Characterization of adhesion strength between carbon nanotubes and cementitious materials

Multi-walled carbon nanotube (MWCNT) and carbon nanofiber (CNF) additions increase the elastic modulus, flexural strength, and toughness of Portland cement concrete. However, the interaction mechanism between cement constituents and these nanomaterials is not fully understood. A modified MWCNT-coated atomic force microscopy (AFM) probe is developed by coating a silica particle with oxidized MWCNT through layer-by-layer assembly and adhering it to a tipless AFM cantilever. The probe allows measurement of adhesion between MWCNT and the substrate with a force control procedure. SEM-EDS is acquired in the same region as AFM measurements through a benchmarking scheme to correlate chemistry with the measured adhesion. Statistical deconvolution shows C-S-H regions have lower adhesion to MWCNT than intermixed regions (C-S-H/Clinker). Furthermore, in C-S-H regions, the normalized adhesion strength increases with calcium concentration. This result is due to the higher interaction between the oxygen functional groups in the MWCNT surface and the calcium in the substrate.