Concrete: Taking on Construction Enemy Number 1?

Unless you have been living under a rock, or maybe a concrete slab, you will be well aware of the stunning statistics that relate to concrete within the construction industry.


As a species, we consume more than 4.1 billion tonnes of the stuff every year, more than any other material except water.[1]

It is also accountable for generating ‘2.8bn tonnes of CO2 every year,’ […] which equates to ‘somewhere between four and eight per cent of all global man-made carbon emissions.’[2]


As such, it is imperative that we look at ways of reducing the environmental impact of concrete. However, concrete is seen as irreplaceable due to a number of factors, all of which make it perfect for construction.


Concrete is:

  • incredibly versatile, as it can be moulded or used to provide a flat surface,

  • it is immensely strong and extremely durable,

  • can look good, and

  • is also readily available.[3]


So, what do we do?


Removing concrete use entirely is unlikely, and as such, we can investigate two key areas that may help reduce the future impact of concrete including:

  1. prolonging the life of existing concrete, or

  2. investing in concrete alternatives.


Prolonging the lifespan of concrete.

Professor Rebecca Lunn and her team at the University of Strathclyde, among other experts in the field of Ground Engineering, have been researching ways to prolong the lifespan of existing concrete structures that have been damaged.


These cracked structures, if in continued use, would need to be replaced, which is time consuming, expensive, and continues to increase carbon emissions.


However, using microbially induced calcium carbonate, Professor Lunn has found a way to repair and strengthen pre-existing concrete structures, negating the need for removal and re-laying.


Nicknamed ‘biogrout,’ this process can repair key architecture types that often result in demolition and rebuilding, including:

  • decaying Victorian infrastructures,

  • ageing post-war concrete infrastructure,

  • flood protection embankments, and

  • railway embankments.


Using urea fertiliser and a harmless S.pasteurii bacteria, a chemical process called urea hydrolysis occurs. Once a calcium source is then added a calcium carbonate biogrout is formed, caused by the formation of calcite carbonate crystals, which fill in the cracks and become a mineral vein in the concrete.



The calcite crystals, once formed, harden and join the two concrete structures back together.


This is similar to sticking a broken cake back together with buttercream icing.

A homemade cake on a marble kitchen countertop that has been glued back together with light coloured icing.

Picture a broken cake.[4]


You can stick it back together with buttercream icing, as you can see above.

The buttercream helps the separated halves of the cake join back together, creating a unified structure. However, unlike buttercream, when calcite crystals are used in concrete infrastructures, this chemical process creates a structure that is fully repaired and more importantly, strengthened.


By repairing and strengthening pre-existing concrete structures, we increase their lifespan and eliminate the need for rebuilding, which helps:

  • reduce construction waste,

  • reduce the amount of concrete produced for rebuilding, and

  • reduce embodied carbon emissions.


Global per capita consumption has nearly tripled in the past 40 years.[5]

A cracked concrete road.

Using concrete alternatives.

The demand for concrete[6] continues to rise, year-on-year and gives no indication of slowing down. As such, experts are considering concrete alternatives, which have a range of possible benefits for the planet.

  • They may utilise alternative products for production.

  • They may release less carbon than regular concrete in production.

  • Using CCS may remove the CO2 generated from concrete production, regardless of the method or ingredients used.


Two major players in waste recycling are making inroads into concrete production, products known as LC3 and CSA.


LC3, or limestone calcined clay cement, is clay that is blended with Portland cement. It has roughly the same properties as the more traditional material but some major benefits including,

  • A 40% smaller carbon footprint than that of traditional cement.

  • It can be made worldwide using impure clay, making it practical and economical.

  • Heating or calcining LC3 is only required at around 800 °C, significantly lower than the 1,450°C needed to produce ordinary cement. This limits the amount of CO2 needed to produce the cementitious material.

  • It does not use decomposing limestone, which releases more CO2.


“We have done full-scale trials in India and Cuba,” Scrivener says. In addition, an LC3 product was just commercialized in Colombia, she notes, and a full-scale calcining plant is being commissioned in Côte d’Ivoire.[7]

CSA, calcium sulfoaluminate, also draws a lot of attention for its friendliness to the environment.

  • CSA processing emits less than half the CO2 (less than 20% in some cases) because the level of limestone in the raw material mix is lower and the working temperature is 200 °C cooler.

  • The applications of CSA could be more limited as it hardens much faster than regular cement, but it makes it ideal for emergency repairs to roads and runways, for example.[8]

Concrete travelling from the delivery machine to a funnel at the other end, with a pair of arms and hands holding up the chute.

CCS

Another way to limit the carbon footprint of concrete production is using Carbon Capture and Storage.


In concrete production, the kiln needs to be heated to over 1,400°C which increases in carbon production, as often, fossil fuels are utilised to create this heat.


CO2 is also produced by the decomposing limestone, a key ingredient in traditional cement production.

CCS plants attached to cement kilns could capture the carbon that’s released and store it where it will not enter the atmosphere. This would remove the 60% of carbon emissions that come from production.


Therefore, the use of CCS, concrete alternatives, and cleaner fuels for cement kilns could result in concrete CO2 production being drastically limited in future, despite the continuing need for concrete.

A large concrete structure of many layers, with what looks like yellow handrails in between the concrete layers.

As our environmental awareness and technological know-how increases, the myriad of sustainable options, particularly for the construction industry, also continues to grow.


With widespread application across the industry, using the methods outlined above, we can reduce the impact of concrete production and usage, and continue to build structures that are prepared for use for the next 100-years.[9]


____________________________________________________________________________ [1] Wired.co.uk, ‘This concrete can eat carbon emissions,’ published 26.10.2021 by Oliver Franklin-Wallis, <https://www.wired.co.uk/article/concrete-carbon-capture-co2#:~:text=The%20cement%20industry%20alone%20generates,global%20man%2Dmade%20carbon%20emissions> [2] As above. [3] Building.co.uk, ‘What are we going to do about concrete?’ published 20.07.2021 by Thomas Lane, <https://www.building.co.uk/focus/what-are-we-going-to-do-about-concrete/5112516.article#:~:text=Concrete%20is%20incredibly%20versatile%20%E2%80%93%20it,widely%20used%20substance%20on%20earth> [4] Broken cake image from 2chickscakesandcatering blog, ‘Repairing a broken cake,’ published 28.06. 2009, <https://2chickscakesandcatering.wordpress.com/2009/06/28/repairing-a-broken-cake/> [5] Kimberly E. Curtis, civil engineer and concrete expert at the Georgia Institute of Technology, quoted in Cen.acs.org, ‘Alternative materials could shrink concrete’s giant carbon footprint,’ published by Mitch Jacoby, 22.11.2020, <https://cen.acs.org/materials/inorganic-chemistry/Alternative-materials-shrink-concretes-giant/98/i45> [6] Image from Pexels.com, courtesy of Markus Spiske [7] Karen Scrivener, research group leader at the Swiss Federal Institute of Technology, Lausanne (EPFL) quoted in above. [8] Image from Pexels.com, courtesy of Life of Pix. [9] Image from Pexels.com, courtesy of Pixabay

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