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Highlights • CNTs and CNFs are both the nano-structured fibrous materials with excellent properties. • The dispersion of CNTs/CNFs is the decisive factor affecting the performance of composites. • The incorporation of CNTs and CNFs affects the variety performance of cement-based materials. • CNTs/CNFs-modified cement-based composites have broad application prospects. Abstract CNTs and CNFs are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites' properties when adding CNTs/CNFs into composites. This paper briefly introduces the CNTs'/CNFs' basic properties and dispersion methods, and elucidates the properties of cement-based composites recombining CNTs/CNFs, including the mechanical property, the deformation property, the durability property, the thermal conductivities and electrical conductivities. This paper also summarizes the problems existing in present research, and gives some proposes for future study. [ABSTRACT FROM AUTHOR]

• The salt freeze-thaw resistance of concrete is better when the MWCNTs content is low. • Air content and void specific surface area are most closely related to the change of compressive strength of MWCNTs-FAC. • The average chord length and void spacing factor have the greatest influence on the damage of MWCNTs-FAC. 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. [ABSTRACT FROM AUTHOR]