Physicochemical and geotechnical properties of an ash-slag mixture deposited on a landfill in terms of its use in engineering

Abstract

Coal combustion ash-slag mixtures have been deposited in landfills in Poland for decades. At the same time, there is a shortfall in the amount of available materials related to the construction and modernisation of transportation infrastructure. Thus, a typical landfill of a power station was chosen and the aim of the study was to assess the suitability of an ash-slag landfill mixture for construction engineering purposes. The following physicochemical analyses were conducted: pH, specific electrical conductivity and determination of the leachability of basic (Ca, Na, K and Mg) and trace elements (Cd, Pb, Cr, Zn and Cu). The content of selected basic and trace elements were determined in the eluates by FAAS and standard methods were applied for geotechnical analyses. The most likely conditions were assumed to the model. The mixture will not jeopardize surface water quality in terms of the concentrations of basic, hazardous or priority elements. The content of these elements also does not exceed permissible concentrations for groundwater. The conductance and pH of the eluates are in compliance with current laws. The solid mixture has favourable geotechnical parameters which are significantly dependent on moisture content. The slope stability calculations for embankments created from the mixture at optimum moisture content and high compaction (I S ≥ 0.95) indicate that they will be stable even in the case of high gradients (1:1.5). The slopes will be unstable in conditions of submersion, which should not occur if we assume the embankment will be used for passive flood protection. The mixture is particularly suitable for the purposes of earth structures, provided that they are isolated from water.

Measurements of the Permeability Coefficient of Waste Coal Ash under Hydrostatic Pressure to Identify the Feasibility of Its Use in Construction

“…Research by Reddy et al [32] showed that the permeability coefficient of the power plant bottom ash had values similar to those obtained in this study from 1.34 × 10 −6 to 2.01 × 10 −6 m/s; hence, such waste ash can be effectively used as road embankment construction material. In contrast, Szwalec et al [18] give a wide range of permeability coefficient values for coal waste ash ranging from 3.4 × 10 −11 to 2.61 × 10 −2 m/s. Low water permeability coefficients (from 1.16 × 10 −5 to 1.27 × 10 −5 m/s) obtained by Lange et al [19] were explained by the chemical composition of the bottom ashes and slags containing large amounts of The average values of permeability k ranged from 4.4 × 10 −7 to 1.91 × 10 −6 m/s.…”

“…The permeability coefficient measurements were performed with a constant hydraulic gradient as well as with a constant flow [30]. The tests consisted of determining the amount of water that will filter through a soil sample with a cross-section A in time t at the hydraulic gradient i and at the determined water temperature [10,[17][18][19][20][21][22][23][24][25][26][27][28][29]. The hydraulic gradient i was calculated according to the following formula [30]:…”

“…Research on the assessment of the permeability coefficient of waste coal ash is limited [17][18][19][20]. The water permeability of coal ash and slag was studied in the work of Lange et al in order to assess the possibility of their use as road surface layers [19].…”

An assessment of the impact of the degree of the filling of shallow voids on the possibility

“…One of the evaluation methods is the analysis of the aqueous extract obtained in the leaching test. Research into energy waste has shown that the content of heavy metal cations in aqueous extracts is low, which proves that they create forms that are insoluble or sparingly soluble in water (Mazurkiewicz 1990;Mazurkiewicz et al 1997;kapuściński and Strzałkowska 2005;Szwalec et al 2017). However, it should be noted that the standard aqueous extract completely ignores the issues of waste kinetics.…”

“…However, it should be noted that the standard aqueous extract completely ignores the issues of waste kinetics. Some waste releases toxic substances only after some time or under specific conditions (kapuściński and Strzałkowska 2005;Szwalec et al 2017;Dudas 1981). An important role in the leaching of fly ash is played by the way in which a given element is present in coal (Izquierdo and Querol 2012).…”