Elimination of polarization effect in DC measurement of resistivity of CNT-cement composites

Abstract

Multi-walled carbon nanotubes (CNT) may serve as electrically conducting fillers for traditional cement-based materials. Introducing small amount of CNT in the matrix of concrete turns the latter into a smart piezoresistive material applicable for the structural health monitoring of reinforced concrete structures. CNT–cement composites are subject to polarization during direct current (DC) resistance measurement. This phenomenon results in increase of electrical resistance of composites hindering their practical application. Suggestions for dealing with polarization usually include using alternate current measurements or applying direct current until resistance readings stabilize. This paper presents simple two-probe resistance sensing technique with DC being applied to the specimens as single square waves. Suggested approach is experimentally validated on the samples of CNT–cement composites. No polarization was observed in tested specimens when the periods between measurements were larger than 3 min. Such frequency of measurements is quite acceptable for monitoring the stress state of structures under static loading.