Sustainable cement mortar with recycled plastics enabled by the matrix-aggregate compatibility improvement

Abstract

Use of recycled waste plastics (RWPs) as the aggregates of concrete has attracted increasing attention for sustainable concrete manufacture with great environmental benefits. However, the replacement of natural aggregates by RWPs always results in degradation of mechanical properties due to poor aggregate-matrix compatibility, which greatly limits the uses of RWPs in practical concrete manufacture. In order to overcome this shortage, polymer (ethylene–vinyl acetate, EVA) coated RWPs, i.e. polypropylene (PP) and polyamide (PA), were investigated to tune the aggregate-matrix interactions in cement mortars. Density, strength and ductility were measured to assess the physical and mechanical properties of mortars with RWPs. Microstructure was qualitatively and quantitatively analyzed using scanning electron microscopy (SEM) with backscattered electron (BSE) mode and energy-dispersive X-ray spectroscopy (EDS). Results showed that single EVA addition into cement mortars kept the mortar density, decreased the compressive and flexural strengths, but increased the deformation and energy absorption to an extent of 100% in mortars with high EVA content. While the addition of RWPs witnessed a reduction in density of about 13–16%. The dual mix of 10% RWPs and 5% EVA mitigated the reduction trend in compressive strength and provided a slight increase (1.5%) in flexural strength compared with the mortars with single mix of 10% RWPs. The EVA addition built organic–inorganic interfacial transition zones (ITZs), improving the matrix-RWPs adhesion and coordinate their deformations. The mechanisms of compatibility improvement of EVA on RWP-cement mortar were proposed towards future design and fabrication of green concrete.