Reducing the carbon footprint of the built environment

By William Larson and Frank Came

Alive to the challenge of climate change, the cement and concrete industries are working to lower the embodied carbon of buildings and infrastructure.

PNBRC July 15, 2020 – Around the world research is underway to address the sustainability and environmental impacts of the production and use of cement and concrete.

These efforts range from adapting the composition of cement and concrete, to reducing the greenhouse gas emissions of production, and quantifying and reducing the environmental impacts and costs during their useful lifespans and the end-of-life of infrastructure facilities and buildings.

The Challenge 

While much attention has been given to decarbonizing the transportation and energy sectors,  there is a growing challenge to lower the carbon footprint associated with the built environment to meet the emission reduction targets of the Paris Agreement adopted by many nations in 2016.

Responding to this challenge, cement and concrete producers around the world are revisiting existing and exploring new technologies to lower the carbon content associated with both the manufacture and use of their products. For some, the goal is to achieve an ambitious net-zero target by 2050.

Speculation varies but it is widely thought that roughly 8% of global GHG emissions come from the industrial processes of cement, iron and steel, and the chemical industries.

Because concrete is the most widely used building product in the world, lowering the energy and carbon footprint of cement production logically is the first place to start.

Changing the way we make cement

Currently, over 4 Gt of cement are produced globally each year, resulting in more than 2 Gt of CO₂ emissions, about 6% of the global total of greenhouse gas (GHG) emissions).

These emissions stem largely from the process of cement manufacturing, which requires extremely high temperatures (over 1,200 °C) in a kiln, as well as from the chemical decomposition of limestone.

Strategies being pursued by leading industry players to lower CO₂ emissions in the cement-making process include introducing other fuel sources such as biomass for the kiln heating process, in lieu of coal, or making changes to the fundamental composition of cement.

Lafarge Canada recently announced a long-term contract to use biosolids as fuel in cement manufacturing at its Richmond British Columbia plant. By replacing the use of coal, this will reduce greenhouse gas emissions by approximately 5,000 metric tons per year (tpy) of CO₂e.

Other technologies for generating the heat needed to make cement are being explored as well,  including the use of hydrogen-based fuels or electric heaters that run on renewable energy sources.

Feasibility studies are underway on technologies that combine biomass, hydrogen and other energy sources that could reduce or eliminate fossil fuel CO₂ emissions.

Coupled with retrofitting older cement production plants and designing new more energy-efficient facilities that reduce the demand for off-site energy the overall volume of carbon emissions associated with cement production is declining.

Carbon capture, storage and sequestration (CCSS) is another way to reduce the emissions from clinker production, as well as lowering the clinker content of cement by blending supplementary cementitious materials (SCM) such as fly ash, or slag (a waste stream byproduct from steel production). These practices are emerging in the industry. Research on alternative binders for cement holds the potential for even greater reductions in carbon emissions.

As an example, CalPortland, a world leader in sustainability, has just launched ADVANCEMENT^TM, a new line of ASTM C595 blended hydraulic cements with up to 15% limestone by mass, that generates approximately 10% less CO₂ thereby reducing the embodied carbon per ton of cement.

Certain blends of the product line can reduce the amount of CO₂ in the manufacturing process by as much as 20-25% as compared to Ordinary Portland Cement (OPC) while maintaining product performance requirements.

Several other cement manufacturers in the U.S. and Canada, such as Lehigh Hansen, also manufacture ASTM C595 blended hydraulic cements that reduce CO₂.

The beauty of this technology is that the product is available now and, in most cases, can be specified in lieu of OPC without sacrificing performance characteristics. Additionally, ASTM C595 blended hydraulic cements may be used in conjunction with other concrete GHG mitigation strategies leading to even greater CO₂ reduction.

Designers and specifiers can easily specify the use of blended hydraulic cements as they calculate and compare embodied carbon impacts of materials prior to consumption through the various tools available today.

How we use cement and concrete in the built environment is also an area ripe with carbon-reducing potential.

Changing how we use cement and concrete

Apart from changes to the actual composition of cement, changing how cement and concrete are used can also lower the carbon footprint of the built environment.

