Coupled effect of MWCNTs concentration and induced pore structures on compressive performance and elastic modulus of ultra-high toughness cementitious composites: Experimental and theoretical studies

Due to the superior mechanical properties and electrical conductivity of multi-walled carbon nanotubes (MWCNTs), their integration into cementitious composites can improve compressive strength and self-sensing capabilities. However, balancing high mechanical strength with high conductivity is challenging as high MWCNT dosages can impede strength development. We addressed this by studying the effect of MWCNTs concentration (0-1.1 wt% of cementitious binders) and induced pore structures on the compressive performance and elastic modulus of ultra-high toughness cementitious composites (UHTCC), both experimentally and theoretically. It was found that as the MWCNTs concentration increased, the porosity continued to increase, while the compressive strength fluctuated. Two failure patterns were identified, i.e., quasi-brittle failure and ductile failure. Analysis showed MWCNTs could promote cement binder hydration, increasing matrix density but the strength development was curbed by increased porosity. A balance was achieved at 0.7 wt% MWCNTs. Further investigations using the Eshelby-Mori-Tanaka method discussed how MWCNT concentration, mechanical properties, distribution, porosity, and pore geometry influenced the elastic modulus. Ultimately, we developed a UHTCC-MWCNT composite with 1.1 wt% MWCNTs, which exhibited substantial improvements in compressive strength (44.85 MPa) and conductivity (9.78x10(-3) S/m), showing increases of 22.18 % and 18,132.6 % respectively, compared to the reference group.