Influence of single-walled carbon nantotubes structure and density on the ductility of cement paste

The main objective of the present work is to investigate the possibility of using new reinforcing material, such as carbon nanotubes (CNTs), into the cement matrix. To this end different atomic models with various CNT's types were created. The 11 Å-tobermorite with Ca/Si ratio of 1 was selected here as prototype of the calcium silicate hydrate (C-S-H) gel, which keeps the concrete components together. Molecular dynamics simulation method was employed to evaluate the different mechanical and physical quantities by considering the best type of carbon nanotube in 11 Å-tobermorite. Besides, results provide the information about brittle/ductile behaviors of the composite, modified by CNTs and give clear explanation about the anisotropy of these systems. In addition, various models representing the concrete modified by CNTs were constructed to study the density effect of carbon nanotubes in the cementitious composites. Optimal concentration of CNT was fixed and the best concentration allowing increase bulk, shear and Young's moduli is 5.2% of weight of tobermorite.