Multiscale modeling of the mechanical properties of carbon nanotube reinforced cement composites.

Carbon nanotube, a product of chemical exfoliation of graphite, is a suitable additive for use as nanoreinforcement in cement-based materials due to its high aspect ratio, good water dispersibility and excellent mechanical properties. In the present study, the effect of volume fraction, aspect ratio, distribution orientation and interaction between surfaces on the mechanical properties of cement matrix reinforced with carbon nanotubes using multi-scale modeling was investigated. To Model in the Abaqus software, with the conceptual understanding of the volume representative element, a developed MATLAB and Python scripts were applied. To observe the interphase behavior between the matrix and fillers, the cohesive surface theory was used. Also, the output results of molecular dynamics modeling was used to determine the cohesive surface parameters. Modeling was done in the states of full and limited bonding between two phases in nano-compsite with compressive axial loading. The cement models with 0, 0.5, 1, and 1.5 vol% with aspect ratios of 10 and 20 were evaluated and discussed. Furthermore, the distribution effect was studied by defining the nanotubes to be parallel, perpendicular and random regarding the force direction. The results showed that increasing the volume fraction of CNTs improves the yield strength and toughness of the samples. Increasing the CNT aspect ratio from 10 to 20 leads to an increase of elastic limit and an improvement of plastic behavior of the next matrix. Finally, the cohesive modeling of the interactions of matrix and CNT eventuated in 3 to 6% reductions per 0.5 and 1% CNT/cement composites.