Low Carbon Concrete
Last week major construction firm Laing O’Rourke announced it would be replacing all concrete used in UK projects with low carbon concrete. It is believed the bid will reduce the company’s carbon emissions by 14.4 Million KG – a drop of 28 percent compared to 2022.* With building companies making this move we wanted to highlight exactly what low-carbon concrete is and how viable it is as a building alternative.
Concrete produces 7% of global greenhouse emissions with most of those emissions coming from the creation of cement. Cement is the main binder in concrete and is made through a process called calcination. Calcination is when limestone and clay, along with other materials, are heated in a kiln. This process is essential to cement making, however, extremely detrimental to the environment.
Concrete is such a popular building material because it is so versatile. For an eco-friendly alternative to be viable it needs to behave in the same way as regular concrete but release fewer carbon emissions into the atmosphere during its creation. To date there have been promising low-carbon concretes introduced to the market that have decarbonised the cement making process. This decarbonisation includes using alternative heat sources such as electricity instead of fossil fuels during the heating process. However, more excitingly, there has been the invention of Direct Air Carbon (DAC) capture plants that are designed to remove carbon emissions from the air. This carbon is then either stored or used.
Swiss firm Climeworks uses enormous fans to suck CO2 out of the air, burying it deep underground. US startup Heirloom uses limestone to capture CO2 while Canadian startup CarbonCure injects CO2 back into concrete. The CO2 in turn strengthens the concrete, reducing the amount of cement needed. It’s a win win situation. The World Economic Forum predicts these DAC capture plants will pull 300,000 tonnes of CO2 from the environment this year. With more DACs planned we can expect the removal of up to forty Million tonnes of CO2 a year by 2030.
Laing O’Rourke have already been using low carbon concrete in some projects but, up until now, have opted for products known as GBBS concrete and PFA Concrete. These concretes do not remove carbon during the calcination process, instead they remove cement altogether. Instead of using cement as a binder, GBBS uses Ground and Granulated Blast Furnace Slag as the main binder and PFA Concrete uses Pulverised Fly Ash. Ground and Granulated Blast Furnace Slag is a by-product left behind during the iron-making process while Pulverised Fly Ash is an industrial by-product left over from burning coal. This makes use of products that are otherwise a hazard.
As a building material low-carbon concrete is an excellent alternative to standard concrete. However, there are still cons associated with both forms of low-carbon concrete. GBBS and PFA concretes are only viable in the short term. As we become more environmentally friendly by-products such as GBBS and PFA will not be available. DAC capture plant concretes are much more viable overall however, the process of capturing carbon and then either storing or reusing is an expensive one. It is believed concretes created through DAC capture are up to 40% more expensive than standard concrete. This prices them out of the market for many. Of course, in time this will change, however, it may not yet be the most viable immediate solution for all.