Dispersion and reinforcement efficiency of carbon nanotubes in cementitious composites

Cement pastes reinforced with various concentrations of functionalised and unfunctionalised carbon nanotubes (CNTs) with different aspect ratios were studied in terms of their dispersion and reinforcement efficiency. Mechanical strength was correlated with geometrical characteristics of CNTs, as well as the microstructure of reinforced pastes. Optimal CNTs of 0.05-0.1 wt% were found effective in increasing the flexural and compressive strength of reinforced pastes up to 36% and 27%, respectively. Efficiently dispersed CNTs were effective in bridging microcracks up to around 1 mu m width. The CNTs did not significantly affect the phase composition of cement pastes but accelerated the hydration process. Based on a proposed equation, strength improvement was correlated with CNT aspect ratio and volume concentration. This equation establishes guidelines for maximised strength development based on geometrical and compositional parameters; it can be used for more rational design of CNT-reinforced cement materials, covering different compositions, as well as types and amounts of CNTs.