Improvement of interlayer performance of 3D printable magnesium oxysulfate cement-based materials by carbonation curing

This paper investigates the influence of fly ash (FA) incorporation and carbonation curing treatment on the interlayer bonding strength and permeability performance of 3D-printed magnesium oxysulfate cement-based (3DP-MOS) mortars. The interlayer bonding strength, permeability performance, pore structure, phase composition, microhardness, and elastic modulus of typical 3DP-MOS samples were systematically evaluated. The results show that carbonation curing significantly enhances the interlayer bond strength and alleviates the strength deterioration resulting from incorporating FA in 3D-printed samples. It also reduced interlayer permeability, particularly at interfaces prone to deterioration. Carbonation curing promotes the generation of magnesium carbonate hydrate crystals that interlace with phase 5 Mg(OH)₂·MgSO₄·7H₂O crystals, creating a network-like structure that refines the pore size distribution and reduces capillary and macropores. Additionally, carbonation curing increases interlayer microhardness by approximately 10 %, with greater improvements of 17.6 %–27.4 % observed at distances up to 1000 μm from the interlayer. The elastic modulus at 50 μm from the primary interlayer crack also increases from 23.5 GPa to 33.9 GPa, highlighting its role in optimizing the interlayer interface and micromechanical properties of 3DP-MOS mortars. Consequently, carbonation curing significantly alleviates the interlayer performance deterioration induced by 3D printing.