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. The development of public spaces requires substantial amounts of structural concrete. In Stockholm Royal Seaport, several pilot projects using low-carbon concrete have been implemented to reduce climate impact. These pilots examine the durability of concrete with various mix designs, specifically testing different proportions of blast furnace slag as a cement replacement.

The City of Stockholm imposes climate requirements for concrete and steel in all contracts. 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. One pilot project involves a temporary pile deck, while the other focuses on underwater concrete.

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. 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.

As reference samples, concrete cubes (1 x 1 m) with varying slag content have been cast. These will remain submerged in the waters of Lilla Värtan for an extended period. The cubes were cast using three different concrete mix designs where the cement content was replaced with 35, 50 and 65 per cent slag (GGBS – Ground Granulated Blast-furnace Slag).

Over several years, the project will 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 initial short-term test results are documented in a separate report prepared by Swerock. Long-term tests will continue until the temporary structure is demolished.

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

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.

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. Concrete at the waterline is particularly vulnerable. The pilot project was initiated in the autumn of 2022, with several tests conducted in the laboratory, according to standard testing protocols. These insights have been applied to the full-scale tests in water-filled containers in Södra Värtahamnen, which began in February 2022. A total of three full-scale models are being produced during spring 2023, 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.

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.

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

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.

Article Published: 19/10/2022 Updated: 07/10/2026