Abstract: A thorough study of the effect of reinforcement of OPC mortars with pristine and functionalized multiwall carbon nanotubes (MWCNTs) on the fracture behavior of the nanocomposite is presented herein. The critical values of fracture toughness, KIC; strain energy release rate, GIC; crack tip opening displacement, CTODc; and critical crack length, ac of 3, 7, and 28 days Portland cement mortars, reinforced with well dispersed carbon nanotubes, were experimentally determined. Prismatic notched specimens of neat mortar and mortars reinforced with 0.1 wt% pristine and functionalized MWCNTs were subjected to a three point closed loop bending test, using the crack mouth opening displacement (CMOD) as the feedback signal. The fracture parameters of the nanoreinforced mortars were then determined using the two parameter fracture model. Both pristine and functionalized carbon nanotubes demonstrated excellent reinforcing efficiency and toughening capability: fracture toughness was improved by 125%, strain energy release rate by 131%, crack tip opening displacement by 25%, and material length by 47%.
