Residual mechanical properties of mortars containing carbon nanomaterials exposed to high temperatures

•Pioneering evaluation of residual properties of mortars with CBN at fire conditions.•Low MWCNT and CBN contents increase mechanical properties in the 200–600 °C range.•High MWCNT and CBN contents decrease mechanical properties in the 200–400 °C range.•MWCNT and CBN decomposition after 500 °C releases vapor pressure and mitigates cracks.•Highest residual strength/stiffness from 200 to 600 °C in mortars with 3% of CBN. Carbon-based nanomaterials can provide improvements of the mechanical behavior of cementitious materials at high temperatures. This research investigated mechanical properties and microstructure of 92 composites containing different concentrations of multi-walled carbon nanotubes (MWCNT) and carbon black nanoparticles (CBN), and exposed to temperatures up to 600 °C. A comprehensive comparison between the post-fire performances of these different carbon-based nanomaterials was made. Values of moisture loss and microstructure changes due to temperature increases elucidated variations of different mechanical properties. The addition of 3% of CBN and 0.4% of MWCNT increased the post-fire residual compressive strength, static and dynamic elastic modulus of plain mortars.