Geotechnical and chemical characteristics of ash and slag mixture of Skawina Power Plant (Poland)

Abstract

Fuel ashes are mainly utilised in civil engineering and earth structures, road engineering in particular. Tests have also been performed to evaluate them for hydraulic engineering purposes, e. g. for sealing coarse-grained materials. However, there is a high risk of exposing proximal ecosystems to emission of substances, such as heavy and alkaline metals contained in the fly ashes and the ash-slag mixtures. The wastes may also cause water mineralization, soil salinification of water and soil alkalisation as well as secondary air pollution with dust. The research described in the paper aims at determination of basic geotechnical characteristics of the ash-slag mixture taken from the dumping site of the Skawina Power Station that has a potential for earth engineering. Moreover, there was determined the leachability of basic (Ca, Na, K, Mg) and trace (Cd, Pb, Cr, Zn, Cu) elements that could negatively influence the ecosystems in the adjacent areas. The obtained results of the geotechnical tests of the ash-slag mixture suggest a high potential for earthworks. The requirements of the relevant standards concerning utilising fuel ashes are met; only frost-heave of the mixture is questionable. Assuming that the soil will be used for the embankment construction, i. e. above the ground water surface, the above mentioned standard requirements should not matter. The analysis of the basic and trace elements contents as well as pH value and conductance also confirms the high potential of this material for the construction sites. The tests of leachability show that the effluent coming into existence as a result of soaking or filtration through the tested mixture should not negatively influence the ecosystems surrounding the site. There may be some doubts in this research area related to leached potassium which could pollute groundwater (water quality classes IV or V). However, assuming that the above mentioned technical requirements (Standard: PN-S-02205:1998) are met, i. e. the mixture will be placed without direct contact with groundwater and the first “biological barrier” which adopts potassium is the surface water, the tested material should be considered as suitable for building earth structures.