Piezoresistive and mechanical performance of nano-TiO₂-modified 3D-printed cementitious composites

The integration of self-sensing functionality into 3D-printed cementitious materials presents a promising pathway toward intelligent infrastructure capable of real-time structural health monitoring. This study investigates the influence of nano-titanium dioxide (nano-TiO₂, NT) on the mechanical, electrical, and piezoresistive behaviour of both mould-cast and extrusion-based 3D-printed cementitious composites. NT was incorporated at 0-30% replacement levels (by binder weight) to evaluate its effects on flowability, compressive strength, flexural strength, electrical resistivity, and fractional change in resistivity (FCR) under cyclic compression. Results indicate that a 10% NT dosage provides the optimal balance between printability, strength enhancement, and piezoresistive sensitivity. Compressive strength increased by approximately 15% compared to the control mixture, while higher dosages (> 15%) resulted in strength degradation due to nanoparticle agglomeration and reduced fly ash contribution. Electrical resistivity decreased with increasing NT content up to 15%, indicating an enhanced ability of the cementitious matrix to support interconnected charge-transport pathways through reduced interparticle spacing, improved microstructural packing, and modified ionic conduction. The 3D-printing process further improved compressive strength (up to 34%) and piezoresistive response due to filament alignment and densification effects, although flexural strength decreased because of interlayer anisotropy. The findings demonstrate that NT can serve as a semi-conductive modifier in printable self-sensing cementitious systems, provided that dispersion and interlayer bonding are carefully controlled.