Evaluation of Continuous Epoxy-Impregnated Carbon Fiber Reinforcement in a 3D-Printable Geopolymer Composite (2025-12)¶

This study investigates the potential of geopolymer reinforcement for extrusionbased 3D printing using in-situ impregnation of continuous carbon fibre. The geopolymer is composed of fly ash, ground granulated blast furnace slag and an activator, specifically developed for 3D printing. Although 3DCP has seen significant advancements in recent years, structural reinforcement remains a largely unresolved challenge. In conventional concrete construction, steel reinforcement is used to withstand tensile forces that cannot be absorbed by the mineral building material alone, creating the composite material reinforced concrete. For additive manufacturing to remain competitive, printed concrete must offer comparable quality and performance, without compromising the benefits of geometric freedom, digital design, and automation. The use of continuous carbon fibre strands with a functional epoxy resin infiltration enables strong adhesion between the fibre and the geopolymer matrix, allowing for layer-wise reinforcement in tensile zones. Moreover, clinker-free geopolymers activated by highly alkaline solutions offer a more sustainable alternative by significantly reducing CO₂ emissions. Various combinations of geopolymer matrix and carbon fibre reinforcement are evaluated through three-point bending tests to determine flexural tensile strength, and through pull-out tests to assess peak load. Microscopic investigations using light microscopy and scanning electron microscopy (SEM) are conducted to analyse the interfacial bonding between fibre, geopolymer, and epoxy resin. The results demonstrate that embedding impregnated fibres "fresh-infresh" provides the most effective fibre–mortar bond, without limiting shape flexibility during printing.