Multi-walled carbon nanotube (MWNT) reinforced cement composites (MWFRCs) were prepared with surfactant dispersion,
ultrasonic treatment, and subsequently high-speed shear mixing processes. These MWFRCs were characterized in the fracture
toughness property with single edge notch bend method. As found, the addition of nanotubes improves the stress-intensity
factor (KIC), critical crack mouth opening displacement (δC) and flexural strength
(σs) of the cured nanocomposite, significantly. The maximal enhancement arrives up to 56.4%,
119.4%, and 54.8%, compared to the baseline, respectively. These achievements are mainly attributed to the superior
pulling-out effect of dispersed and tough MWNT fiber upon the notched cracks. Incorporation of acid-treated MWNT balances
the σs, KIC, and δC values. Additional nanophase carbon black mixed into
the above MWFRC further increases the corresponding fracture toughness, while additional short carbon fiber shows a negative
effect.