By Diana Kightlinger, Built
To determine how to reduce climate impact in the short and long term, Swedish researchers examined in detail a highway project and its associated supply chains.
Like other types of construction, from residential to railroad, road construction has a profound impact on the climate.
Overall, the construction sector accounts for around a quarter of global carbon dioxide (CO2) emissions. The main contributing factors are the manufacture of carbon-intensive structural materials, such as steel and cement, and the heavy transport required to get the materials to site.
With improved energy and climate performance on the user side of the built environment, attention has shifted to the impact of the building process itself.
Recent work in Sweden has offered new insights into reducing these impacts.
Estimates show that civil engineering and public works in Sweden account for a third of annual emissions. This high figure prompted the Swedish Transport Administration (STA) to set a target of zero net greenhouse gas (GHG) emissions by 2045.
STA applies ever stricter climatic requirements in procurement for major projects, materials used and future maintenance. But to achieve its ambitious goals, the work must start now.
Johan Rootzén, a researcher at the Swedish Environmental Research Institute IVL in Gothenburg, said: “We can’t wait any longer to lay the foundations, do the planning, development and scaling up.
To determine the most effective mitigation measures to reduce carbon emissions from construction and industrial supply chains over the coming decades, Mr. Rootzén and his colleague, Ida Karlsson of the Department of Space, Earth and Environment from Chalmers University of Technology, conducted a case study of a road construction project in Sweden.
Build the overview
Many life cycle assessments have assessed the carbon footprint of building roads or parts of them. But few studies have taken a holistic view of options for reducing GHG emissions along the road construction supply chain.
The researchers borrowed their approach from the energy industry, where evaluating scenarios using detailed resource flows and associated environmental impacts is common.
The greatest value of the research is to add a time dimension to see what mitigation measures need to be put in place to meet emission reduction targets when building the same road in five, ten and 25 years.
Map supply chain flows
The project focused on a new 8 km section of national road 44 in central Sweden, the construction of which was completed in 2019.
To determine the sources of GHG emissions, the STA and the contractor used a “Climate Footprint Tool”. This tool calculates energy use and climate impact using emissions factors as well as project-specific resource and input models.
“The tool’s output provided the basis for mapping material and energy flows along the supply chain,” Rootzén said.
This included materials and energy used as inputs for construction materials and energy and fuel for transport and construction services.
The following supply chain activities had the greatest climate impact:
- Production and use of steel
- Production and use of cement and concrete
- Asphalt production and paving
- Heavy transport
- Building process
The research team considered five scenarios, but the main “transformation scenario” consisted of a broad portfolio of reduction measures across all supply chain activities, increasing in scope over time.
Other scenarios tested sensitivity to changes in critical mitigation measures, such as the non-use of biofuels.
Achieve short and long term goals
Immediate opportunities for reduction options include the following:
- Lowering asphalt production temperature and increasing recycling rates
- Use scrap steel
- Use of cement clinker substitutes in concrete
- Conversion to biomass fuels for machinery, transport and production facilities
- Use of hybrid construction equipment
In the long term, emission reduction measures must be intensified:
- Electrifying construction machinery
- Use hybrid or electrified mass and material transport
- Using carbon capture and storage for cement clinker production and steel mill emissions
- Commercialize breakthrough technologies such as direct reduction of iron ore to hydrogen with hydrogen produced by renewable electricity
The Transformative Scenario shows that it is possible to halve GHG emissions using the best technologies available today.
“Nobody is cutting their emissions in half today,” Mr. Rootzén said. “The requirements are still too lax and the bonuses for meeting them are too low. Costs and other barriers also play a role.
Additionally, the Swedish construction industry remains risk averse, with slow adoption of innovation, a challenge seen globally.
The analysis demonstrates that the road construction industry can meet the minimum reduction targets demanded by Sweden. This would mean that public and private buyers must implement measures, including new technologies for the production of cement and steel.
“Procurement requirements are a way to signal that there is a market for low-emission solutions,” Rootzén said.
“We must find solutions to share these risks and the costs of their development.
“What is emerging is the need to prepare now for deeper reduction, to carefully consider the path to get there while avoiding pitfalls along the way. Problems could include an overreliance on biofuels that may be rare in certain regions or cost optimizations that cannot be brought to required levels.
More than half of the urban infrastructure that will exist in 2050 remains to be built, according to the International Resources Committee, which is part of the United Nations Environment Programme.
This projection should mean endless projects for construction contractors, but meeting decarbonization requirements will require all players in the supply chain to work together.
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