Potential of compost mixed with tuff and pozzolana in site restoration

The present research is aimed at evaluating the potential of mixtures made of different percentages of compost (10%, 20% and 30% by volume) and inorganic waste from extraction activities (tuff and pozzolana) for site restorations. The materials alone and the mixtures were characterised from a geotechnical point of view, in order to determine the optimal percentage to be used. In particular, the oedometric test and the direct shear test were performed. Also the environmental quality of the materials was investigated through chemical characterisation and a leaching test. In addition, a lab-scale seeding test was carried out to assess the potential phytotoxicity of the mixture. Finally, at the end of the experimentation the accumulation of heavy metals in the plants was determined and the plants+artificial soil system underwent a shear stress test. The presence of compost in the percentages tested did not reduce the mechanical performances of the inorganic residues, guaranteeing good resistance and stability. In fact, the response to oedometric compression, the compression coefficient and the internal friction angle of the mixtures were quite similar to those obtained for tuff and pozzolana alone. The mixtures selected as optimal from a mechanical point of view (30% by volume of compost and 70% by volume of tuff/pozzolana), did not represent a potential hazard for the environment due to the low content and negligible leachability of heavy metals. In addition, such mixtures can provide a good substrate for revegetation thanks to the high content of organic matter and the absence of phytotoxic effects in the conditions tested.