حمیدرضا ناصر سعید

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.

The utilization of steel fiber reinforcement concrete (SFRC) in practical applications is gained considerable attention owing to its acceptable strength (Nili & Afroughsabet, 2010; El-Dieb, 2009) and durability. Taking to account, SFRC in constructions may inevitably subjected to short duration dynamic loading, the impact resistance of SFRC which cured under different curing conditions must be well documented. To evaluate the resistance of SFRC under impact loadings, a variety of test procedures have been suggested (ACI Committee 544, 1996) . In this study, the drop-weight test as recommended by ACI committee 544 (ACI Committee 544, 1996) were utilized.

Application of nanoparticles in cement, regarding their synthesis and utilization procedure, provides various mechanical, electrical and thermal properties to cement based composites. The superior properties of carbon nanotubes (CNTs) have made them as one of the most beneficial nano-reinforcement material. On the other hand, metal particles have been known to be effective for enhancing electrical properties. Accordingly, it seems that the synergistic incorporation of CNTs and copper particles can introduce suitable piezoelectric properties to cement matrices. To this end, in the current investigation, in order to prepare the reinforcement material, copper coated CNTs were prepared using an efficient electroless deposition process. The synthesized samples were characterized using SEM, TEM, XRD, TGA, ICP and AAS. Our results revealed that the process covers most surfaces of the CNTs. Furthermore, the calculated bath efficiency showed to be more than 99%