Interpreting and modelling the high piezoresistive sensing performance of cementitious materials

Self-sensing cementitious materials are set to play a crucial part in structural health monitoring operations on buildings and infrastructure due to the ubiquitous presence of cement-based materials in the built environment, their ease of modification for enhanced sensing capabilities and the low cost of application. It is therefore of prime importance to fundamentally understand the physical mechanisms behind their self-sensing performance. One of the salient characteristics of cementitious materials is their notably high piezoresistive sensitivity under compression, reaching an order of magnitude above what would be expected from simple coupled electrical-mechanical analysis, even before modification with electrically conductive inclusions. While widely observed in the lab and tentatively attributed to various micro-or nano-scale material features and phenomena, this remarkable characteristic has not been sufficiently modelled and explained. This paper offers a micro-mechanical interpretation of the physical mechanisms behind the high piezoresistive gauge factor of cementitious materials. By accounting for the distortion of the shape of the different phases of the material, such as the paste, pores and aggregates, the resulting shifts in effective volume fractions as well as the closure of cracks perpendicularly oriented with respect to the load direction, the gauge factor of the material is able to reach the experimentally-derived values. The proposed model is used to evaluate the influence of various mechanical, electrical and loading parameters on the piezoresistive behaviour of cementitious materials, indicating potential future areas of focus for further experimental and numerical simulation work.