The building sector is responsible for nearly half of our nation’s carbon dioxide emissions. Although optimizing energy efficiency is important, it is the materials supporting the structure that embody the biggest share of its lifetime carbon footprint. Reducing embodied carbon is important because emissions released over the next 20 to 30 years are critical to keeping global temperatures at tolerable levels.
Compared to other construction materials in terms of embodied energy and carbon dioxide emissions, concrete is the favorable choice. However, the fact remains that concrete has a high carbon footprint due to the energy intensiveness and generation of carbon dioxide in Portland cement manufacturing. Although great strides have been made in improving energy efficiency and minimizing emissions in cement production, carbon-reducing alternatives to ordinary Portland cement are required to achieve further significant reductions in the carbon footprint of concrete.
Due to growing concerns over the environmental impact of building materials, Seattle was the first city to approve the use of Portland Limestone Cement (PLC) for structural concrete in 2015. Approval from the Washington Department of Transportation and other Pacific Northwest markets soon followed.
With a constant emphasis on producing sustainable high-performance concrete, Stoneway Concrete quickly took the lead in using OneCem® Portland Limestone Cement to reduce the amount of clinker in their mixes. Used seamlessly as a direct substitution for ordinary Portland cements, OneCem, part of the Envirocore™ Series, offers the same level of performance and workability as Type I and Type II cements. Because it uses less clinker, carbon dioxide emissions are reduced by up to ten percent per ton of cement.
According to Greg McKinnon, operations manager at Stoneway Concrete, his business no longer uses ASTM 150 Type I/II cement in its concrete products. “Our seamless transition to Type IL cement was a major step in the company’s commitment to reduce its environmental impact and provide the highest quality products in the Seattle market,” he said. “Stoneway Concrete’s use of PLC has resulted in a carbon dioxide reduction of approximately 22,665 tons since 2017, and we estimate it will reduce our carbon dioxide footprint by an additional 15,400 tons annually moving forward.”
Beyond utilizing the greenest cement available, Stoneway Concrete also typically incorporates supplementary cementitious materials (SCMs) in their mixes, such as NewCem® Slag Cement. This partial replacement of Portland cement with SCMs not only allows the company to produce more durable concrete but further lower energy consumption and greenhouse gas emissions. “The optimization of SCMs in our mixes has allowed Stoneway Concrete to further reduce carbon dioxide emissions by more than 51,000 tons since 2010,” said McKinnon.
Over the last five years, projects in the Seattle area have relied on more than 440,000 tons of OneCem to reduce the carbon intensity of concrete mixes. This tremendous usage rate—combined with high replacement levels of SCMs and recycled concrete as aggregate—has made a tremendous contribution to reducing the carbon footprint of the city’s rapidly growing and changing built environment.
By acting, Seattle is not only responding to the threat of climate change but also making its community stronger and economically resilient. Below are some signature projects that have and will continue to make an impact on positioning Seattle as a leader in defining what it means to be a climate-friendly city.
A New Workplace—With a Lower Carbon Footprint
Another iconic resident in Seattle’s business community is addressing the climate change crisis more aggressively, this tech giant has recently committed to remove more carbon than it emits by the end of the decade. Today, a major renovation of its enormous 500-acre campus is underway with the addition of more than two million square feet of new office space—expanding the company’s presence in the Seattle area from 125 to 131 buildings. The company is committed to reducing embodied carbon in the massive campus rebuild by at least 15 percent. To help achieve this goal, Stoneway Concrete is providing sustainable concrete mixes designed with OneCem and NewCem.
A Project That Blends Performance with Sustainability
A major company in Seattle is committed to building a more sustainable future with a focus on emitting less carbon, using less energy and water, and creating less waste. In 2015, the company expanded its Seattle delivery center with three jetways for deliveries of its aircraft to customers. The new heavy airfield concrete pavement can support active aircraft while maintaining the Federal Aviation Administration’s most stringent durability specifications. With a clinker factor of 42, the concrete design included OneCem, NewCem, fly ash and recycled concrete aggregate.
A Strong and Sustainable Expansion
This tech and logistics company’s corporate campus spans downtown Seattle with over 40 office buildings designed to LEED® standards. In 2013, the company added 420,000 square feet of new headquarters space and broke ground on an expansion encompassing several million square feet on four city blocks. Construction utilized high-performance sustainable concrete mixes to achieve a clinker factor of 16 percent, the lowest in the Seattle area. Significantly, the concrete used in the headquarters’ signature “Spheres” was designed with 80 percent NewCem to achieve sustainability goals, 8,000-psi strength requirements, and architectural aesthetic requirements.