Acoustic Emission Analysis of Tensile Failure in Layered 3D-Printed Fibre-Reinforced Fine-Grained Concrete

This study investigates the cross-layer tensile fracture of layered 3D-printed fine-grained concrete using acoustic emission (AE) monitoring. Direct tensile tests were performed on various layer configurations (monolithic, layered, and pyramidal) with and without polypropylene fibre reinforcement. AE descriptors (RMS and ring count) were evaluated on a normalised time-to-failure axis. All configurations exhibited a low baseline AE level over most of the loading history, followed by a pronounced late-stage increase as failure approached. The layer architecture primarily governed the temporal characteristics of the pre-failure activity: multilayer specimens, especially those with five layers, showed more intermittent burst sequences than monolithic specimens, which remained comparatively quiet until terminal instability. Fibre reinforcement increased late-stage intermittency and dispersion, consistent with additional mechanism-rich activity near failure, whereas pyramidal stacking without fibres tended to exhibit comparatively low detectable pre-failure AE activity until the final stage. Cross-configuration integrals highlighted configuration-dependent differences in accumulated IRC values (notably elevated in three layers without fibres), confirming that energy-type and count-type AE metrics are complementary rather than interchangeable.