Stockholm Royal Seaport

Sustainability Report

Climate-reduced concrete tested in pilot project

The construction of facilities leads to significant climate impact during the construction phase, partly from the production of materials, and partly from the construction process as a whole. To minimise the climate impact, measures must be taken during both the design and construction phases. One approach is to test various concrete mixes by replacing portions of the cement with blast furnace slag. In Stockholm Royal Seaport, pilot projects are underway to explore different concrete mixes for structures both on land and in water.

The City of Stockholm imposes climate requirements for concrete and steel in all contracts, while also initiating research and development to advance the use of climate-improved concrete. Concrete is used as a building material in a variety of structures on public land, but the production of concrete and cement causes high carbon emissions. Replacing parts of the cement with blast furnace slag (GGBS) in concrete is one way to reduce the material's climate impact, which has now been tested in the Ropsten and Värtahamnen phases.

Pile deck in Ropsten with a construction crane in the background
In a temporary pile deck for Lidingöbanan, various concrete mixes are being tested, in which parts of the cement are replaced with slag.

Temporary pile deck at Lilla Lidingöbron

At the land connection of the Lilla Lidingöbron, the Stockholm Royal Seaport development is responsible for a new piled slab with pedestrian and bicycle paths, as well as rail traffic. Before investigations, plans, and designs are complete and the new Ropsten station can be built, rail traffic between Lidingöbanan's existing stop and the new track position on the bridge is directed via a temporary piled slab. Given that the temporary pile deck will only be used until the new station is built, there was an opportunity to push the boundaries with a mix containing a high amount of blast furnace slag. The other mixes will be tested through continuous sampling of large concrete cubes (1x1 m) that will be submerged in the waters of Värtan for an extended period. The tests involve reducing cement against slag (GGBS – Granulated Blast Furnace Slag) by 35, 50, and 65 per cent and are conducted in different structural parts. For the permanent pile deck, 20 per cent of the cement has been replaced with blast furnace slag, while for the temporary one, 50 per cent. Over several years, the project can evaluate how concrete can be made in a more environmentally friendly and climate emission reducing way while maintaining technical properties. The initial indications are that characteristics such as compressive strength and frost resistance are comparable to regular concrete. The results will be documented in a separate report prepared by Swerock.

The pilot project was initiated by the City Development Administration, the Traffic Administration, Peab, and concrete supplier Swerock.

Climate-reduced concrete is tested at Saltkajen

In preparation for the expansion of Saltkajen in Värtahamnen, climate-improved concrete is also being developed for underwater structures with so-called UV concrete. To ensure quality, the tests are first performed in a laboratory and then on a full scale in water-filled containers. Due to varying amounts of slag mixtures, the carbon dioxide load can be reduced by 30 per cent. The project started in 2023.

To date, only a small number of tests have been conducted for this type of concrete in underwater environments, and there is a lack of experience in casting underwater concrete with slag admixture. The tests are part of the development work, and the ongoing Saltkajen project provided an opportunity to carry out mock-up tests with slag admixture. Based on these tests, we can then proceed to implementation in future projects.

Saltkajen is located in an exposed area, and the concrete used for the construction of the new pier will be both below and above water surface depending on weather and water levels in Lilla Värtan. This places special demands on the concrete. The pilot project was initiated in the autumn of 2022, with several tests conducted in the laboratory, which provided several insights. These insights have been applied to the full-scale tests in water-filled containers in Södra Värtahamnen, which began in February this year. A total of three full-scale models are being produced during the spring, with the difference between them being the amount of slag admixture - ranging from 12 per cent to 42 per cent. Ongoing tests on the concrete are evaluating different mixtures to and ensure quality, including studying frost and pressure resistance as well as heat development. The ambition is to reduce carbon dioxide emissions by approximately 30 per cent.

Luc Pagés, the facility engineer, talks about the project. (Swedish only)

To have enough time to test and evaluate the results from the trial casting conducted in the pilot project, the concrete from these tests will not be used in Saltpiren but in future projects. Carbon-reduced concrete that has already been proven will be used for Saltpiren.

As both the demanding party and custodian of what is being built, the City of Stockholm has a unique situation. This entails a responsibility to, under controlled conditions, experiment and push boundaries to find new sustainable solutions. Reducing the climate impact of concrete is one of these solutions.

The project involves the Development Administration, the Traffic Administration, Sweco, and Skanska.

Two people in high-visibility clothing working on top of a container structure.
Testing is underway in Värtahamnen
Three construction workers filling a smaller container structure with slag-mixed, carbon dioxide-reduced concrete.

Article Published: 19/10/2022 Updated: 10/06/2024