HOW CONSTRUCTION CAN MAKE THE SWITCH TO LOW-CARBON CONCRETE PART 1

The headline statistic on concrete is stark, to say the least. The world’s most heavily used construction material is responsible for around 8% of the world’s carbon emissions. This is part 1 of a two-part article.

With this in mind, it is concerning that there is still no globally agreed standard for what constitutes low-carbon concrete. What is agreed is that, for every tonne of standard cement produced, a tonne of CO₂ is released. And cement alone is responsible for between 5% and 7% of total global carbon emissions.

Notwithstanding these emissions, that have traditionally been a by-product of concrete’s manufacturing process, there is no denying its literally monumental benefits.

Currently, there is no affordable, flexible and long-lasting material on the planet that can be used in construction to the extent concrete is used.

Unfortunately, the climate crisis demands more than utility; it demands sustainability. Here again, admirers of concrete have an argument: its thermal mass allows it to effectively absorb temperature variations, reducing energy consumption within buildings.

It also has a role to play in the circular economy, and we have seen an increasing number of projects demonstrating impressive materials recycling initiatives, as well as a growing use of industry by-products in concrete’s manufacture.

Circular economy

The Concrete Initiative is a European project led by a number of cement, concrete and aggregates associations. One of its roles is to highlight the benefits of concrete, from a societal, economic and sustainable perspective.

The organisation cites a number of exemplar case studies, including Switzerland’s Gotthard Base Tunnel, the world’s longest railway tunnel at a little more than 57km.

The tunnel itself has undeniable sustainability credentials, such as switching a huge amount of road traffic – both passenger and freight – to rail.

In constructing the tunnel, a total of more than 28 million tonnes of material had to be excavated. This resulted in another sustainability tick as all of the aggregates required for the tunnel’s concrete construction came directly from this excavated material.

Without question, we are seeing a shift, both from manufacturers and end users of concrete, towards more sustainable practices.

Talking points

The question of what can be done right now to reduce Concrete’s impact on emissions was recently put to experts at the World Economic Forum in Davos, during an event hosted by the global management consulting firm McKinsey & Company.

A number of levers to decarbonise concrete along its value chain were discussed:

• Reducing the amount of clinker in cement – clinker accounts for approximately 90% of the emissions released in cement production; the effect can be reduced by substituting, for example, fly ash, metal slag or calcined clay.
• Reducing the CO₂ from energy used in the production process – manufacturers are investigating alternative fuels and newer technologies such as kiln electrification, as well as developing proprietary waste-recycling businesses that target the use of industrial and municipal waste in their kilns.
• Storing or utilising remaining CO₂ emissions – at the Davos event, cement and concrete producers described how CO₂ can be stored in concrete aggregates when construction and demolition waste is recycled.

According to McKinsey, the industry is open to the development of a more circular attitude to cement and concrete. There is, the organisation said, an enthusiasm for ‘greening’ the process, bus also uncertainty regarding how best to invest in these value chains.

Catalysts of change

Yet, as the great diesel engine is now beginning to be challenged by more sustainable propulsion methods, such as battery-electric and hydrogen power, so the building material that has been with us since the neolithic age may finally have some sustainable competition.

Swiss-based materials manufacturer Holcim currently offers ECOPact, a broad range of low-carbon concretes, which promises to produce up to 90% less CO₂. The company is somewhat vague about the techniques and technologies it employs to achieve these numbers, and it has been reported that a significant amount comes from offsetting carbon, potentially through tree planting or forest conservation.