Grey entropy analysis of strength and void structure of carbon nanotubes concrete under the coupling of sulfate attack and freeze-thaw cycles

Abstract

This paper aims to investigate the primary and secondary effects of different void structure parameters (air content, specific surface area, spacing factor, and average chord length of voids) on the macroscopic damage of multi-walled carbon nanotube-fly ash concrete (MWCNTs-FAC) under the coupling action of sulfate attack and freeze-thaw cycles. Through coupling tests of sulfate attack and freeze-thaw cycles, as well as X-ray computed tomography (CT) scanning tests, analyzed how MWCNTs-FAC differ in their compressive strength and damage quantity as a function of the number of coupling cycles. The effect of different void structure parameters of MWCNTs-FAC on the compressive strength and the damage quantity was also discussed using the grey correlation entropy analysis. The results show that the addition of MWCNTs can effectively improve the salt freeze-thaw resistance of concrete. When the MWCNTs content is 0.05 wt%, MWCNTs-FAC has the best improvement effect of salt freeze-thaw resistance. When the content of MWCNTs remains constant, the compressive strength of MWCNTs-FAC decreases, and the damage quantity increases as the air content, spacing factor, and average chord length of voids increase. The effect of specific surface area on the macroscopic damage of MWCNTs-FAC is exactly the reverse. Under salt freeze-thaw conditions, air content and specific surface area are two major factors influencing compressive strength, whereas average chord length and spacing factor are the main elements influencing damage quantity.