Avaliação das propriedades eletromecânicas de compósitos cimentícios à base de MWCNTs, CFs e EPS para aplicação em sensoriamento

Abstract

Concrete structures are widely used due to their durability, but they are subject to degradation, which compromises their integrity. In this context, self-sensing cementitious composites, obtained through the incorporation of electrically conductive additions such as carbon fibers (CFs) and carbon nanotubes (CNTs), emerge as an alternative for structural monitoring due to their piezoresistive properties. In light of this, the present study aimed to develop lightweight self-sensing cementitious composites based on multi-walled carbon nanotubes (MWCNTs), CFs, and expanded polystyrene (EPS) for sensing applications. To evaluate the behavior of the produced mortars, tests were carried out for workability, water absorption, void index, and density, ultrasonic pulse velocity, compressive strength, and electromechanical performance. Initially, a pilot study was conducted to investigate the isolated effects of different concentrations of CFs (0.10%, 0.20%, 0.50%, and 1.00%) and EPS (20% and 30%), in addition to the incorporation of 0.2% MWCNTs. Mortars produced with MWCNTs showed good electromechanical results but exhibited an 8.95% reduction in compressive strength, indicating agglomeration. Among the mortars with CFs, the 0.1% content showed the best results, with a compressive strength of 55.58 MPa and a favorable electromechanical response. For EPS, the 30% content caused a significant reduction in compressive strength of 51.30%, while the other parameters remained close to those observed for the 20% content. Based on the mixtures that presented the best compressive strength and piezoresistive behavior in the pilot study, the optimal contents for multicomponent composites were defined (20% EPS, 0.1% CFs, and 0.2% MWCNTs), leading to the production of combinations such as EPS + MWCNTs, EPS + CFs, and EPS + MWCNTs + CFs. Among the multicomponent mortars, the EPS + CFs combination showed the best performance, with the most standardized electromechanical response, a compressive strength of 37.68 MPa, and lower electrical resistivity compared to mortars with a single addition. In general, with the replacement of fine aggregate by EPS, no significant variations in resistivity were observed in response to cyclic loading, indicating that the greater deformations typical of EPS-based composites, although they may promote closer contact between carbonaceous additions, do not necessarily increase the sensitivity of the resulting composite.