other materials. Although the price of steel can fluctuate, it typically remains a less expensive option compared to reinforced concrete. Do not forget, that recycling also has a carbon footprint, through transportation. There are many countries where a steel structure is not readily available, which does not rank high in terms of sustainability. Steel frame structures can be the best option when taken into account cost, availability, sustainability, buildability, location and time on a project. It varies depending mostly on project location.

WHAT ABOUT WOOD?

The strength in a concrete column in a large building simply can not be replaced by a timber one. Recent mass timber buildings weigh approximately 1/5th of concrete buildings which is excellent. But do not ignore the fact that mass timber is not as strong as steel or reinforced concrete. Timber simply isn’t feasible to meet the building demands in cities. Plus, if you put it in the factor that 6% of world wood supply is from sustainable forests, implying that the remaining 74% contributes to deforestation. If the world shifted to more wood you can only imagine what would happen. We have to be careful that the new form of mass timber structures being produced does not encourage further deforestation. It seems, that mass timber will realistically be used in well developed countries and cities. Which is ironic because they are not really the places that need it the most.

SO WHAT IS THE BEST?

The question is not which one is better, because it depends on the project, location and size. If you look on any website, steel manufacturers will tell you steel is the best and concrete companies will tell you concrete is the best. What we can do to make things better is to combine different materials together within the structure to make it more sustainable. Wood does not have the strength of steel or concrete but it can be included within the reinforcement, for example. The most sustainable concrete is an all-natural mixture that includes a binding agent like hay, hemp, or rice straw, a mineral aggregate like sand, and an organic binder like animal blood or manure. These ingredients are often locally sourced and replenished. Disadvantage is this makes the concrete weaker. Getting the balance right for different projects is the trick. Combining more sustainable materials within the structure looks like the way to go. The future could lie in combining more sustainable materials within the structure, including concrete. We can then reduce the amount being used. So concrete is here to stay because actually concrete is a sustainable material. It maybe not the best material for construction. But it is by far means not the worse.

Russell M. Henderson (@ArchitectRussell) is a RIBA Chartered Architect working in Tanzania, East Africa. Russell also ‘edu-tains’ his passion for Architecture Travel & Film with video content on YouTube , TikTok & Instagram.