Investigation of 3D Printed Self-Sensing UHPC Composites Using Graphite and Hybrid Carbon Microfibers

Area of Science:

• Materials Science
• Civil Engineering
• Nanotechnology

Background:

• Ultra-High Performance Concrete (UHPC) offers superior mechanical properties.
• Developing self-sensing concrete is crucial for structural health monitoring.
• 3D printing enables complex concrete structure fabrication.

Purpose of the Study:

• To develop 3D-printable, self-sensing UHPC with enhanced piezoresistive properties.
• To investigate the effects of graphite (G), milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) on UHPC.
• To optimize filler content for mechanical performance and sensing capabilities.

Main Methods:

• Incorporation of G powder, MCMF, and CCMF into UHPC matrix.
• Percolation curve analysis to determine optimal filler concentrations.
• Quasi-static cyclic, dynamic cyclic, and monotonic compressive loading tests.
• Evaluation of piezoresistive and mechanical properties of 29 mix designs.

Main Results:

• Graphite improved conductivity but reduced strength; MCMF/CCMF enhanced compressive strength (up to 19.2%) and Young's modulus (up to 9.8%).
• Hybrid MCMF/CCMF combinations significantly improved sensing performance with strain linearity over 600 με.
• Optimal mix (3G250M250CCMF) achieved a strain gauge factor of 540, resolution of 68 με, and accuracy of 4.5 με.
• 3D-printed specimens showed slightly reduced performance compared to mold-cast.

Conclusions:

• Milled and chopped carbon microfibers are effective in enhancing both mechanical and sensing properties of UHPC.
• The developed self-sensing UHPC is suitable for 3D printing applications in structural health monitoring.
• Further research may focus on mitigating performance reduction in 3D-printed specimens.