Effect of pore structure on durability and mechanical performance of 3D printed concrete

•The mix of 3DPC was designed based on the MA&A model.•The anisotropy mechanism of 3DPC was explained by CT scanning.•The distribution, connectivity, and porosity of pores in 3DPC were investigated.•Effect of pore structure on durability and mechanical properties of 3DPC was studied.•Effect of freeze-thaw cycle on mechanical properties of 3DPC was studied. The application of 3D printed concrete (3DPC) technology in the construction industry has become widespread in recent years. This paper provided a method for the 3DPC mix design and investigated the mechanical performance and durability of 3DPC. In this study, two optimized mixes were obtained based on the particle dense packing theory and the least squares method for calculating the proportions of binder for 3DPC. The microstructure of 3DPC was investigated by X-CT scanning to characterize its porosity for discussion of the anisotropic mechanical performance in the 3DPC. In addition, the frost resistance and chloride ion penetration resistance of 3DPC had been investigated. The results showed that the pore connectivity of 3DPC was better than that of casting concrete and the pores accumulated near the interface. In addition, the porosity calculation results showed that the porosity of the interface between layers was lower than that of the interface between filaments in 3DPC. All specimens of 3DPC showed excellent frost resistance with a maximum mass loss of only 0.18% and the average flexural strength and compressive strength of 3DPC were only reduced by 31.2% and 21.0% respectively after 300 freeze–thaw cycles. The maximum chloride migration coefficients for the 3D printed concrete specimen was 79 × 10-14 m2/s and the glass fiber enhanced the chloride ion penetration resistance of the specimens.