Siirry suoraan sisältöön

Helsinki is developing solutions for carbon-neutral earthworks

Helsinki is experiencing both the peak years of housing construction and a significant reduction in greenhouse gas emissions. Helsinki will become a carbon-neutral city by 2030, and the climate goals will also be taken into account in preconstruction and infrastructure construction. The city has boldly embarked on various research and pilot projects to develop low-carbon solutions for the entire construction sector.

In Helsinki, new residential areas usually rise on demanding soils, such as reclaimed land or shores. Before buildings can be constructed, the land must be prepared for construction by means of preconstruction. In addition to the restoration of contaminated soil, demolition of old buildings and reinforcement of soft soil, the necessary technical infrastructure is built.

Circular economy methods were tested for the first time as early as in the 1970s, when the city began to study the utilisation of coal combustion ash. This makes Helsinki a pioneer in sustainable infrastructure construction. Helsinki not only invests in minimising emissions in its own operations, but also offers new opportunities for research and product development. There is close cooperation with both companies and communities.

The city can grow, emissions cannot

In an ever-growing city, surplus materials are constantly being formed and, on the other hand, earthworks require hundreds of thousands of tonnes of soil and rock and various building materials, most of them virgin materials. Soil and rock materials and their transport cause the highest emissions and costs in infrastructure construction.

Completely zero-emission construction is impossible, but many solutions are being developed in Helsinki to minimise the carbon footprint. Since 2014, Mikko Suominen has been considering the city’s circular economy activities in his work as Land Mass Coordinator. The work of the land mass coordinator includes, among other things, the recycling of land masses from various construction projects, from the early stages of planning to implementation, maintenance and demolition.

“Our goal is to utilise demolished concrete from buildings, for example, as efficiently as possible in infrastructure construction, and thereby replace virgin material: crushed rock. This will also reduce the need for transport. The utilisation is very challenging within Ring III due to limited recycling areas and tight project schedules,” Suominen says.

Suominen’s career with the city began with extensive regional construction projects, such as the West Harbour project area. Over the past decade, Jätkäsaari and Hernesaari have expanded by 25 hectares with massive land reclamation. There are many examples of mass recycling in the area. Beneath the highest hill of Hyväntoivonpuisto Park, there is encapsulated contaminated soil excavated from Jätkäsaari in an amount corresponding to the volume of the Parliament House. Land reclamation has been made using both crushed rock from the West Metro and demolished concrete formed in the area.

“It has been very sensible to use the old port areas for residential purposes. This way, green areas are saved and biodiversity is taken care of,” says Suominen.

Good planning saves nature and money

An estimated 15 million tonnes of soil are transported annually in the Helsinki Metropolitan Area, and transport is the largest single cost and environmental burden in the use of soil. More than 90% of emissions from infrastructure construction are solved at the planning stage, especially in the case of land use. Mikko Suominen emphasises the importance of information on the road to carbon neutrality.

“In every project, it is important to understand where the biggest emissions come from. If we don’t focus on the big things, we will fall further behind the goals,” Suominen says.

One of the sources of such information is Massatyökalu, a GIS-based land mass tool developed for land mass management, which was used for collecting data about more than 70 projects last year. The land mass tool can be used to optimise mass transport, thereby reducing both emissions and costs. Helsinki has also opened the data collected in the land mass tool for use by other operators, so that mass coordination can be developed nationally.

The city is also involved in other projects promoting low-carbon infrastructure construction, such as the building of the infrastructure construction emissions database led by the Finnish Transport Infrastructure Agency. The aim is to develop a unique database at international level, which will allow emissions from infrastructure construction to be calculated as accurately as is already possible in housing construction.

“Preconstruction and infrastructure construction are slightly lagging behind and are usually not even taken into account in emission calculations. But precise emissions data is needed to support good decision-making. We must also take into account that, for example, emission reductions from land mass coordination will be achieved immediately, not just over the decades,” says Suominen.

