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 greenhouse gas emissions from production to quantifying and reducing environmental impacts and costs during the useful lifespans of infrastructure facilities and buildings, and at the end of life.

The Challenge 

While much attention has been given to decarbonizing the transportation and energy sectors, there is a growing challenge in lowering the carbon footprint of the built environment to meet the emissions-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 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 alternative fuel sources, such as biomass for kiln heating instead of coal, or changing 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. Replacing coal will reduce greenhouse gas emissions by approximately 5,000 metric tons of CO2e per year (tpy).

Other technologies for generating the heat required to produce cement are also being explored, including hydrogen-based fuels and electric heaters powered by renewable energy.

Feasibility studies are underway for technologies that combine biomass, hydrogen, and other energy sources to 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 offsite energy, these efforts are reducing the overall volume of carbon emissions associated with cement production.

Carbon capture, storage, and sequestration (CCSS) is another way to reduce emissions from clinker production, as well as to lower the clinker content of cement by blending supplementary cementitious materials (SCMs) 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 has the potential to deliver 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 generate approximately 10% less CO_2, thereby reducing the embodied carbon per ton of cement.

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

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

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

Designers and specifiers can easily specify the use of blended hydraulic cements by calculating and comparing the embodied carbon impacts of materials before consumption using 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 lower volumes of concrete that can be manufactured offsite, or that employ construction techniques such as 3D printing, also holds 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 does designing buildings and communities to better withstand and recover from extreme weather-related incidents, such as floods, wildfires, storms, or heat waves, provide an emissions-reduction benefit.

Increasing the longevity of buildings and infrastructure, improving quality control, and generating and reusing demolition waste will significantly lower GHG emissions over time. Waste product use and reuse provide 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 quantification of the untapped potential of atmospheric CO2 reabsorption (carbonation) by exposed concrete will also alter the balance of carbon accounting for concrete relative to other building products.

Policy Approaches

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

Governments are the key players in infrastructure investments and, as such, can play a profound role in the design, construction, and 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 use are still in their infancy, but have already been legislated in some jurisdictions as a means of offsetting or reducing 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 nutritional label about 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 don’t have time to approach this linearly”, she notes.

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

Other policy measures include public support for clean energy research and development. If coupled with the enormous leverage of government procurement of lower-carbon products and services, this could profoundly change industry behaviour. Tax incentives, grants, loan guarantees, feed-in tariffs, and contracts for the deployment of innovative technology solutions will also drive 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 facilitate the sharing of best-practice information. This process 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 reduce the carbon footprint of the built environment fundamentally and to promote greater resilience 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.

__________________________

William Larson has been the Chairman of the Pacific Northwest Building Resilience Coalition since its inception in October 2016.

Frank Came is the Communications Director of the Pacific Northwest Building Resilience Coalition.