New Ways to Reduce Embodied Carbon in Construction
Global efforts to reduce carbon emissions are well underway but need more impetus. Stepping up efforts to reduce the “embodied” carbon and energy maintenance costs in buildings and other construction activities offers renewed hope that the world can meet international net zero goals. The Intergovernmental Panel on Climate Change, or IPCC, recently released its AR6 Synthesis Report, which combines data from previous years’ reports on different aspects of climate change. The report’s overarching conclusion is that “human activities have unequivocally caused global warming of 1.1°C due to unsustainable energy use, land use, lifestyles, and consumption.”
And now even the net zero emission target to keep net temperature increase to below 2°C by 2050 looks more difficult than ever to reach, according to the GHG emissions future trends assessment in the IPCC Sixth Assessment Report. Thus, there is a race to control greenhouse gas emissions as fast as possible to try and avoid the worst effects of a climate catastrophe yet to come.
Total emissions for 2021 stood at almost 55 billion tons of CO2e (carbon dioxide equivalents), and atmospheric CO2 concentrations are higher than at any time in at least two million years. In 2020, buildings were responsible for almost 40% of global energy-related carbon emissions, comprised of around 28% from operational emissions (such as the energy needed to heat, cool, and power them), and the remaining 11% from materials and construction known as embodied carbon (Fig. 1).
Embodied and Operational Carbon in Buildings
Embodied carbon refers to the greenhouse gas emissions arising from the manufacturing, transportation, installation, maintenance, and disposal of building materials. Operational carbon refers to greenhouse gas emissions due to building energy consumption such as lighting, heating/cooling, and other operations. The embodied carbon can account for as much as half a building's lifetime environmental impact.
Every building comes with a large amount of embodied carbon. Raw materials, such as steel, concrete, aluminum, and insulation, are some of the major contributors to these emissions. Unlike the operational emissions, most embodied carbon is incurred upfront at the construction stage.
With housing requirements projected to double by 2060, thanks to increasing urbanization and population growth, there is a renewed call to find solutions to reduce embodied carbon.
Operational carbon is easy to measure from the energy consumed in buildings and forms part of the scope I and II GHG emissions. (Scope I emissions are from energy consumed that is generated in-situ, and scope II emissions are from energy consumed from external sources, for example power plants). In contrast, embodied carbon is both difficult to estimate and falls under scope III emissions (generated by sources that are not under the direct influence of the property owner). Therefore, the focus has been on reducing operational carbon emissions to meet the net zero targets. However, with housing requirements projected to double by 2060, thanks to increasing urbanization and population growth, there is a renewed call to find solutions to reduce embodied carbon.
Construction Methods and Carbon Footprint
Various construction methods have different carbon footprints. For example, timber (especially recycled or sourced from sustainably grown forests) has a lower carbon footprint than concrete or steel construction. The production processes of concrete and steel involve significant amounts of carbon emissions from the chemical reactions and high temperatures. While emissions per unit weight of concrete is much less than steel, the sheer quantity used (next only to water) makes it a source of significant emissions. On the other hand, some timber construction methods may result in clearing forests and harming ecosystems, which can increase the overall carbon footprint. Additionally, using recycled and low-carbon materials—such as recycled aggregates in concrete, fly ash (coal combustion residue from power plants), and ground granulated blast furnace slag (GGBFS) as cement replacement—and reducing construction waste can help lower the carbon footprint. It's essential to evaluate the entire lifecycle of a construction method to understand its carbon footprint fully.
It's essential to evaluate the entire lifecycle of a construction method to understand its carbon footprint fully.
Life Cycle Assessment (LCA) software tools, combined with large materials property databases that provide reliable embodied carbon figures, are now increasingly more sophisticated and readily available. Thus, it is easier now to calculate the embodied carbon of a building up front so that steps can be taken to minimize it.
