Cement Composites Reinforced with Functionalized Carbon Nanotubes
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Cement Composites Reinforced with Functionalized Carbon Nanotubes Sergey Petrunin1, Viktor Vaganov1, Konstantin Sobolev2 1 Department of Nanotechnology and Theoretical Physics, Vladimir State University, Vladimir, Russia 2 Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, Milwaukee, USA ABSTRACT This paper reports on the effect of surface functionalization of multi-wall carbon nanotubes on the strength and structure of portland cement composites. Reference nanotubes and nanotubes functionalized by carboxylic groups are used in this research. Grafting of functional groups on the surface of the nanotubes allows the acceleration of cement hydration. It is established that the use of carboxylated nanotubes contributed to early strength development. The multi-wall carbon nanotubes reinforced composites are characterized by the high content of the calcium silicate hydrates and a very dense structure.
INTRODUCTION The development of nanotechnology has enabled the creation of concrete with improved physical, mechanical and durability characteristics [1, 2]. Carbon nanotubes (CNTs) have very unique properties: a very high Young's modulus of up to 630 GPa, strength up to 150 GPa, high electrical and thermal conductivity. Reinforcing the cement matrix by CNTs allows the development of material with enhanced performance characteristics [1-3]. In this paper, the effect of surface functionalization of multi-wall carbon nanotubes (MWCNTs) on strength, structure and composition of portland cement composites are investigated. Reference nanotubes and nanotubes functionalized by carboxylic groups are compared in the research. Cement composites modified by CNTs have improved strength, corrosion and freeze-thaw resistance in comparison with the reference [4-6]. However, the effective use of CNTs as a reinforcing material in concrete is complicated, because CNTs are chemically inert and, under the influence of Van der Waals forces, have a tendency to form agglomerates [7, 8]. Grafting of oxygen-containing groups on the surface of CNTs enables chemical interaction between the nanotubes and the cement matrix [9, 10]. It is established that oxygenized CNTs are involved in the hydration process of cement and form the bonds with the cement hydration products [11]. The interaction of carboxylated CNTs with cement hydration products is investigated. In this case, the adsorption of hydrates on surfaces of CNT is observed and resulted in a higher strength vs. concrete modified with reference CNTs.
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THEORY Materials Ordinary portland cement CEM I 42.5 R is used for the synthesis of CNT-reinforced composite. Silica sand with a fineness modulus of 2.8 is used as a fine aggregate. Polycarboxylate superplasticizer is used to enhance the stability of the CNT colloidal solution in water and reduce the agglomeration effects inherent to nano-objects. The MWCNTs are used as a reinforcing component for the composite. The initial MWCNTs are in the form of filaments with a diameter of 30-60 nm bound and rolled up into th
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