Measurement techniques for self-sensing cementitious composites under flexure

Abstract

Intrinsic self-sensing concrete has gained substantial interest recently as a promising construction material for smart structures. Most of the research focuses on testing their sensing behaviour under pure compression, but in practice, damage to concrete structures due to bending is more commonly seen. It is thus necessary to also test the sensing performance of the composites under flexural loading. Due to the variation of the stress distribution in a concrete element subject to bending, the influence of the geometry of electrodes on measured results is more complex. This study investigated the self-sensing behaviour of prismatic graphite-cementitious specimens under three- and four-point bending with different electrode placements. Composites were tested both in the elastic and plastic range by applying cyclic and monotonic flexural loading. Prisms with different sample depth, sample width, electrode penetration and electrode diameter were further modelled numerically using Finite Element Analysis (FEA) to study the electrical behaviour. Experimental results show that to obtain accurate measurements for composites under flexure, the electrodes need to be at close spacings with shallow penetration at the tensile side of the specimen in order to measure behaviour in the tensile zone. An equation for the relationship between the measured resistance and the geometry variables has been found through numerical simulation that can estimate the influence zone within the sample and hence enable optimisation of the electrode placement for self-sensing cementitious composites under flexure.