Experimental Characterization of Smart Cementitious Composites Reinforced with Multi-Walled Carbon Nanotubes for the Health Monitoring of Infrastructures

The development of smart cementitious composites reinforced with Multi-Walled Carbon Nanotubes (MWCNTs) for Structural Health Monitoring (SHM) applications still represents a significant challenge, mainly due to diffi- culties associated with achieving stable and homogeneous nanotube dispersion within cementitious matrices. In this study, MWCNT-reinforced cement paste composites containing different nanotube concentrations (0.00–1.50 wt%) were produced through ultrasonication treatment combined with the use of a commercially available naphthalene-based superplasticizer as dispersing agent. The additive, commonly used to improve the workability of cementitious materials, was also exploited here for the dispersion of MWCNTs, thereby assuming a dual functional role. The influence of MWCNT incorporation on the mechanical, electrical, piezoresistive and mi- crostructural behavior of the composites was experimentally investigated. The results show that the MWCNT- based cementitious composites exhibit a pronounced piezoresistive response strongly dependent on nanotube concentration. Under cyclic loading conditions, the composite containing 0.40 wt% MWCNTs exhibited the high- est sensing performance, reaching a gauge factor of 310 together with good linearity (22.97%), repeatability (14.57%) and hysteresis (29.11%), exceeding values commonly reported in recent literature for cementitious composites incorporating conventional dispersing agents. SEM analyses highlighted the formation of more ho- mogeneous and interconnected conductive regions for MWCNT contents between 0.40 and 0.75 wt%, while TG- DTG and XRD analyses confirmed that MWCNT incorporation did not significantly alter the main thermal decom- position mechanisms or phase composition of the cementitious matrix. The experimental results were also com- pared with the predictions of a micromechanical model accounting for MWCNT agglomeration, segregation, cur- vature and electron transport mechanisms, showing good agreement with the observed experimental trends. The results obtained provide useful insights into the correlation between nanotube dispersion, conductive network evolution and piezoresistive response, contributing to the design and optimization of high-performance self-sensing cementitious composites.