Impact of pre-soaked lime water carbonized recycled fine aggregate on mechanical properties and pore structure of 3D printed mortar

Compared to natural fine aggregate, recycled fine aggregate has disadvantages such as high water absorption and poor strength. Accelerated carbonization is considered a method to enhance recycled aggregate performance. However, the lack of substances available for carbonation reaction in old cement mortar restricts the enhancement of RFA performance. In this study, a pre-soaked lime-water carbonization method was employed to enhance carbonization efficiency and improve cement mortar performance by introducing additional sources of calcium. Therefore, the focus was on investigating the effects of pre-soaked lime-water carbonization-treated recycled fine aggregate with different replacement rates (0%, 30%, 50%, 70%, 100%) on the mechanical properties of 3D printed mortar. In addition, combining XRD、SEM-EDS and X-CT microscale testing methods, the study analyzed the influence of carbonized recycled fine aggregate on the pore structure of 3D printed recycled mortar. The purpose was to reveal the reinforcement mechanism of pre-soaked lime water composite carbonization. Experimental results showed that the pre-soaked lime water carbonization method improved the physical properties of recycled fine aggregate, with the most significant decrease in water absorption rate, which decreased by 53.89%. Incorporating appropriate carbonized recycled fine aggregate can enhance the mechanical properties of 3D printed mortar, increase interlayer bonding strength, reduce mechanical anisotropy and overall porosity, and improve pore defects. Defects on the aggregate surface are filled with CaCO3 carbonization product, improving the pore structure and strengthening the interfacial transition zone, thus enhancing the resistance of 3D printed recycled mortar to external forces. The findings of the present work not only improve the utilization of recycled sand, but also provide methods and ideas for improving the properties of 3D printed recycled mortar.