Helsinki - "Energiantuotannon tuhkien jalostaminen maarakennuskäyttöön" is a project of the Technical Research Centre of Finland (VTT). The core of the project is research on the "Processing of fly ash for earth construction".

Its key findings are published in the following abstract:

The aim of this project was to refine energy production ashes to high-quality products for earthworks. Fly ash samples were collected from different power plants and their environmental and technical applicability for earthworks were determined. Also the possibilities to improve properties of ashes by refining
were investigated.

None of the analysed ash samples fulfilled the requirements of Government Degree (591/2006) concerning the recovery of certain wastes in earth construction. Peat-wood ashes were close to the limit values and they were selected for further investigations. Refining of peat-wood ashes was performed by air classification. In air classification process the small particles that contain high concentration of harmful substances are separated from the coarser ash fraction. Classification improved the environmental and technical applicability of ash for earthworks.

Calculation of costs indicated that the classification of ash can be economically profitable if the alternative is the landfilling of the entire ash amount of a power plant. Annual total costs for ash refining are about half of the landfilling costs, if the yield of coarser ash fraction is 60 %. Life cycle environmental load of the developed ash refining concept was estimated by comparing road structures, in which coarse ash fraction and untreated ash are used in various ways. A road structure made of natural materials was used as a reference. In road structures including fly ash the need for natural materials and fuel was reduced, but the energy consumption and emissions to air were increased. On the basis of life cycle survey the studied road structures can not be arranged into a particular order. The result of comparison is determined
according to the effects which the decision-maker considers to be the most significant.

The possibilities to facilitate recycling of ashes by productisation according to End of Waste-procedure, enabled by EU’s new waste directive (2008/98/EC), were also reviewed in this project. The usage of products is not officially supervised equally to waste recycling and a product must be safe when used according to instructions for use. Therefore productisation of ashes will probably not reduce existing environmental criteria for earth construction. Productisation does not remove the need for quality control either. If ash material, that fulfils the product requirements and has adequate technical properties, can be produced with reasonable costs the productisation can improve the position of ashes on the market. Increase in landfill costs would make the refining more profitable and would support recycling that way. Utilisation of ashes in earth construction is not the only opportunity. It could be possible to find more profitable ways to utilize portion of ashes other than earth construction.

The complete report can be downloaded under vtt.fi.

Quelle: Technical Research Centre of Finland (VTT)

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