Estudo do potencial piezoresistivo de argamassas de cal e metacaulim utilizando o pó de grafite

Abstract

Lime has been widely used as a construction material since ancient times across the world. Currently, lime- and pozzolan-based materials are frequently employed in the repair of historical structures. In recent years, research has emphasized the importance of continuous monitoring of ancient buildings to assess structural health. In this context, the incorporation of conductive fillers, such as carbon fibers or nanotubes, graphite, carbon black, or graphene oxide, has enabled the development of concrete with self-sensing capabilities. By means of electrical resistivity measurements, it becomes possible to monitor the material's integrity, allowing for the detection of damage and crack formation. Furthermore, these composites often exhibit piezoresistive behavior, a property that correlates variations in electrical resistivity with their state of stress and strain. However, these materials are not fully compatible with heritage structures, and studies on restoration lime mortars reinforced with piezoresistive materials remain in an early stage, with several knowledge gaps still to be addressed. The present work aims to investigate lime–pozzolan mortars incorporating graphite powder with respect to their piezoresistive properties for application in historical constructions. Lime–metakaolin pastes were produced with graphite powder contents of 0%, 1%, 5%, and 10% to evaluate physical, mechanical, and piezoresistive properties. Based on the results, the compositions that exhibited the most promising piezoresistive behavior were identified. Among these, mixtures containing 70% and 80% lime were selected for mortar production with a binder-to-sand ratio of 1:3 by mass. Subsequently, mechanical and electrical resistivity tests were carried out. The results revealed a relationship between density and electrical resistivity, with resistivity increasing as moisture content decreased. Regarding compressive strength, higher metakaolin content led to improved mechanical performance. In terms of piezoresistive behavior, mortars with graphite powder additions demonstrated promising performance, exhibiting increasing linearity and sensitivity with higher applied stress levels. Overall, the findings indicate that incorporating graphite powder significantly enhances the piezoresistive properties of lime-based mortars while maintaining mechanical and chemical compatibility with historical structures, thus offering strong potential for applications in restoration and structural health monitoring.