Investigation of interlayer bonding and pore characteristics in 3D-printed high-strength mortar incorporating recycled lightweight aggregates
Hamid Reza Bayat, Sadegh Karimpouli, Liming Yang, Hamed Lamei Ramandi, Alireza Kashani
Abstract
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/m 3 , 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. • Lightweight aggregates reduced thermal conductivity by up to 58 % in 3D-printed concrete. • Micro-CT analysis revealed 33 % peak porosity at the interface of printed layers. • Pore structure at interlayer interfaces is key to strength and thermal performance. • Sustainable use of fly ash cenosphere and expanded glass enhances energy efficiency of 3DCP.