Effect of Addition of CNTs on Properties of Concrete

Abstract

Carbon nanotubes (CNTs) are now known to be the materials of 21st century and are currently receiving a lot of interests due to its extremely good mechanical properties. CNTs resemble single or multiple graphene sheets rolled up in a tube or a series of tubes. The unique graphene structure endows CNTs with extraordinary characteristics. While their density is less than that of steel or glass fiber, CNTs have an elastic modulus in the terapascal range, yield strength of approximately 20-60GPa, and yield strain of up to 10 percent. CNTs have high aspect ratios and strong van der Waals self-attraction between nanotubes and tend to form CNT bundles. When CNTs are used in concrete, they were expected to provide mechanical reinforcement between hydration products of cement with nano-scale dimensions. CNTs/CNFs achieves enhancement effect by nucleation, increasing the amount of C-S-H gel of high hardness, improving pore structures, controlling nanoscale cracks, improving the early strain capacity and reducing autogenous shrinkage etc. These mechanisms would also improve the durability of cement-based materials. In the present study, the effect of addition of CNTs on strength and durabilty properties of concrete has been studied. Five different mixes were prepared, in which fly ash was utilized in replacement with cement (20%) by weight and CNTs in different percentages (0.025%, 0.048%, and 0.08%) to (cement + fly ash) by weight. The evaluated strength properties (compressive strength, splitting tensile strength and young’s modulus) and durability property (permeability) were compared with the sample containing 20 percent fly ash only and with each other on different utilized percentages of CNTs. Increase in compressive strength, splitting tensile strength and young’s modulus was observed in the mix incorporating 0.08% CNTs and FA on comparison with mixture containing 20 percent fly ash. Also the mix incorporating 0.08% CNTs and FA exhibited low permeability to chloride ions and hence enhancing the durability properties of concrete mix.