Posted on September 21, 2023
Concrete is a superior construction material in myriad applications. Its prodigious durability, strength, versatility, and modest cost make it the material of choice for dams, roads, bridges, skyscrapers, water systems, and much more.
Low-carbon concrete addresses a key challenge: significant CO2 emissions generated mostly in the production of ordinary Portland cement (OPC). Portland cement is concrete’s most carbon-intensive ingredient, by far. Producing one ton of OPC generates emissions equal to those generated by a passenger vehicle traveling 1,500 miles. As a result, concrete is typically responsible for 50-85% of the embodied carbon in a construction project.
In 2020, the Global Cement and Concrete Association made its Climate Ambition Pledge, encouraging producers to commit to carbon neutrality by 2050. Similarly, architects, contractors, and project owners respond to rising sustainability expectations of end users. There are a growing number of initiatives, including:
A global embrace of low-carbon concrete is essential to meet such ambitious goals.
Low-Carbon Concrete: The Possibilities
Low carbon concrete is concrete produced with a lower carbon footprint than its traditional counterpart, but without compromising essential properties like compressive strength and durability.
One contributor to reduced emissions is the exposed concrete already in place across the planet. Concrete, water, and CO2 (in the air) combine to form a mineral, calcium carbonate. This carbonation process sequesters CO2 in concrete. Every year, worldwide carbonation removes an equivalent of half the CO2 emitted during that year’s cement production. Of course, that is not enough. The concrete industry is now committed to nothing less than carbon neutrality, long-term.
An expanded use of supplementary cementitious materials (SCMs) reduces emissions. There are various low-carbon mixes like LC3 and ECOPlanet cement. LC3 makes use of locally sourced SCMs like calcined clay (metakaolin). For example, one LC3 mix is half clinker, 30% calcined clay, 15% limestone, and 5% gypsum. In the future, researchers hope to reduce clinker content to as low as 30%. By comparison, Portland cement is approximately 91% clinker, and Portland limestone cement (PLC) is about 83%.
Holcim’s ECOPlanet cement “delivers 100% performance starting at 30% lower CO2 emissions” compared to OPC. ECOPlanet cement has been used in various high-profile projects, like The Spheres in Seattle. Its Living Walls include 25,000 plants woven into a 4,000 sq ft wall. Cairo’s Iconic Tower also uses ECOPlanet cement. At 1,392 feet, Iconic Tower is Africa’s tallest building.
One study concluded that it was possible to reduce the carbon emissions of a new five-story building by 32%. Researchers concluded that the reductions increased construction costs by less than 0.5%. However, low-carbon concrete does present certain challenges. Examples include increased setting times and reduced early strength. Together, these factors can increase project timelines.
Reduced Emissions Through Engineering and Design
Advanced engineering and design maximizes the emissions impact of low-carbon concrete.
Innovative design yielded a 40% reduction in concrete use in the Freedom Tower. Eastern Concrete Materials produced about 150,000 cu yds of high-strength concrete for the Freedom Tower’s superstructure. Collavino Construction pumped the mix as high as 103 stories.
Concrete strength was enhanced with an additive called iCrete. It consists of a select blend of microminerals conforming to ASTM-C 1797. iCrete reacts with certain cement phases to increase strength and durability. Common dosages range from 0.70 to 2.25%.
Case Studies in Low Carbon Concrete
We’ll discuss three projects where the type of concrete mix significantly reduced emissions. We’ll also discuss a company that installed CarbonCure technology at its plants.
725 Ponce Street, Atlanta
Contractors completed the 547,000 sq ft, 16-story office building at 725 Ponce Street in 2019. The structure features the widespread use of exposed concrete. The higher office floors step back, creating multiple outdoor roof terraces. The structure was awarded the American Concrete Institute’s 2020 second place national award in the mid-rise category.
Uzun+Case specified the use of low carbon concrete. Thomas Concrete used CarbonCure tech to divert 680 tons of carbon emissions from the atmosphere. This is an amount equivalent to the amount removed by about 888 acres of forest in a year.
725 Ponce Street is one of the largest structures to embrace CarbonCure technology. The low-carbon strategy contributed to the project’s LEED Silver certification.
Infosys Technology and Innovation Hub
The result is the Infosys Technology and Innovation Hub, a 125,000 sq ft state-of-the-art training center. For the project, Infosys hired Browning Construction to revitalize and develop a 70-acre site on the west side of Indianapolis, IN.
Browning embraced Carboncure’s tech for the project, noting how it aligns with Infosys’ core values and corporate culture. For the project’s first phase, Irving Materials delivered a variety of concrete mixes infused with carbon dioxide. Ultimately, it delivered a total of 8,000 cu yds of 3,000, 4,000, and 8,000 psi mixes.
Lauren Concrete
Lauren Concrete's four Texas plants use CarbonCure technology. It permanently sequesters CO2 by injecting it into concrete mixes. The company embraces other emissions reducing strategies like:
Fleet optimization using GPS tracking
Real-time quality monitoring
Expanded use of sensors that track temperature and strength
Thus far, Lauren Concrete’s emissions-saving efforts have saved more than 6,400 tons of CO2.
Meta data center in DeKalb, Il
There are approximately 8,000 data centers in the world, with about a third located in the United States. By 2025, they will consume about one-fifth of the world’s power supplies. Data centers are housed in huge concrete structures. The largest data center in the world is China Telecom’s 10.75 million sq ft facility in Hohhot, China. Nevada's Citadel Campus encompasses more than 7.75 million sq ft. Researchers collaborated to reduce the project's concrete carbon emissions by 40%.
About PACA
The Pennsylvania Aggregates and Concrete Association (PACA) reports on industry innovation through its Specifyconcrete.org website. The PACA team welcomes questions about your upcoming concrete project. Please contact us at your convenience!
