Carbon sequestration in cement enhances concrete construction

by sadia_badhon | October 2, 2020 8:24 am

By Nancy Novak

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When the topic of buildings and carbon emissions come up, most people think of climate control, minimizing power usage, and sourcing renewable electricity—all of these are important ways to do better by the environment. Operations are the major source of sustained, long-term emissions, and the primary focus of Canada’s Climate Action Plan as it relates to the commercial building sector. However, there is an opportunity to improve the environmental impact of buildings from the ground up.

Buildings are the third largest source of greenhouse gas (GHG) emissions in the country, followed by the oil and gas and transportation sectors. They account for approximately one-third of the country’s GHG emissions[2]. Across the globe, buildings and construction are responsible for 39 per cent of all carbon emissions. Eleven per cent of that is upfront carbon associated with construction, or embodied emissions.

Cement, the key component of concrete and the foundation of all formidable structures, is the primary source of embodied emissions. Cement generates around seven per cent of global carbon emissions. Every year, manufacturing cement emits more than two billion tons of carbon dioxide (CO₂) in the process of firing massive kilns, which require large amounts of energy and produce high volumes of CO₂.

For years, the construction industry has focused on operational opportunities to reduce the carbon impact of commercial buildings. Strides have been made to reduce volatile organic compounds (VOCs), creating safer environments for workers and occupants. There is a heightened awareness of transportation-related impacts on the environment and efforts have been made to source materials closer to the site. These are all important steps to protect the environment.

From a construction standpoint though, solutions to reduce the carbon intensity of new builds have been limited. Recycled steel and concrete fillers have driven some reduction in embodied carbon in new construction, but not made meaningful impacts.

Carbon sequestration technology

There is a real and effective opportunity to offset the negative environmental impacts of cement production with new technology that makes it possible to sequester carbon in cement. The technology focuses on converting CO₂ into a mineral and uses CO₂ in concrete to help manufacturers respond to the demand for green building products.

Using such technology, concrete producers mineralize carbon waste and inject it into concrete. The CO₂ is sourced from industrial emitters. They collect, purify, and distribute the CO₂ to concrete plants, which store it in pressurized tanks until it is ready to use.

Once injected into the wet concrete mix, the CO₂ reacts with calcium ions from cement to form a nano-sized mineral, calcium carbonate, which then becomes embedded in the concrete. This makes the concrete stronger. Aside from increased strength, CO₂ does not impact the concrete properties. Set-time, slump, workability, pumpability, air content, temperature, and finishing are unaffected; neither are hardened properties, including pH, freeze-thaw, density, colour, texture, and durability.

In addition to improving compression strength, mineralized CO₂ reduces the volume of cement used in concrete. Most importantly, it permanently eliminates CO₂ from the atmosphere, offsetting negative impacts of cement production on the environment.

For a measure of environmental impact by application…

• ready mix saves 11 kg (25 lb) of CO₂ per cubic yard;
• precast saves 11 to 18 kg (40 lb) of CO₂ per cubic yard; and
• masonry saves 0.5 kg (1 lb) of CO₂ sequestered per 30 standard blocks.

Solution applied

Compass Datacenters, a data centre construction company, recently learned of the carbon sequestration technology and committed to using it in the production of concrete for its new data centres, which rely heavily on concrete.

The number of data centres[3] worldwide has grown from 500,000 in 2012 to more than eight million today. Expansion is likely to continue on that trajectory as more people work, learn, shop, and stream entertainment from home in the wake of COVID-19. A lot of that expansion will be new construction in key markets, such as Toronto, Montréal, and Vancouver.

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Like other commercial buildings, most of the efforts of data centre operators, with respect to reducing carbon output, have been centred on less energy-intensive operations—servers and cooling systems with lower power requirements and/or sourcing renewable energy to reduce the carbon intensity of operations.

Given the extensive use of concrete in building data centres, from foundations and sidewalks to precast walls and roofing, carbon capture in concrete represents a huge mitigation opportunity. In its quest to build better buildings, Compass Datacenters set out to conduct due diligence on manufactured concrete using carbon sequestration technology and the impact it could have on Compass facilities.

Carbon sequestration technology potential

International engineering firm Thornton Tomasetti conducted a multi-year study on embodied carbon. In it, Tomasetti recognizes data centres and hospitals and mission critical structures, have the overall highest levels of embodied carbon of any asset category. In consultation with Thornton Tomasetti, Compass discovered the effectiveness of carbon sequestration technology in reducing the carbon footprint of each of its new campuses. Building sizes vary, but estimates showed using carbon sequestration technology has the potential to reduce the CO₂ footprint of each Compass campus by around 1800 tons, equivalent to CO₂ sequestered by 850 ha (2100 acre) of forest or driving a car for 64 km (4 million mi).

Having quantified the potential of carbon sequestration technology as it relates to Compass Datacenter projects, and with tested confidence in the integrity and application of the tech for Compass’s model, the next step was to revisit Compass’s supply chain to ensure a healthy network of precast providers who could deliver manufactured cement using carbon sequestration technology. With data centres under construction throughout the United States and a growing international presence, Compass needed assurance there would be a sufficient network of suppliers. It turned out the carbon sequestration technology manufacturers had more coverage than any other carbon-friendly products.

Compass sent a request for proposal to each of its existing precast providers with design specifications to gauge their readiness to work with the carbon sequestration technology. Several respondents were engaged, familiar with the product, and eager to support this new, better way to build. Ongoing partnership is important to Compass’s model and value to customers. Compass relies on partners who can support Compass’s strategic advantage with quality and speed-to-market.

Going forward

Canada updates building codes every five years and the next update is due to be published by the end of this year. According to reports, climate change will be a major area of focus in this and future editions. At the same time, local and state governments are beginning to adopt policies that suggest or, in some cases require, new construction to feature carbon sequestration in cement. All signs point to a mounting trend.

To help engineers and construction companies transition into a future with careful carbon measurements and proactive efforts to reduce carbon outputs, Thornton Tomasetti created a free embodied carbon measurement tool. It makes it possible to measure carbon in the design phase and helps identify solutions to combat negative impacts of new construction on the environment. It helps engineers measure embodied carbon in projects and find ways to optimize and reduce carbon output.

Compass is thrilled to begin constructing new centers with manufactured concrete using carbon sequestration technology this year and is continuing to seek out additional opportunities to deliver more carbon-neutral new builds, like using aggregate with captured CO₂ in place of natural limestone rock mined from quarries.

The decision to build new centres with carbon capture in the equipment pads and precast structures has been met with rave reviews from customers ever on the lookout for ways to minimize their carbon footprint. It is an exciting new frontier and an opportunity in construction to deliver more environmentally responsible projects and meet goals for the future. The fight to reverse the impacts of industrialization on the environment is on and carbon sequestration technology represents an important opportunity.

[5]Nancy Novak, Compass Datacenters’ chief innovation officer, has over 30 years of construction experience and has overseen the delivery of more than $3.5 billion in projects during that time. Novak is actively involved in a number of organizations dedicated to the advancement of woman in business including Above Glass Ceilings (AGC), Women in Government Relations (WGE), Women Construction Owners and Executives (WCOE), The World Trade Center Initiative, Fortune Media’s Most Powerful Women, and the National Woman’s Party. Novak holds a degree in construction engineering and management from San Diego State University.

Source URL: https://www.constructioncanada.net/carbon-sequestration-in-cement-enhances-concrete-construction/

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