3D-printed recycled plastic eco-aggregate (Resin8) concrete

Plastic waste is a global environmental issue, while natural resources, such as sand, is limited and are depleting as opposed to the abundance of waste plastics. This study investigates the suitability of adding recycled plastic waste, in the form of Resin8, for the first time, into 3D printed concrete (3DPC) as fine aggregate replacement. Replacement values of 5 %, 10 % and 15 % of natural sand by volume are investigated, which are further characterised by varying Resin8 particle sizes. Particle sizes of Resin8 included are sub-5 mm, sub-1 mm and a combination of the two at equal proportions (50/50). The Resin8 replacement mixes are tested against the standard ‘reference’ 3DPC mix of Stellenbosch University. A total of ten mixes were formulated, which were 3D printed and cast, to investigate the effect of Resin8 on the printed samples process. The fresh and hardened properties of each mix were investigated, which included slump flow, rheological characterisation, density and air content, buildability, and flexural and compressive strength in two orientations due to the anisotropic nature of 3DPC. Further, the microstructure of samples was investigated using micro-computed tomography and scanning electron microscopy analyses. The addition of Resin8 led to more flowable mixes with less thixotropic behaviour, which decreased the buildability performance. The flexural and compressive strength decreased as the amount of Resin8 increased, while an improved interlayer bond strength was found with the addition of Resin8. An overall performance loss was found by adding Resin8 into 3DPC mixes. However, replacing a portion of fine aggregates in 3D printable concrete with Resin8 is a viable solution that can effectively reduce plastic waste in our environment. Even small amounts of Resin8 replacement can make a significant impact, considering concrete is the most widely used construction material.