Investigation of interlayer bonding and pore characteristics in 3D-printed high-strength mortar incorporating recycled lightweight aggregates

This study explores the incorporation of recycled lightweight aggregates i.e. fly ash cenosphere (FAC) and expanded glass (EG) into 3D-printed cementitious mortar to enhance both thermal insulation and sustainability. The novelty lies in examining how these aggregates impact the mechanical and thermal properties of 3D-printed structures, while also analyzing the pore structure, particularly at the critical interface between successive printed layers. Replacing sand with 60 % FAC (C60) and 65 % EG (G65) resulted in a lightweight mortar with a density of 1800 kg/m3, but also led to reductions in compressive, interlayer bonding, and flexural strength. X-ray microtomography (μ-CT) analysis revealed significant variations in porosity, particularly at the interlayer region where porosity peaked at around 33 %. The thermal conductivity of the printed samples was reduced by up to 58 %, driven by both the lightweight aggregates and the porous interlayer structure. Despite the weakened mechanical properties, the enhanced thermal performance of the 3D-printed samples suggests potential for sustainable, energy-efficient construction. The findings highlight the critical role of pore structure, especially at layer interfaces, in determining the strength and insulation properties of 3D-printed mortars. This work provides valuable insights into the trade-offs between strength and thermal insulation when using lightweight aggregates, offering a pathway to more energy-efficient and sustainable 3D-printed buildings with potential lower operational carbon footprints for 3D-printing construction.