Reduction In Embodied Carbon
There are several ways to reduce embodied carbon emissions in construction. Besides the ever-relevant principle of the 3Rs—Reduce, Recycle, and Reuse—innovative technologies to help reduce embodied carbon emissions are emerging. Some prominent examples are LC3 cement, which is made from calcined clay and lime; green hydrogen-based steel; 3D printing of buildings using sustainable materials; and incorporating carbon-capture technologies into concrete production.
Examples of Low-Carbon Footprint Construction
Several companies are pioneering low-carbon footprint construction and green building materials, and even deploying drones and AI to make inspection safe, efficient, and low cost, leading to better repair and maintenance. Here are a few examples:
Cement—JK Laxmi Cement, based in India, plans to achieve its net zero emissions target by 2047 using LC3 cement and other technologies. LC3 cement reduces the clinker factor in cement by 50% and the carbon footprint by 40%.
Clinker is a nodular material, the main ingredient in the production of cement, and produced by heating a mixture of primarily limestone (calcium carbonate) and clay (silica, alumina, and iron oxide), at very high temperatures, typically around 2642°F (1450°C). This process decomposes limestone into lime (calcium oxide) and forms various mineral compounds such as silicates, aluminates, and ferrites that give cement its binding properties. The production of clinker is very energy-
intensive and a significant source of carbon dioxide (CO2) emissions.
CarbonCure Technologies is a leader in low-carbon concrete production. This company uses technology to inject carbon dioxide captured from various industrial sources, such as a thermal power plant's chimney, into concrete to reduce its carbon footprint.
Green Steel—Many manufacturers worldwide are rushing to green hydrogen-based direct reduction of iron ore, followed by electric arc furnace steelmaking. Steel manufacturer Ovako has built a hydrogen facility at one of its steel mills in Sweden to produce low-carbon green steel.
Cross Laminated Timber (CLT)—is a low-carbon building material that is gaining popularity in construction. Several companies are pioneering the production of CLT, including Structurlam, SmartLam, and Katerra.
AI Inspection—Increasing the service life of built infrastructure by safe, efficient, and inexpensive automated inspection, leading to better maintenance and longer service life, is also an important strategy to bring down the whole-life embodied carbon footprint. Companies like RaSpect AI provide AI-powered drone inspection of infrastructure to provide such solutions.
Green Bricks—Bricks are an important construction product. Alternative bricks and blocks, such as pressed clay blocks, fly ash bricks, aerated concrete blocks, and those made from biomaterials like sugarcrete and hempcrete (see: “Building with Hemp Raises Climate Awareness” (theearthandi.org), could play an important role in reducing the carbon footprint of construction. Bricks and blocks made from renewable plant-based sources have a lower carbon footprint than traditional building materials like concrete and steel.
Beware the ‘Cobra Effect’
There is a lesson about unwanted policy consequences that may apply to construction reforms.
In late 19th century British India, there was once a cobra problem—in the capital city of Delhi, for instance, many people died from cobra bites.
The government responded with a scheme to reward any citizen who brought in a dead cobra. Naturally, people went after the killer snakes, and many were brought in dead.
It appeared the problem had been solved, as the number of snakebite deaths fell, but then something unexpected happened. As people ran out of snakes in the wild to catch and kill, they started breeding and killing snakes for rewards. Realizing this, the government stopped the rewards, and of course, people had no option but to let all the snakes loose! The “Cobra Effect,” or “perverse incentive” theory, is a perfect example of a well-meaning policy yielding unintended consequences.
Today’s policies pushing for efficiency and renewable energy have yielded good results in terms of new technology. But they have also helped increase consumption, creating more emissions rather than reducing them.
It's time to re-examine the carbon challenge afresh. For instance, instead of Reduce, Recycle, and Reuse, podcaster Seth Scott recommends adoption of Replace, Remove, and Recover as core principles.
Also, measuring efficiency isn’t enough to reach net zero emission goals. A far better approach is to replace the culprit, which is fossil fuel, and replace it with zero carbon alternatives.
*Dhanada K Mishra is a PhD in Civil Engineering from the University of Michigan and is currently based in Hong Kong. He writes on issues around the environment, sustainability, climate crisis, and built infrastructure.