Carbon nanotube polymer nanocomposites coated aggregate enabled highly conductive concrete for structural health monitoring

Recently, we proposed a new strategy to develop a three-dimensional conductive network within a cement mortar by coating sand with graphene. In such a design, the interfacial transition zone (ITZ) was directly embedded in the conductive network, thus resulting in high piezoresistive performance. Considering that the ITZ between coarse aggregate and paste is typically much more vulnerable than that of the ITZ between fine aggregate and paste, here we extend this strategy to concrete, whose piezoresistive property has been rarely reported yet intimately relevant for practical application. Conductive fine and coarse aggregates are readily prepared by dipping coating with carbon nanotube (CNT) polymer slurry. Because of the high volume percentage of aggregates (∼70%) in concrete, the obtained concrete exhibit very high conductivity at low CNT usage of 0.41% (by weight of cement), several orders of magnitude higher than that reported before at similar CNT load. We find that the mixture incorporating conductive aggregates has a 28-day electrical resistivity of 1076 Ω cm with a compressive strength loss of 17.8%. On this basis, we further optimize the high-conductivity concrete by connecting conductive aggregates with a small amount of 0.25 wt% carbon fibre, which demonstrates an outstanding 28-day electrical resistivity of 235 Ω cm and an excellent fractional change in resistivity of ∼80%, more than one order of magnitude higher than those obtained in comparable systems. The experimental results also testify that our smart concrete exhibits acceptable mechanical properties and durability. The simple operation and low-cost benefits make our smart concrete demonstrate great potential for large-scale practical application.