Plasticizers as Dispersants for Carbon Nanotubes in Self-sensing Cement Composites

Carbon nanotubes (CNT) modify not only the mechanical but also the electrical properties of the cement matrix, allowing the development of self-sensing cement composites (SSCC). These composites can sense their own deformation through changes in their electrical resistivity, acting as strain sensors, increasing the operational safety of concrete structures by indicating preventive or corrective maintenance. The efficiency of SSCC depends on the electrical properties of the conductive filler and its dispersion degree throughout the matrix. The most commonly employed method of ensuring adequate dispersion of CNT is using chemical dispersing agents. This work aims to compare the effectiveness of two types of plasticizers as dispersing agents for CNT, identifying how they affect the self-sensing capacity of SSCC. CNT contents of 0.10 and 0.20%, by mass of cement, were blended in a cement matrix using two types of commercial superplasticizers as dispersant agents, one naphthalene based and one polycarboxylate ether based. SSCC cement pastes were cast in 50 mm cubic molds with four copper embedded electrodes and cured for 30 days in a humid environment. After curing, an electrical potential was applied through the electrodes and the electrical resistivity of the SSCC was acquired during successive compressive load applications. A 10 V DC power supply was used for this purpose. The changes in electrical resistivity of each cube were correlated with deformations measured by LVDT. Results showed that both the type of superplasticizer used and the CNT content affect the piezoresistive response of SSCC. Naphthalene-based superplasticizer presented better performance as dispersing agent and led to SSCC with better self-sensing response. Results indicated that the chemical basis of the dispersing agent for CNT has great influence on the fabrication of efficient SSCC.