Abstract: Polymer 3D printing is popular due to its accessibility and low material waste. While commonly used in prototyping and medical applications, its potential for molds in complex concrete geometries, such as heritage reproductions or artificial reefs, remains underexplored. These applications require resistance to degradation from UV exposure, rain, and highly alkaline concrete (pH~13). This study evaluates the accelerated degradation of 3D-printed PLA specimens. Four PLA types were tested: virgin PLA extruded in the lab, commercial PLA, PLA with 50% metal powder, and PLA with encapsulated metal powder. Rectangular specimens were printed and tested under flexural loads following ISO-167 standards. Initially, their performance was assessed without exposure. Then, half of the specimens underwent UV and rain simulation, while the rest were immersed in an alkaline solution (pH 13, 50 ?C). Dimensional changes and flexural strength were measured at five intervals. Exposure to an alkaline medium at 50 ?C is more aggressive than UV radiation, limiting the lifespan of PLA formwork. Adding metal powder weakens PLA by 65% after 7 days, making it unsuitable. Printing defects accelerate degradation. Unmodified PLA is the best choice for concrete formwork, with commercial PLA and PLA from pellets showing nearly identical behavior.
