Study On Piezoresistive Effect Of High Ductility Cement-based Composites Containing Graphene Under Direct Tension

Smart concrete has many advantages such as self-diagnosis,self-regulation,self-enhancement and self-healing and so on.Based on these characteristics,smart concrete can be used to perform structural health monitoring(SHM)and crack self-healing for civil engineering structures.But the tensile strain sensing range of smart concrete is too small,which limits its applications in SHM.Due to high ductility of strain hardening cement-based composites(which can be referred to SHCC),it is possible to obtain high ductility self-sensing smart concrete under uniaxial tension.In this paper,the tensile mechanical properties,electrical conductivity and the piezoresistance effect of SHCC containing graphene nanoplatelets(GnPs)or graphene oxide(GO)are investigated.Then the analytical model is established to study the resistance vs tensile strain relationship of SHCC containing graphene.The main works are as follows:(1)The mechanical and electrical properties of SHCC with different contents and different kinds of graphene were studied through experiments.The electrical conductivity and tensile strength of GnPs-SHCC was higher than that of conventional SHCC when the content of GnPs was below 0.8%.There were multiple fine cracks on the samples under unaxial tension,and the piezoresistance effect of GnPs-SHCC was good under cyclic loading.The tensile strength and ductility of GO-SHCC decreased in comparsion with conventional SHCC while the contents of GO was 0~0.05%.Thesensitivity to tensile strain of SHCC containing GO was higher than that of ordinary SHCC.(2)The sensing properties of SHCC containing graphene to the opening of crack was analyzed on specimens with the prefabricated notch.The relationship between the resistance change and the width of crack was obtained.Results showed that the resistance of GnPs-SHCC was sensitive to the width of crack,and within the elastic phase the resistance increased linearly with the increasing crack width.Within the strain hardening phase,the increase in resistance changed with the increasing crack width was more than that in elastic stage.(3)The piezoresistance analytical model was established by combining the relationship between the resistance change and the crack width mentioned above with the probability density function of the crack width distributions of SHCC containing graphene.The probability density function of the crack width distribution conformed to the lognormal distributions.The curve of resistance change with strain was consistent with the experimental results.