Like other types of construction, from residential to railway, building roads profoundly impacts climate.
Overall, the construction sector accounts for about one-quarter of global carbon dioxide (CO2) emissions. The main contributing factors are manufacture of carbon-intense structural materials, such as steel and cement, and heavy transport needed to bring materials on site.
With energy and climate performance improving on the user side of the built environment, focus has shifted to the impact of the construction process itself. Recent work in Sweden offered new insight into reducing those impacts.
Estimates show civil engineering and public works in Sweden account for one-third of annual emissions. That hefty number prompted the Swedish Transport Administration (STA) to set a goal of no net greenhouse gas (GHG) emissions by 2045. STA is applying ever more strict climate requirements in procurement for major projects, materials used and future maintenance. But to reach its ambitious goals, work must start now.
“We cannot wait any longer to lay the foundation, do the planning, development and scale up,” said Johan Rootzén, Ph.D., researcher at the IVL Swedish Environmental Research Institute in Gothenburg. To determine the most effective mitigation measures for reducing carbon emissions from construction and industry supply chains over the next few decades, Rootzén and his colleague, Ida Karlsson of the Department of Space, Earth and Environment at Chalmers University of Technology, conducted a case study of a Swedish road construction project.
Building the big picture
Many lifecycle assessments have evaluated the carbon footprint of road construction or elements of it. But few studies have taken a comprehensive view of options to reduce GHG emissions along the entire road construction supply chain. The researchers borrowed their approach from the power industry, where assessing scenarios using detail resource flows and associated environmental impacts is common.
The greatest value of the research is adding a time dimension to see what mitigation measures must be in place to meet emission reduction targets when constructing the same road in five, 10 and 25 years.
Mapping supply chain flows
The project focused on a new 8-kilometer section of National Road 44 in the middle of Sweden, with construction completed in 2019. To determine the sources of GHG emissions, the STA and contractor used a “climate foot printing tool.” This tool calculates energy consumption and climate impact using emissions factors along with resource templates and project-specific inputs.
“The output of the tool provided the basis for mapping the material and energy flows across the supply chain,” Rootzén said. That included materials and energy used as input for construction materials and energy and fuel for transport and construction services. The following supply chain activities had the greatest climate impact:
- Steel production and use
- Cement and concrete production and use
- Asphalt production and paving
- Heavy transport
- Construction processes
The research team considered five scenarios, but the main “transformative scenario” consisted of an extensive portfolio of abatement measures across all supply chain activities with scope increasing over time. Other scenarios tested the sensitivity to changes in critical mitigation measures, like not using biofuels.
Achieving short- and long-term goals
Immediate possibilities for abatement options include the following:
- Lowering asphalt production temperature and increasing recycling rates
- Using scrap-based steel
- Using cement clinker substitutes in concrete
- Converting to biomass-based fuels for machinery, transport and production facilities
- Using hybrid construction equipment
Over the long term, measures to reduce emissions must ramp up:
- Electrifying construction equipment
- Using hybrid or electrified mass and material transport
- Employing carbon capture and storage for cement clinker production and steel plant emissions
- Commercializing breakthrough technologies like hydrogen direct reduction of iron ore with hydrogen produced by renewable electricity
The transformative scenario shows that it’s possible to cut GHG emissions in half using today’s best available technologies. Still, “no one is cutting emissions in half today,” Rootzén said. “The requirements are still too lax and the bonuses for achieving them are too low. Costs and other barriers also play a role.”
The Swedish construction industry, moreover, remains risk-averse, with slow adoption of innovation, a challenge experienced globally.
The analysis demonstrates that the road construction industry can meet the minimum reduction targets Sweden requires. Doing so would mean both public and private procurers need to implement measures, including novel technologies for cement and steel production.
“Procurement requirements are one way of signaling that there is a market for lower emissions solutions,” Rootzén explained. “We have to come up with solutions to share those risks and the costs of developing them.”
“What emerges is a need to prepare for deeper abatement now, to carefully consider the pathway for getting there while avoiding pitfalls along the way,” Rootzén added. “Issues could include over-reliance on biofuels that may be in short supply in some regions or cost optimizations that cannot be scaled up to the required levels.”
More than half of the urban infrastructure that will exist in 2050 has yet to be built, according to the International Resource Panel, which is part of the United Nations Environment Program. That projection should mean endless projects for construction contractors, but meeting requirements for decarbonization will require everyone in the supply chain to work together.