Clark Construction has turned to low-carbon materials and new technology to build Metropolitan Park, the first phase of Amazon's HQ2 project in Arlington, Virginia.

Amazon wanted to reduce the project's embodied carbon by 10%, and Brian Earle, principal at Portland, Oregon-based ZGF Architects, accepted the challenge. The project site will have 200,000 cubic yards of concrete overall, according to an Amazon fact sheet. Currently, the project is on track to have a 15% reduction in the carbon footprint of the building.

The team is building with a product called CarbonCure, which injects a precise dosage of captured carbon dioxide into the concrete during the mixing process, where it mineralizes. The added carbon dioxide improves the concrete's compressive strength, optimizes the mix and significantly reduces carbon footprint without compromising the structure, according to CarbonCure's website. The mineralized carbon dioxide will never leak out or return to the atmosphere, according to the company, even if the concrete is demolished.

Concrete is the second-most consumed material in the world after water, according to a 2014 study, and construction uses twice as much concrete as all other building materials combined. It's also a massive polluter, responsible for about 8% of all carbon dioxide emissions, according to a 2019 study.

"In targeting concrete as the best way to [reduce carbon], we always knew that we had to hit higher than that percentage in concrete," Earle said. "With other materials, it's harder to realize those savings."

The build celebrated its topping out in March, and Amazon has dedicated $2.5 billion to the project over the next 10 years, according to a company fact sheet. The massive mixed-use development will include two 22-story-tall office buildings, 50,000 square feet of retail space and a two-acre public park.

Tech programs

Despite pandemic and supply chain-related challenges, Brian Krause, vice president at Clark Construction, said technology helped keep the project on track.

"What's been the successful mix on HQ2 is using a lot of technology to identify issues early, resolve them in a digital means, and then working with the project team to execute them in revising our plan, and executing the work in an efficient way," Krause said.

The team adopted products such as CraneView by Versatile, which aided with safety and production, according to Krause. The team also leveraged a variety of data capture tools to keep their jobsite data clean and up-to-date, such as Matterport's software for virtual walkthroughs, OxBlue's software and usage of webcams for progress monitoring on the jobsite, and Assemble's software for quantity planning and production analysis, according to a spokesperson for Clark Construction.

"We've used a lot of technology, but it's that marriage between using the technology, giving the right data to the field team, and then the field team knowing how to act and executing on the information coming from that technology," said Krause.

Mass timber and sustainability

HQ2 will also feature mass timber, an environmentally friendly building material that is gaining steam in the U.S. About 1,384 mass timber buildings were either built or in design in all states since 2013, according to mass timber group WoodWorks.

HQ2's 700-person capacity event space will be built with 14,000-pound timber beams. The building would have four to five times less of a carbon footprint than a concrete building, according to Earle. There are challenges in bringing a mass timber building to market, in particular because owners are hesitant to try new materials. Earle said that the usage of mass timber was meant to showcase the material.

"If we're building 50-year facilities, our clients want a proven track record that something's going to work. By finding those test cases to prove them out, that's the most important step in bringing them to market," Earle said.

Earle also emphasized the unusually large impact that the project has already had on the local market. Both of the project's concrete suppliers, Vulcan and Miller & Long, are now "experts" with CarbonCure along with Clark Construction, according to Earle.

"We're starting to see that growth in the market, and with every project, trying to take it a little further," Earle said.

Correction: In a previous version of the article, the names of the two local concrete suppliers were inaccurate. The two local suppliers are Vulcan and Miller & Long.