Electromechanical Testing of Smart Lime Mortars for Structural Health Monitoring

Masonry structures are characterised by low tensile strength and limited ductility. Excessive static or high-cyclic loading or seismic excitation can lead to large localised strains and cracking. It is therefore essential to monitor the response of masonry structures to external loading, especially in the case of historic buildings and infrastructure. The present work aims at designing novel smart intervention materials for multifunctional application in historic masonry structures as a means of SHM, simultaneously structurally and chemically compatible with the in-situ material. The materials investigated consist of lime mortars mixed with different conductive micro- and nanofillers dispersed in the binder. Smartness stems from the materials' enhanced piezoresistivity, namely the constitutive relation between strain and electrical resistivity. Through application as a repointing agent in existing structures, these materials can be used as deformation and damage sensors. Electromechanical testing employing cyclic compression was conducted on mortars with different doping levels of three conductive fillers: graphite powder, carbon nanotubes and carbon microfibres. The electromechanical study involved the determination of the piezoresistive gauge factors of the different mixes for determining the optimal doping level for each employed filler. The mortars were evaluated in terms of piezoresistive sensitivity and structural application scalability.