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The results of the pilot sections Narva-Mustajõe and Simuna-Vaiatu construction, built with oil shale ash produced in the Narva Power Plants of Eesti Energia, confirmed that oil shale ash is suitable for use in the construction of roads.

The technical and environmental monitoring surveys, conducted as a part of the pilot project between 2012 and 2016, revealed that both of the test sections constructed with oil shale ash have high strength and road-bearing capacity parameters. There was no decomposition of the constructed layers emerged during the monitoring period on both test sections as well as no negative environmental impacts have been noticed.

“The pilot project confirmed that oil shale ash has good stabilising and binding properties and can be therefore successfully used in substituiton of cement,” said Margus Vals, Member of the Management Board of Eesti Energia. In the first stage of the project, the ash was used in the construction of the stabilising layer beneath the asphalt on a 1.6-kilometre section of Narva-Mustajõe road. In the second stage, 900-metre section was constructed in Simuna-Vaiatu road. The oil shale ash was used in mass-stabilisation of the peat layer.

“Oil shale ash has been used successfully in road construction in Estonia before, and these roads have proven to be durable. In the frames of the pilot project the oil shale ash was for the first time tested in modern mass-stabilisation technology. The possible impacts on the environment were also checked. As the results are promising, in the next step we are going to standardize the ash as a product. This will enable the larger quantities of the product to be used in base layer stabilisation and mass-stabilisation in Estonia and abroad. In this way we can add more value to oil shale by offering a quality product at a competitive price to road constructors and reducing the use of non-renewable materials in the construction of roads and ports,” added Vals.

Narva-Mustajõe and Simuna-Vaiatu pilot sections were built within the framework of the OSAMAT (Management of Environmentally Sound Recycling of Oil Shale Ashes into Road Construction Products) project, aiming to facilitate the wider use of oil shale ash generated during production of electricity. According to Taavi Tõnts, Lead Engineer in the Road Network Development Department of the Estonian Road Administration, the OSAMAT project can, in general, be regarded as successful. “Based on the research and tests conducted, we now know that it is technically possible to use oil shale ash also from fluidised bed boilers for mass-stabilisation, in addition to cement. For example, along the new section of the Tallinn-Tartu-Võru-Luhamaa Highway, we have already had planners who consider the mass-stabilisation as one of the alternatives for crossing peat bogs in their comparative technical economic analyses. On roads with lower traffic volumes, we are planning to approve the use of weak stone material (coming from oil shale enrichment) in complex stabilisation. Due to such researches we have a possibility now to use energy production by-products in road construction. Economic efficiency should be assesed separately in the case of each project,” said Tõnts.

The pilot project has been carrying out between 2010 and 2016. The parties of the project are Eesti Energia, Nordecon, Ramboll and the Estonian Road Administration. The cost of the project is EUR 2.4 million and it is supported by the European Union programme LIFE+ for the co-funding of environmental projects. Oil shale ash has been used in road construction before, between 1971–1986 in Estonia, Latvia, Lithuania, Belarus and Russia. In this period more than 1000 kilometres of roads were constructed with oil shale ash. The ash was also widely used for the reinforcement of embankments when the impovements in crushed stone quality and other fillers were needed.