Modification of plastic waste using ultrafine fly ash for plastic mortars with enhanced strength and ductility

A simple and effective method to enhance waste plastics for use in performance-improved plastic mortars is presented. Waste polyethylene (WPE) was coated with hot ultrafine fly ash (UFA) through a welding process, converting its smooth, hydrophobic and unreactive surface into a rough, hydrophilic and reactive one. This modification improved the compatibility of WPE with surrounding cement paste. Mortars containing UFA-coated WPE achieved 26–31% higher compressive strength than those with unmodified WPE. Pore structure analysis indicated that by coating WPE with UFA, the air-entraining problem of WPE was overcome and the pore structure of the prepared mortar was densified with fewer air voids, owing to abundant hydration products deposited at the interface of the WPE. Moreover, the enhanced interface of the WPE with the surrounding paste enabled the transfer of stress from paste to WPE without large deformation of the paste. In this way, the ductility of mortars with UFA-coated WPE was enhanced. with larger peak strains and smaller elastic moduli. Additionally, as the use of hot UFA was a simulation of freshly discharged fly ash from combustion systems in power plants, the proposed technology would require no additional energy when applied in practice.