Today, studies on nanotechnology applications in the construction industry are looking for a solution to reduce the use of cement and consequently to reduce the emission of pollutants in the environment. In this regard, the effect of different percentages of the functionalized multi-walled carbon nanotubes with carboxylic groups (MWCNT) on the modification of mechanical and microstructural properties of hardened cement paste was investigated. The addition ratios of Portland cement with the same weight of MWCNT-COOHs were 0, 0.025, 0.05, 0.1, and 0.2 weight percent (wt%). Moreover, the mechanical and microstructural properties of the hardened cement paste were investigated by the use of Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), X-powder, scanning electron microscope (SEM) and atomic force microscope (AFM) techniques. The results show that replacement of cement with 0.05 wt% of the functionalized carbon nanotube, as the optimal amount, can be considered both for improving mechanical and microstructural properties.
