Environmental and geotechnical properties of lightweight aggregates made of reused solid wastes

Abstract

This paper presents the environmental and geotechnical characterisation of new synthetic lightweight aggregates (SLAs) composed of reused biomass fly ash and waste plastics, namely high-density and low-density polyethylene (HDPE and LDPE), with a 50:50 fly ash-to-plastic ratio by weight. One-dimensional compressibility, creep properties, compaction features and stress-strain-strength behavior of SLAs were evaluated together with hydraulic conductivity and water absorbability. The fly ash–HDPE aggregate was found to be less compressible upon loading than the companion material made of fly ash and LDPE and similar to traditional natural lightweight expanded clay aggregate. The values of creep coefficient (C αε) were slightly higher than those expected for dense sands, but comparable, or even lower, than those measured for other recycled materials. Peak friction angle (ϕ′) and cohesion intercept (c′), determined by triaxial compression tests, were in the ranges 42.3–46.3° and 1.3–8.6 kPa, respectively with the highest values concerning the fly ash–HDPE aggregate. The hydraulic conductivity (k) was around 3 × 10−4–4 × 10−4 m/s, highlighting favorable permeability properties of both aggregates. Leaching tests and thermal stability analyses proved the sustainability of both aggregates from an environmental point of view. The results obtained in the present study demonstrate the suitability of the investigated aggregates for many geotechnical applications.