Effect Of Graphene-based Nano Carbon Additives On The Piezoresistive Properties Of Cement-based Composites

Graphene-based nano carbon materials(GNCMs)with the excellent performances in mechanical strength,thermal conductance and durability have been widely used in the aspects of chemistry,energy and materials.The self-monitoring function of building materials is important to achieve smart buildings.To this end,this study investigated the effect of GNCMs on the piezoresistive properties of cement-based composites.The results would provide scientific bases for the fabrication and design of piezoresistive building materials,which pave paths to smartly self-monitoring buildings.The main work and achievements of this study include:(i)The dispersion efficiency of GNCMs in different solutions was studied.It was found that the melamine dispersant and the ultrasonic treatment can stably maintain the dispersion of the GNCMs for at least 4 h;and when the mass ratio of the dispersant to the GNCMs exceeds 0.5,the dispersion efficiency can be remarkably improved.(ii)This study involved three typical GNCMs,i.e.,graphene-nanoplatelets(GNP),carbon-nano tubes(CNT)and graphene oxide(GO),and tested their effects on the piezoresistive properties of cement-based composites.It was found that both CNT and GNP can significantly affect the piezoresistive properties of the cement-based composites;and GNP showed a stronger toughening effect on the composites than CNT.(iii)The effect of GNP content on the piezoresistive properties of cement-based composites was investigated.It was found that when the GNP content is between 0.1%and 0.5%,both the piezoresistive and mechanical properties of the GNP-modified cement composites can be enhanced.The piezoresistive reactions of the composites rely on the interfacial actions between the conductive fillers and the cement matrix.Especially under low stresses,these interfacial actions play a leading role,so the electric resistance changes greatly.However,when the GNP content reaches 1%,the piezoresistive sensitivity would be reduced comparing to the results of the reference group.The formation of conductive paths inside the composites that weakens the interfacial effects accounts for this observation.(iv)The hybrid blends of GNP and CNT into cement were performed to further tune the piezoresistivity of the cement-based composites.It was found that CNT can further improve the piezoresistive sensitivity of the composites under high stresses.An optimized mix of 0.25%GNP and 0.25%CNT was found to show the most sensitive piezoresisty.Overall,both GNP and CNT can improve the piezoresistivy of cement-based composites but these effects rise in different contents and stresses.The results and findings of this study will lay the foundation for the fabrication and design of piezoresistive building materials with the promised pespectives in developing smart buildings.