In 2021, good planning in Helsinki considerably saved both the environment and construction costs. In total, 1.5 million tonnes of excavated land mass and rock materials were used in the construction of public areas, saving €8.5 million. The emissions decreased by 2,600 tonnes of CO2. This corresponds to approximately 9,000 flights from Helsinki to Munich and back.

The city is a place of development and experimentation

In addition to the city’s own construction projects, Suominen, who has been nicknamed “Massa-Mikko”, works on national projects that aim to make low-emission alternatives an everyday part of construction. One example of these is the UUMA4 programme, which is a forum for cooperation to increase the use of recovered materials in earthworks.

“Preconstruction has good opportunities to influence emissions through the selection of the binder for deep mixing, for example. Traditionally, lime cement used in deep mixing produces up to ten times more CO2 emissions than binders based on recovered materials,” says Juha Forsman, UUMA4 Programme Coordinator and Division Manager of Geotechnical Engineering at Ramboll.

There is plenty of soft clay soil in Helsinki, as in all coastal cities. For this reason, preconstruction is often started by reinforcing the soil. One method is deep mixing, in which a binder is added to soil with poor load-bearing capacity in order to improve it. For example, the areas of Arabianranta and Fallkulla have been made safely available for use by deep mixing.

Helsinki has been actively involved in the search for alternatives to emissions-intensive binders and has provided a valuable platform for experimenting with various low-emission materials. Two years ago, a trial deep mixing project was carried out in Kuninkaantammi with six binder recipes based on recovered materials. In real-life conditions, the testing produced a wealth of new information on the technical properties and functionality of low-carbon binders.

“Although recovered materials are tested in rigorous laboratory tests, the test structures and actual construction sites give a more realistic picture of how the materials behave. At the same time, material logistics is tested, for example,” Forsman says.

The environmental impacts are also studied at pilot sites. Environmental permits, which are a precondition for construction, require careful plans and strict monitoring programmes. In Helsinki, the emissions and impacts of construction are monitored at all sites, not just when testing new materials and methods. For example, groundwater pipes installed in construction sites ensure that the quality of the water does not suffer from construction.

Alakivenpuisto. Photo Sofie Jokinen.

New operating models require open-mindedness

Waste incineration ash in roadside noise barriers, contaminated soil encapsulated beneath a park? When it comes to utilising the last side streams from production and waste management, local inhabitants may be sceptical about the new ways of working.

Leena Korkiala-Tanttu, Professor of Geoengineering at Aalto University, knows that prejudices against materials sometimes lead to complaints.

“People may be worried if ash or waste slag is used nearby. However, they are useful materials and there is no need to be afraid of them. Their environmental acceptability has been ensured, and the emissions are small, if they even exist,” Korkiala-Tanttu says.

Korkiala-Tanttu praises Helsinki as a pioneer in the use of recovered materials in earthworks. One of the most recent experiments carried out in cooperation with the city is the noise barrier built in Konala, which tests the method of packing soil, dating from thousands of years ago, this time using fine slag from waste incineration and crushed concrete. Finding use for both materials has been challenging, but now the test structures tailored for Helsinki can be used to determine their suitability for construction.

Using recycled materials, the carbon footprint of construction can be reduced by several tens of percent at best. In order for new materials and operating models to become more common in construction, someone must set an example.

“The climate is getting warmer and warmer, and we should act quickly. A lot of work is done in Helsinki to get the right information and select the measures that can best affect emissions from earthworks and infrastructure construction,” Juha Forsman says.

Text: Milla Palkoaho

Laura Yli-Jama, Head of the Environment Unit at the Finnish Transport Infrastructure Agency, was also interviewed for the article.

A former landfill, Vuosaarenhuippu is now a popular outdoor recreation area and nature site. The total volume of the surplus masses used for the rehabilitation of the municipal waste landfill in its western part is eight times the volume of the Parliament House. Photo: Juha Nurmela.

In Myllypuro, a former landfill area was rehabilitated as a park, utilising materials such as sea-bottom soil from Jätkäsaari and excavated soil from Kivikko. Photo: Sofie Jokinen.