Micromechanics modeling of the uniaxial strain-sensing property of carbon nanotube cement-matrix composites for SHM applications

Recent advances in the field of Nanotechnology have made possible the development of new smart materials, among which Carbon NanoTube (CNT) cement-based composites are attracting an increasing attention. These composites exhibit strain-sensing capabilities providing measurable variations of their electrical properties under applied mechanical deformations. This unique property, together with the similarity between these composites and structural concrete, suggests the possibility of developing distributed strain-sensing systems with substantial improvements in the cost-effectiveness of large-scale concrete structures. In order to design and optimize self-sensing CNT-based composites, it is therefore essential to develop theoretical models capable of simulating the relationship between external mechanical strains and the effective electrical conductivity. This paper presents a micromechanics model to predict the piezoresistive properties of CNT cement-based nanocomposites, with the consideration of waviness and non-uniform distributions of nanoinclusions. The origin of the piezoresistive response is attributed to (i) strain-induced changes in the volume fraction, (ii) filler reorientation and, (iii) changes in the tunneling resistance. In order to count on an experimental basis to use as benchmark for validation, several nanocomposite cement-based specimens are manufactured and tested under uniaxial compression.