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Decoupling the individual effects of multiwalled carbon nanotubes (MWCNTs) and surfactants when used as reinforcement materials in cement-based composites is aimed in this study. Powder MWCNTs were dispersed in deionized water using different types of surfactants as chemical dispersing agents and an ultrasonic tip processor. Cement pastes with carbon nanotubes additions of 0.15% by mass of cement were produced in two steps: first, the MWCNT/surfactant dispersions were combined with the mixing water, and then, cement was added and mixed until a homogeneous paste was obtained. Mechanical properties of the pastes cured at 7 days were measured, and their fracture behavior was characterized using the linear elastic finite element analysis. It was found that the reinforcing effect of MWCNT was masked by the negative effect of surfactants in the cement matrix; nevertheless, nanotubes were capable of increasing both stress and strain capacity of the composite by controlling the crack propagation process at the tip of the crack.

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Carbon nanotubes as additions in Portland cement based matrices have a great potential to improve the mechanical properties of mortars and concretes; however, little work has been done regarding the effect that they have on the chemical durability of the cement matrix and reinforcing steel. In this work, carbon nanotubes are dispersed in water solution with Triton X 100 surfactant and blended in Portland cement mortars. A sharp decrease in compression resistance was observed at all curing ages (7, 14, 21 and 28 days) while a depth increase in the carbonation profile was found, which is associated with a decrease in the matrix durability.