Improvement of the Self-Sensing Properties of the 3D Printing UHPC Incorporating Conductive Rubber (2026-03)¶

This study develops an extrusion-based 3D-printable ultra-high-performance concrete (UHPC) incorporating conductive rubber fillers to achieve reliable self-sensing. Five UHPC mixtures were designed with 0%, 10%, and 20% conductive rubber crumb or powder replacing the fine aggregate by volume, where each mix contained 1% straight short steel fibres. The piezoresistive behaviour under cyclic and monotonic compression was investigated for cast and 3D-printed specimens in the X/Y/Z directions under both AC and DC electric currents, and the self-sensing performance was assessed using the RSRS criteria. Under AC protocol, UHPC with 10–20% conductive rubber showed stable, repeatable and synchronized resistance response during both cyclic and monotonic loading, and a clear indication at brittle failure, where the rubber powder generally exhibited higher sensitivity than the rubber crumb. Under DC protocol, the self-sensing performance was inferior due to polarization effects and the cast specimens failed to provide valid sensing signal results as resistance increased beyond the instrument limit (100 MΩ), whereas printed specimens remained measurable and showed more stable FCR variations, particularly along the printing direction. CT results on CRC10 and CRC20 show a layered distribution of steel fibres in 3D-printed specimens and a random distribution of conductive rubber particles, which supports the observed differences in conductivity and directional sensing behaviour. These findings demonstrate the feasibility of integrating self-sensing performance into 3D-printed UHPC for smart and resilient infrastructure applications.