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The national CircVol project began in the autumn of 2018 and came to a close at the end of 2020. It brought together companies, universities and research institutions, as well as actors from the public sector. The project was coordinated by Turku Science Park. The common goal was to advance business based on circular economy and to ensure that side streams are utilised in infrastructure projects in cities.
Nordkalk took part in two stabilisation experiments: a field trial concerning stabilisation of dredging masses took place at Matalahti in Naantali, and stabilisation of high-clay content soil of Topinpuisto area in Turku was tested in Nordkalk’s laboratory in Pargas.
“Local activity is important in circular economy projects, because transport increases both costs and environmental impact”, says Thomas Nyberg, Application Manager, who was responsible for the practical arrangements at Nordkalk in both experiments.
R&D Director Mathias Snåre and Application Manager Thomas Nyberg in the laboratory in Pargas, where they were photographed through a device used for measuring compressive strength. Nordkalk offers laboratory services to other companies, too. (Photo Tatu Lertola)
The City of Turku has given up the practice of placing dredged materials in the sea as it can act as a cause of increased euthropication. When the material is put on land and stabilised, it is turned into safe and useful material for earthworks. The field trial was started in April 2020 in Naantali, in the future Housing Fair area at Matalahti. The test field will become a parking area.
In the field trial, different stabilisation mixtures were tested in nine test squares, among them cement, power plant ash and slag. Nordkalk's test material consisted of reactive lime kiln dust (LKD), which accumulates in the electric filters of a lime kiln during the calcination process. LKD was used in three different recipes.
Dredging at Matalahti in Naantali, Finland. (Photo Turku Science Park)
In order to follow the stabilisation level, samples were taken after one week, one month, and three and six months. In the laboratories of Åbo Akademi University and Turku University of Applied Sciences, the compressive strength of the samples was determined. It indicates the bearing capacity of the soil mass. The best initial strength was achieved with the ash-cement-slag mixture, and the mixture in which part of the slag had been replaced by LKD. When the final strength was measured, the LKD mixture reached the second-best result. A mixture recipe is selected depending on the application, and the decisive properties are, e.g., the initial and final strengths, solubility, and the material’s ability to mix with soil.
“The result shows that LKD is suitable for stabilising dredging masses. It means one more application area for LKD, as part of the mixture along with other ingredients”, says Thomas.
At the moment, Turku Science Park is preparing for a continued research through CircVol2 project, during which the carbon footprint of the stabilisation materials will be measured. Åbo Akademi University and the Finnish Environment Institute are in charge of this task. Minimising the carbon footprint is an increasingly important criteria in all procurement.
Share of side streams increasing in stabilisation products
Nordkalk has a decades-long experience in soil stabilisation, and lime-based solutions are suitable for demanding stabilisation projects. For example, Nordkalk Terra GTC is used for stabilising hardening sludges and sulphide clays. The product recipe contains cement and gypsum, and a circular product that is left over from making hydrated lime.
Twenty years ago, Nordkalk Terra GTC was used in the Topinpuisto area in Turku, where the Topinoja waste treatment centre is located. Today, Topinpuisto is developed into a circular economy hub and learning environment, helping companies find new growth opportunities in circular economy.
Thomas Nyberg visions a future where side streams no longer end up as waste. (Photo Tatu Lertola).
The expansion area of Topinpuisto is located on easily sinking clay soil, which was used in the stabilisation test. Different recipes were tested in laboratory conditions. In addition to Nordkalk, three suppliers participated in the test, each with two recipes, based on e.g. ash, slag and cement.
Nordkalk's test product was Nordkalk Terra POZ, of which 43% is recycled material. The product contains quicklime, LKD, and a cement mix including recycled material. This environmentally friendly product was developed as early as 2005, but in recent years it has experienced new interest with the rise of circular economy solutions. The reference material in the test was Nordkalk Terra GTC.
“Terra POZ performed well, meaning that the desired compressive strength was achieved. Hopefully we will be able to continue with field trials later this year, as planned”, says Thomas.
Nordkalk's newest soil stabilisation product is Nordkalk Terra Green, which is still under development. Half of the raw material is LKD and the other half is cement containing recycled material. Thus, the product consists mostly of side streams, which is a step towards developing carbon-neutral products.
Text: Anne Foley
Nordkalk is the leading limestone company in Northern Europe. We deliver essential raw materials to numerous industries, and our solutions contribute to clean air and water as well as productivity of agricultural land.