A two-step homogenization micromechanical model for strain-sensing of graphene reinforced porous cement composites

The incorporation of graphene and its derivatives into cement for electrically conductive composites is currently under extensive investigations due to their potential applications as smart materials for large-scale self-sensing structures. It is of great importance to develop theoretical models to predict the response of the electrical conductivity of the cement composites when subjected to mechanical deformation. Experimental studies have demonstrated that pores and rippled graphene fillers exist in the cement composites. However, currently there are limited theoretical models to predict the electrical conductivity and piezoresistive properties of the cement composites with incorporating the effects of pores and graphene ripples. To address the research gap, this paper develops a two-step micromechanical modelling to predict the effective electrical conductivity and the response of conductivity to compression strain of graphene nanoplatelet (GNP) reinforced cement composites (GNPRCCs) with considering the effects of pores and graphene ripple for the first time. The effective medium theory and Mori-Tanaka model are employed to homogenize the GNP and pores as inclusions with considering several influencing mechanisms. Parametric study is carried out to identify the effects of the attributes of GNPs, pores and electron tunnelling on the electrical and piezoresistive properties of the GNPRCCs. It is found that the piezoresistive response is proportional to porosity when the conductive behavior of GNPRCC is dominated by the tunnelling effect. Increasing porosity has a negative impact on the strain-sensing performance of the GNPRCCs once the conductive network is formed.