1 Recycling Large-Scale 3D Printed Polymer Composite Precast Concrete Forms Katie M. Schweizer, University of Maine, USA, katie.schweizer@maine.edu Sunil Bhandari, University of Maine, USA, sunil.bhandari@maine.edu Roberto A. Lopez-Anido, University of Maine, USA, rla@maine.edu Lu Wang, University of Maine, USA, lu.wang@maine.edu ABSTRACT Large-scale thermoplastic extrusion-based 3D printing, also referred to as additive manufacturing (AM), has shown promise for a multitude of applications in civil infrastructure. Advancements in this technology have led to increased usage and a subsequent increase in generated waste. Recently, the opportunity to recycle this material has contributed to lessening this waste. Presented in this work are established baseline thermo-mechanical and physical properties of carbon fiber – acrylonitrile butadiene styrene (CF-ABS) and wood flour – amorphous poly lactic acid (WF-aPLA). Additionally, this work is to be used in comparison with subsequent recycling cycles in evaluation of the mechanical recycling process for large-scale 3D printed CF-ABS and WF-aPLA with intended applications as formwork for precast concrete. KEYWORDS Large-scale 3D printing; Recyclability; Thermoplastic Composites; Precast Concrete Formwork; Additive Manufacturing INTRODUCTION Large-scale, thermoplastic composite, extrusion-based 3D printing or AM has been applied in infrastructure applications. Recent construction applications that have been demonstrated are: • Outlet diffuser for highway culvert rehabilitation (Bhandari et al., 2021); • Precast concrete formwork for a parking garage structure (Bhandari et al., 2022); • BioHome3D, which is a 56 m 2 modular house manufactured using a bio-polymer filled with wood fiber, which is recyclable (Ferrini-Mundi and Varahramyan, 2023). One significant use of large-scale 3D printing has been to make forms for precast concrete parts. The use of large-scale 3D printing as a method of formwork manufacturing provides geometric freedom for design while utilizing traditional concrete casting techniques. Alongside this, the use of large-scale 3D printing offers the added benefit of being an automated manufacturing process, which in turn reduces labor costs. Despite these advantages, printing large-scale parts produces tonnes of waste annually (Mikula et al., 2020). Landfill waste is a large contributor to global pollution and climate change, since they release large amounts of greenhouse gases into the atmosphere (Lou et. al., 2009). The introduction of additional solid waste streams, such as 3D printed waste material, not only will contribute to global pollution but also will contribute to the increased need for landfills. The 3D printed formworks discarded after casting concrete will perpetuate the amount of pollution entering the atmosphere. Recycling 3D printed formworks manufactured using thermoplastic composite materials can help mitigate the problem and needs to be further investigated for technical and economic viability. There are three commonly used methods for the recycling of thermoplastic composite materials: chemical, mechanical, and thermal recycling. Both chemical and thermal recycling are methods of fiber reinforcement recovery. Therefore, the matrix material is mostly wasted and does not contribute to the circular economy of the composite. Mechanical recycling is a method that recycles both the composite matrix and fiber reinforcements. Table 1 provides a summary of the advantages and disadvantages of the three recycling techniques (Baek et al., 2018; Pietroluongo et al., 2020).