The appropriate curing methods for 3D-printed cement-based materials have not yet been clearly defined, thus restricting their durability in cold regions. This study was to investigate the effects of natural curing (NC), standard curing (SC), high-temperature curing (T₆₀), saturated Ca(OH)₂ solution curing (SCH), and internal curing withabsorbent polymer (SAP) on the performance of solid waste-based 3D printed mortar (3DFGCM). The objective was to establish quantitative relationships among curing methods, mechanical anisotropy, frost resistance, and pore structure, thereby providing a theoretical foundation for improving the service life of 3D printed structures in cold regions.

The fly ash-slag-cement based mortar (FA : GGBS : OPC=1 : 2 : 7) was prepared at a sand-to-binder ratio of 1 : 1 and a water-to-binder ratio of 0.3. After vibration casting and 3D printing of the slurry, the specimens were naturally cured for 1 day and then divided into five groups for further curing. The 28-d compressive strength and anisotropy were tested in the X, Y, and Z directions. After 28-d curing under respective conditions, the specimens were immersed in water at 15-20 ℃ for 2 d before undergoing freeze-thaw cycles. The mass loss rate, relative dynamic elastic modulus, and strength loss rate were measured. The pore structure was analyzed before and after freeze-thaw cycles to determine parameters such as air content, chord length distribution, and spacing factor. Finally, a damage evolution model based on the Weibull distribution was established to predict service life, and a neural network was used to map the relationship between pore parameters and damage.

This study systematically investigates the effect of curing method (i.e., NC, SC, T₆₀, SCH, and SAP) on the performance of 3D printed fly ash-slag-cement-based mortar (3DFGCM). The comprehensive analysis of mechanical anisotropy, frost resistance, and pore structure, combined with freeze-thaw models and service life prediction models indicates that the 28-d compressive strength and isotropy coefficient of 3D printed specimens are lower than those of cast specimens. Among the curing methods, 3D-SC demonstrates the most significant enhancement in the 28-d compressive strength, while the SAP increases the 28-d compressive strength to 36.8 MPa, which is increased by 41.17%, compared to the NC group, with the lowest anisotropy coefficient (i.e., 0.187). The frost resistance of 3D printed specimens varies significantly. The 3D-NC and 3D-T₆₀ groups both fail after 125 freeze-thaw cycles, the 3D-SAP group exhibits the optimum frost resistance, retaining 61.5% of its dynamic elastic modulus and showing a mass loss of 4.57% after 150 freeze-thaw cycles. Its closed micropores and humidity balance mechanism effectively mitigate frost heave damage. In terms of the pore structure, 3D printed specimens exhibit distinct elliptical pores. The 3D-SCH group shows a limited improvement in cavity and interlayer cold joint defects, with large pores accounting for 75% more than those in the 3D-SAP group. The incorporation of SAP improves process-induced defects and significantly inhibits pore coarsening. With the relative dynamic elastic modulus as an index, the Weibull damage and service life prediction models are applied to assess freeze-thaw damage and service life of 3DFGCM, with R² of > 0.98. The 3D-SAP group performs optimally, with a predicted service life of 15.9 years. Furthermore, based on BP neural networks, the effective correlations are established between pore structure parameters and the Weibull-predicted damage and service life, with R² of > 0.97.

In terms of mechanical anisotropy, the strength of 3D-printed specimens followed a decreasing order of Cast>X>Z>Y. The SAP curing resulted in the lowest anisotropy coefficient (i.e., 0.187), with a 41.2% increase in the strength, compared to the NC group. For the frost resistance, after 150 freeze-thaw cycles, the SAP group retained 61.7% of its dynamic elastic modulus and exhibited only 4.57% mass loss. In contrast, the NC and T₆₀ groups failed after 125 cycles due to pore coarsening. In terms of the pore structure, the initial air content of 3D-printed specimens was 1.5 times higher than that of cast specimens. After freeze-thaw cycles, the total chord length of the NC group was increased by 65.3%. The SAP effectively inhibited pore coarsening, with large pores accounting for only 36%, representing a 75% reduction, compared the NC group. Finally, a damage evolution equation was established based on the Weibull distribution model, predicting a service life of 15.9 years for 3D-SAP in cold northwestern regions. The BP neural networks were employed to predict damage and lifespan based on microscopic pore structure. This study could provide a reference for the design of methods and frost resistance optimization in 3D-printed construction materials.