Graphite-polydimethylsiloxane composite strain sensors for in-situ structural health monitoring

Here we describe the synthesis and testing of miniature sensors for structural health monitoring. The sensors were incorporated into building materials to detect strain relaxation events within the region of elastic deformation prior to the onset of plastic deformation. Our sensors consisted of thin composite films of polydimethylsiloxane and graphite nanoparticles that conduct via tunnelling percolation. Tunnelling-percolation through elastomers with low Young's modulus is highly sensitive to deformation and gives a large piezoresistance which we use to infer the local strain. The response of sensors embedded in calcium aluminate mortar, Portland cement mortar, and very fine sand columns was compared under stress. We show that the sensors can detect micro-events where strain is redistributed locally from one direction to another and may thus be used to monitor structural integrity and provide early warning of material disaggregation.