Optimizing the design of structures to be more energy-efficient, more resistant to climate-related impacts, and more price-competitive in the marketplace would greatly influence the development and affordability of housing in our rapidly expanding cities and towns.

Designing buildings or infrastructure that require lesser volumes of concrete that can be manufactured offsite or that employ construction techniques such as 3D printing technologies also hold great promise.

More climate-resilient concrete could lengthen the useful lifespan of buildings, thereby lowering the dollar and carbon costs of replacement or renovation. So too, designing buildings and communities to better withstand and recover from extreme weather-related incidents such as floods, wildfires, storms, or heat waves also provides an emissions reduction benefit.

Increasing the longevity of buildings and infrastructure, improving quality control and the generation and reuse of demolition waste will significantly lower GHG emissions over time. Waste product use and reuse provides additional opportunities as substitutes for fossil fuels and raw materials, which also addresses our waste problem as a society.

The elimination of typical construction/demolition waste materials such as wood and petroleum-based products from our landfills can provide an environmental credit rather than a debit when viewed from the perspective of the circular economy.

Growing recognition and calculation of the untapped potential of atmospheric C0₂ reabsorption (carbonation) by exposed concrete will also alter the balance in carbon accounting for concrete relative to other building products.

Policy Approaches

While many technological approaches are being explored to lower the embodied carbon of buildings and infrastructure assets such as roads, bridges and transportation facilities, policy and regulatory measures are also being deployed as well.

Governments are the key players in infrastructure investments and as such can exert a profound role in the design, construction, and the operation of public facilities through permitting financing, and other associated policy measures.

Measuring the embodied carbon content of various building materials is rapidly becoming an important tool for the design and regulation of structures. The various carbon calculator tools in play are still in their infancy but have already been legislated in some jurisdictions as a means to offset or lower carbon emissions. Lifecycle Assessment (LCA) tools of varying sophistication are being used to formulate embodied energy or carbon indices.

As noted by Dr. Jeremy Gregory, the Executive Director of the Concrete Sustainability Hub at MIT Environmental Product Declarations amount to a nutritionalabout a product’s environmental impact. Until recently, creating EPDs required several months of independent, individual verification, and was very time-consuming and expensive.

According to Kate Simonen, a co-founder of the Carbon Leadership Forum, embodied emissions—those released from the manufacturing of industrial materials are going to rise, at least as a percentage of the overall impact.

“As building codes become more stringent and the electrical grid decarbonizes, the relative proportion of impact due to material production increases.  We simply don’t have time to approach this in a linear fashion”, she notes.

For example, prohibiting or limiting fossil fuel use or requiring lower carbon-intensive technologies could stimulate profound changes in business practices.

Other policy measures include public support for clean energy research and development. If coupled with the enormous leverage of governmental procurement of products and services with lower carbon content this could profoundly change industry behaviour. Tax incentives, grants, loan guarantees, feed-in-tariffs, and contracts for the deployment of innovative technology solutions also will stimulate change.

Summing Up

The stark realities of the need to reduce the carbon content of the built environment have not been lost on key players in the cement and concrete industries,  nor by policymakers at all levels of government.

Working in partnership with industry associations can strengthen the drive for decarbonization and the sharing of information on best practices. This is a process that requires open dialogue and a willingness to work cooperatively.

Many industry associations have come together to articulate clear messages for policymakers on practical approaches to fundamentally lower the carbon footprint of the built environment and to promote greater resiliency and risk reduction.

While there is no shortage of ideas to meet this challenge, the window of opportunity is very tight. Major investments in new technologies and sound public policies that place a premium on resiliency, efficiency and sustainability are needed now. Time is not on our side and as history has shown us over and over again, time waits for no one.

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William Larson is the recently retired Vice President Marketing at CalPortland. He also serves as Chairman, of the Steering Committee coordinating the development of the Pacific Northwest Building Resilience Coalition since its inception in October 2016.

Frank Came is Managing Director of Globe Advisors. He was the Project Director for the Globe Advisors study on Carbon Sequestration of Forest-Based Wood Building Products completed in 2017 for the Pacific Northwest Building Resilience Coalition.