The Foundation of a Carbon Problem
Concrete is, quite literally, the foundation of the modern world. From sidewalks to skyscrapers, concrete has transformed civilization for the past 200 plus years of its usage. It is the second most consumed substance on the planet, second only to water, with approximately 30 billion tons being produced annually.
However, there does exist a dirty little secret with this ever-present material: concrete accounts for roughly eight percent of global carbon dioxide emissions—the largest individual portion attributable to any sector of the economy, even greater than the entire aviation industry.
As climate change continues to impact the world at large, and the construction industry faces increasing scrutiny and demand to lower their impacts on the environment, an acceleration of rethinking one of the earliest human-made products for a carbon-conscience future has begun.
Understanding the Carbon Footprint of Cement
The problem with concrete begins with its key binding ingredient: cement. Making a standard Portland cement involves superheating limestone and other ingredients in large-scale kilns at a blazing 1450 degrees Celsius. This process uses up large quantities of fossil fuels. However, the challenge of emissions is more than an energy problem. With the heating of limestone, a chemical process occurs that emits carbon dioxide directly from the stone itself – this is called calcination.
Approximately, 60% of the carbon footprint associated with cement production is from calcination, with the remaining 40% primarily from fuel combustion. Urbanization around the globe does not appear to be slowing down, and many emerging countries are at the outset of their infrastructure booms, so if global cement production continues on its current trend, it could increase 12-23% by 2050.
The Climate Stakes and the Construction Dilemma
The stakes could not be higher. Approximately 40% of the global energy-related carbon emissions lie in the construction and buildings sector, and production of those materials accounts for a sizable portion of those emissions. Achieving the climate goals of the Paris Agreement while at the same time building homes, hospitals, and infrastructure for a growing global population represents one of the greatest contradictions of the century. Instead of accepting this contradiction as one that cannot be resolved, innovators all over the world are approaching the challenge from various angles developing technologies and materials that could radically change the built environment.
Innovative Solutions Reshaping the Industry
- Reimagining Cement Chemistry
One positive path is to rethink the chemistry of cement itself. Various companies have been inventing new types of binders that may partially or completely replace Portland cement. Geopolymer concrete, in fact, uses fly ash or slag, both industrial waste products from either coal power plants or steel mills; to activate a chemical reaction using an alkaline solution.
Compared to Portland concrete, these geopolymers can reduce carbon emissions by up to 80%, and they usually perform better in strength and resistance to chemical substances. In Australia and Europe, geopolymer concrete has already seen commercial applications, from an airport runway to a residential home, showing that alternatives can be produced within the constraints of performance.
- Carbon Capture and Mineralization
Carbon capture technology is changing the narrative about concrete’s climate impact, helping to turn concrete from environmental villain into potential hero. Some fledgling companies are injecting captured carbon dioxide into concrete during mixing, where it mineralizes permanently in the structure of the concrete.
This process is called carbon curing, and it sequesters carbon dioxide that otherwise would be released into the atmosphere (from both the injected carbon dioxide and the concrete production process), and some even say carbon curing makes the concrete itself stronger.
A small number of companies claim their processes can help concrete be carbon neutral, or even carbon negative, thus transforming every building’s structure into a greenhouse gas vault. One company’s carbonate concrete has been piloted by several major ready-mix producers, and carbon cured concrete has been used in a small number of North American construction projects.
- The Circular Economy Approach
The circular economy is also changing the way concrete is produced. Researchers and companies are exploring techniques for recycling demolition concrete to make new building materials, which can help to both reduce virgin material use and ease the burden of large amounts of construction waste sent to landfills.
Recycled concrete aggregate could replace a large portion of natural aggregates in new concrete mixes, reducing emissions from landfilling and transportation. Researchers are developing ways to separate and reuse the cement paste from old concrete, recovering one of the most emissions-intensive components to give it a second life.
- Alternative Building Materials
Green alternatives extend beyond just concrete. Cross-laminated timber (CLT) and other mass timber products are starting to develop into legitimate alternatives for mid-rise construction in carbon-sequestering ways. Other bio-based products (bamboo, hempcrete, mycelium, and others) are becoming legitimate constituents of a supply chain and building codes, after having originally been noted as experimental curiosities.
These are appealing to the market as viable building materials not only because of their carbon credentials but also because of their aesthetic and performance characteristics that builders and architects favor.
Barriers to Widespread Adoption
Nevertheless transitioning is an effort faced by immense challenges. Construction codes around the world are inherently conservative in nature, having developed from many years of experience using traditional materials. Engineers and contractors will more often than not be hesitant to use a material whose performance or safety has not already been documented, and with good reason: buildings are designed to last decades, while withstanding earthquakes, fires, and severe weather.
The construction industry is inherently fragmented; too many small players with narrow margins creating inertia to adopt new ideas. Cost is also a factor and a barrier; while prices for green materials are continuously coming down, they will still usually come with a premium over traditional materials.
The Role of Policy and Industry Commitment
The pace of the transition is likely to be determined by government policy. If carbon pricing, building codes requiring emissions reductions, and public procurement policies that incentivize low-carbon materials accelerate adoption, implementation could happen quickly. The European Union has taken aggressive measures, with regulations that require emissions reporting for construction products and mandates that new construction achieve net-zero performance.
California and other progressive jurisdictions are enacting their own low-carbon concrete specifications. Green building certification systems, such as LEED and BREEAM, are adding embodied carbon requirements, which incentivizes developers to adopt lower emissions materials.Major cement companies recognize that climate change poses an existential threat to their business model and are committing to net-zero emissions by 2050.
Regardless of whether this stems from true commitment to the environment or fear of regulations and reputational damage, their corporate ethos matters. These corporate giants control both the capital, distribution channels, and the local technical competencies to rapidly adapt new technologies to scale. Their research facilities are working on new cement formulations, investing in carbon capture systems, and cooperating with startups to commercialize new innovative solutions.
Conclusion: Creating a Sustainable Future
The race to decarbonize concrete is not just a technical challenge, but a fundamental rethinking of how we build our world. This effort will take a collective push from materials scientists, engineers, architects, the political community, and investors, as well as the will of builders and the populace to heighten the pace of change. The solutions are either in place or happening quickly, but we need the political and social will to realize them at the speed and scale that climate calls for.
At this point in time, consider the irony: concrete, the foundation for the carbon-intense, modern world, may literally be our means of building our way out of the climate crisis. Every building built, every road paved, and every bridge built, is a choice to abandon or accept humanity’s past. The race is underway, with the finish line being a built environment that will continue to offer shelter to humanity without heating up the planet.
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