Synthesis, design and piezo-resistive characteristics of cementitious smart nanocomposites with different types of functionalized MWCNTs under long cyclic loading

In recent years, carbon nanotubes (CNTs) incorporated smart cement composites have attracted significant attention as it opens up a new avenue to develop new class of sensors, in general, and uniquely enables the structural materials to reflect the internal stress state, in particular. However, dispersion of CNTs, threshold limit, polarization effect, type and design of electrode, effect of functionalization of CNTs etc. on piezo-resistive properties of cementitious nanocomposites need further investigations. The present study describes the systematic approach for developing cement based smart nanocomposites exploiting the unique capabilities of functionalized MWCNTs and comprehensive studies on performance under monotonic- and long reverse cyclic-loading. Three different types of multiwalled carbon nanotubes (MWCNTs) like pristine MWCNTs, hydroxyl (-OH) MWCNTs and carboxyl acid (-COOH) MWCNTs are considered. The response of cement based smart nanocomposites under cyclic compression load was measured in terms of fractional change in resistivity (FCR) where type and dosage of CNT, type of electrode are the parameters. The test results indicate that the performance of the smart composite with COOH-MWCNTs is superior compared to other types and the gauge factor of the composite is found to be as high as 451. The study also emphasizes the role of stabilization, tunneling effects and formation of conductive paths in imparting the piezo-resistive properties in porous, nonconductive materials like cement composites.