Compressive properties and underlying mechanisms of nickel coated carbon nanotubes modified concrete

Abstract

Nickel coated multi-walled carbon nanotubes (Ni-MWCNTs) having exceptional mechanical properties, thermal conductivity and dispersibility can effectively overlap in cementitious matrix, thus forming an enhanced and thermal conductive network. They are therefore a promising nanofiller for modifying cement and concrete materials. This paper studies the compressive properties of reactive powder concrete (RPC) filled with different aspect ratios of Ni-MWCNTs, including strength, toughness, Young's modulus and Poisson’s ratio. It is concluded that the incorporation of 0.06 vol.% Ni-MWCNTs with an aspect ratio of 1500 maximally increases the compressive strength and toughness of RPC by 20.24%/20.39 MPa and 43.89%/56.35 (N·m), respectively. However, Young's modulus and Poisson's ratio of Ni-MWCNTs modified composites do not significantly be improved. Besides, a constitutive model of Ni-MWCNTs reinforced RPC under uniaxial compression is established based on the continuum damage mechanics theory, reasonably predicting the relationship between compressive strength and deformation of composites. The modification mechanism of Ni-MWCNTs is also investigated through the temperature distribution monitoring inside composites, Scanning Electron Microscope (SEM) observation and energy dispersive x-ray spectrometry (EDS) analysis of Ni-MWCNTs reinforced RPC. The thermal conductive network formed by Ni-MWCNTs in matrix reduces the temperature difference and improves the temperature uniformity inside composites, thereby decreasing thermal stresses, primary cracks and defects of composites. Furthermore, the incorporation of Ni-MWCNTs makes the RPC microstructures dense, decreases the average CaO to SiO2 ratio, and inhibits the development of cracks inside RPC, thus achieving effective enhancement to RPC.