عنوان مقاله [English]
Carbon nanotubes, due to their particular mechanical, thermal, and electrical characteristics, have revolutionized the electronics industry and have become the basis of nanotechnology as a discipline of technology and science. The major weakness of reinforced concrete structures exposed to fire is the deterioration of steel rebars which the use of nano materials such as multi-walled carbon nanotubes can solve this weakness. Multi-walled carbon nanotube has been known for its advantages, including high specific surface, various electrical properties, too high young's modulus ( about 2000 GPa ), very strong bond between carbon atoms, high tensile strength (about 50 GPa), high flexural strength and electrical and thermal conductivity. In this paper, the effect of multi-walled carbon nanotubes on the properties of concrete was evaluated in the post-heat treated condition. Following this, a number of cylindrical specimens (10 x 20 cm) including multi-walled carbon nanotubes in different percentages of 0.5, 1 and 1.5% by weight of cement were cast. Later on, concrete specimens in the electric furnace were exposed to temperatures of 25, 100, 250,500 and 700°C and after cooling down, compressive and tensile strength tests and SEM test were carried out on them. The results showed that the use of multi-walled carbon nanotubes increased compressive and tensile strengths of concrete up to 138% and 88%, respectively. In addition, by increasing multi-walled carbon nanotubes in concrete, dissipation of energy and modulus of elasticity of concrete specimens were up to 2 times more than that of control concrete specimens. Furthermore, after conducting tests, it was clear that the crack width has been decreased by using multi-walled carbon nanotubes in concrete; because, there was a strong bond between cement paste and multi-walled carbon nanotubes. The SEM test results indicated that a strong bond between concrete particles exists at the room temperature and upper than that.