Pore structure characteristics of concrete composites with surface-modified carbon nanotubes

Abstract

The macroscopic properties of carbon nanotubes (CNTs) modified reactive powder concrete (RPC) composites are closely related to their pore structure characteristics, but the structural nature of PRC composites and the effect of CNTs on their pore structure remain unclear. To comprehensively understand the pore structure of RPC composites with surface-modified CNTs and then control their properties, both the mercury intrusion porosimetry (MIP) and low-field nuclear magnetic resonance (LF-NMR) technologies were used to characterize the pore structure characteristics of RPC composites. Experimental results showed there exist large number of nano-scale pores (mainly interlayer and gel pores) with the radius range of 0.3–20 nm in RPC composites. All types of surface-modified CNTs incorporated in this study reduce the pore content and size of RPC composites, thereby modifying the pore structure of RPC. However, different CNTs present varying effects on the pore (especially nano-scale pore) structure characteristics. Among all surface-modified CNTs, the hydroxyl functionalized and nickel-coated CNTs cause the structural shrinkage of C-S-H gel, while the carboxyl functionalized CNTs induce the transformation of some nano-scale pores inside the gel. The effects of surface-modified CNTs on the pore structure of RPC composites are mainly on the nano- and micrometer scale. CNTs can not only increase the matrix compactness of RPC composites and enhance the network structure of hydration products, but also induce the pore water conversion inside C-S-H layers.