Synthesis optimization of CNTs@glass beads core-shell material by microwave radiation and piezoresistive sensing performance of its reinforced cement-based composites

In this paper, carbon nanotubes (CNTs) were grown in situ on the surface of glass beads using a microwave radiation method, resulting in the synthesis of CNTs@glass beads core-shell material (CNTs@Gb). The properties of CNTs@Gb were optimized through a combination investigations of microscopic morphology, infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy and conductance measurements. Secondly, CNTs@Gb reinforced cement-matrix composites (CNTs@Gb/C) were prepared by incorporating the optimized CNTs@Gb into cement matrix, and their mechanical and electrical properties and piezoresistivity were systematically evaluated. The results show that when the ratio of microbeads to pyrrole is 3.3∶1, the well-coated polypyrrole (PPY)@Gb is obtained, the ratio of PPY@Gb to ferrocene is 1∶1.5, and the performance of CNTs@Gb is the best after 50 s microwave treatment. The 28 d flexural, compressive strength of CNTs@Gb/C at 2.5% CNTs@Gb mass dosage are increased by 10.3% and 6.8% compared with the blank group, and the direct current (DC) resistivity, alternating current (AC) resistivity at 100 Hz are decreased to 9.3 kΩ·cm, 5.89 kΩ·cm, which are 77% and 84% lower than that of the blank group, respectively. Under variable rate cyclic loading at rates of 1 kN/s, 2.5 kN/s, and 5 kN/s (0—15 MPa amplitude), the average resistivity rate can reach 76%, with the highest stress and strain sensitivity reaching 5.57%/MPa and 13.2%, respectively, which have excellent sensing performance. It is favors to develop CNTs@Gb/C as high-performance intrinsic sensors applied in structural health monitoring.