Recycling Large-Format 3D Printed Polymer Composite Formworks Used for Casting Precast Concrete – Technical Feasibility and Challenges

Abstract

The use of large-format three-dimensional (3D) printed thermoplastic composites as formworks for precast concrete structures has emerged as a cost-effective solution addressing challenges related to skilled labor shortages and enabling design optimization. This research work investigates the technical feasibility of recycling large-format 3D printed polymer composite formworks. Thermomechanical recycling of 3D printed formworks was implemented and the recycled polymer composite feedstock was used to 3D print new formworks. Two commonly used short-fiber reinforced polymer composite materials were evaluated: one petroleum-based material, carbon fiber–filled acrylonitrile butadiene styrene (CF-ABS), and one biobased material, wood flour–filled amorphous polylactic acid (WF-aPLA). Mechanical properties of 3D printed specimens were characterized to evaluate their suitability as 3D printed formworks. Physical and thermal characterization methods were used to understand the change in thermal and mechanical properties of the thermoplastic polymers due to the recycling process. The study also employed similar methods to assess the potential contamination of polymer composites with cementitious materials. Results revealed that high-pressure water washing was effective in removing cementitious material from the formwork surface, and the recycled material did not show significant contamination. Thermomechanical recycling was shown to reduce the fiber length of reinforcing fibers and the molecular weight of the polymer material. The reduction in fiber length and the molecular weight of the material results in the reduction of material viscosity. The observed reductions in viscosity have the potential to limit the number of recycling iterations. However, thermal stability was maintained throughout all processing levels. In addition, the mechanical performance of the WF-aPLA material system was observed to increase after the recycling process. However, the mechanical performance of the CF-ABS material system was observed to decrease after recycling. Recycled 3D printed formworks were found to work effectively, albeit some reduction in mechanical properties of recycled formworks was observed. Large-format three-dimensional (3D) printed polymer composite formworks have been used to cast precast concrete structures. Currently, the formworks are disposed of in a landfill, once they have been used to cast the necessary number of precast concrete parts. If the 3D printed formworks could be recycled to make new formworks, the material cost of 3D printed thermoplastic composites could be significantly reduced while also making 3D printed formworks environmentally friendly. This research assesses the viability of thermomechanical recycling and reusing 3D printed thermoplastic composite formworks. The changes in material properties of thermomechanically recycled composites were studied. The effectiveness of cleaning the formwork using high-pressure water wash was investigated and the efficacy of using recycled 3D printed thermoplastic formwork was evaluated. The steps involved in manufacturing large format 3D printed formwork and recycling are described, and the challenges in each of these steps are discussed.