Role of multiwalled carbon nanotubes as shear reinforcing nanopins in quasi-brittle matrices

Multiwalled carbon nanotubes (MWCNTs) have been widely used to enhance nanocomposites under tension, whereas their influences on shear resistance have been largely overlooked. To verify the feasibility of MWCNTs as a shear reinforcement material, here we report the experimentally observed shear reinforcing effect of MWCNTs on quasi-brittle cementitious material. The enhancing mechanism is identified based on the investigations of the atomic and nanomechanical interactions between MWCNTs and porous-silica-based matrices by nonequilibrium molecular dynamics simulation. The experiment reveals that the addition of 0.036 wt % MWCNTs in cementitious material causes up to 32% increment in the shear resistance. The atomic simulation shows that MWCNTs can work as nanopins under shear, enhancing the nanofriction that accounts for up to 95% of the increase in fracture energy. The findings also suggest that nanomechanical properties and phase composition of matrices and the distribution of MWCNTs play critical roles in shear reinforcing. These understandings provide the base for developing enhanced nanocomposites applied in such as grouting projects and adhesive industry where high shear resistance is required.