Piezoresistive Properties of Natural Hydraulic Lime Binary Pastes with Incorporated Carbon-Based Nanomaterials under Cyclic Compressive Loadings

Abstract

Natural Hydraulic Limes (NHL) are extensively used for the restoration of Monuments of Cultural Heritage, often combined with pozzolanic materials, such as natural pozzolans and metakaolin etc. In the present study, five (5) different cases of binary lime-based pastes composed of a specific type of NHL (NHL5) and metakaolin as pozzolanic addition were examined, that were reinforced with carbon nanostructures, namely graphene and carbon nanotubes. For the first time in restoration mortars, the incorporation of carbon nanostructures was investigated, aiming to produce materials with adequate piezoresistive response, so that they have the potential to be exploited for in situ structural health monitoring. The compressive strength, flexural strength, electrical resistance and piezoresistive response of the composite pastes was examined. The results showed that all modified carbon nanostructures lead to a significant reduction in electrical resistance. The pastes reinforced with 2D nanostructures (graphene family) displayed up to 30% increase in compressive strength and the pastes reinforced with 1D nanostructures (carbon nanotubes) displayed enhanced flexural strength (up to 100% increase). Piezoresistivity was attained for almost all investigated pastes, nevertheless the graphene oxide (GO) was considered as optimal reinforcement as the sensing ability of such pastes was found to be almost proportional to the applied compressive load level.

Present Status and Perspectives of Graphene and Graphene‐related Materials in Cultural Heritage

“…[153,155] Further work from Dimou et al showed no significant changes in the flexural strength due to the addition of GO, but an improvement in the compressive strength, which was reported to increase by 20-30% compared with the reference mortar. [156][157][158] Besides investigating these properties, Dorin et al proved that GO addition only slightly improves the adhesion of the modified mortar. In these studies on the influence of GO on the performance of natural hydraulic mortars, different concentrations of GO in different physical forms (aqueous dispersions or powder) have been tested.…”

“…[224] Beyond these applications as external sensors, GRMs could also be used as a sensing system within complex matrices such as cementitious materials. [225] A seminal work from Dimou et al [156] proposed a binary paste matrix (natural hydraulic lime and metakaolin) modified with rGO as reinforcement for the development of cultural heritage restoration mortars. The addition of rGO provokes a decrease in electrical resistance that indicates a good distribution of the electrically conductive nanomaterials within the binder, forming an efficient electrical network.…”

“…showed no significant changes in the flexural strength due to the addition of GO, but an improvement in the compressive strength, which was reported to increase by 20–30% compared with the reference mortar. [ 156–158 ] Besides investigating these properties, Dorin et al. proved that GO addition only slightly improves the adhesion of the modified mortar.…”