Effect of multi-walled carbon nanotubes on durability of high-strength slag-based geopolymer

Abstract

The effect of multi-walled carbon nanotubes (MWCNTs) on the durability of high-strength slag-based geopolymers was investigated. The control variables were the MWCNT content and MWCNT/dispersant and water-cement ratios. A total of 144 specimens were exposed to carbonization, freeze-thaw cycles, and chloride migration (RCM). The microstructure of the geopolymers before and after durability testing was observed using scanning electron microscopy (SEM). The modification of pore structure of geopolymer by MWCNTs was measured by mercury intrusion porosimetry (MIP). The composition of the materials was analyzed using X-ray diffraction (XRD), and the contents of the materials were determined quantitatively using thermal gravimetric analysis (TG). When the MWCNT content and water-cement and MWCNTs/sodium dodecyl sulfonate (SDS) ratios were 0.45 wt%, 0.55, and 2.5:1, respectively, the carbonization depth and carbonization strength of the geopolymers were 69% and 176% of those the control group, respectively. The loss rate and relative dynamic elastic modulus after freeze-thaw were 28% and 121% of those of the control group, respectively. The Cl− diffusion depth and diffusion coefficient were 63% and 84% of those of the control group, respectively. Water-cement ratio affected the internal structure and crystallinity of geopolymer. MWCNTs mixed with SDS to modify geopolymers, the main function of MWCNTs was to densify the matrix and improve the internal cracks and pores. However, the excess SDS caused structural foaming and reduced the durability of the geopolymer.