Recycled cork aggregate for 3D concrete printing: Rheology, pore-driven anisotropy mitigation, and low-carbon thermal buffering

This study presents a multiscale investigation of 3D-printed concrete incorporating recycled cork aggregates (25–100% sand replacement) as a viable route toward low-carbon and climate-resilient construction. Cork addition markedly modifies rheological behavior—reducing dynamic yield stress from 387 to 55 Pa and plastic viscosity from 10.8 to 4.8 Pa·s. It also delays the development of static yield stress, highlighting the need for admixture optimization to maintain buildability. Mercury intrusion porosimetry reveals a sharp increase in total porosity (from 4.7% to 51.1%) and the formation of large capillary voids, resulting in reduced mechanical strength. Despite this, cork incorporation significantly mitigates mechanical anisotropy: circular statistical analysis of macro-pore orientation shows that cork disrupts the horizontal pore alignment induced by printing, promoting a more isotropic internal structure and uniform stress distribution. Thermal performance is substantially improved, with thermal conductivity reduced by 67% (from 0.91 to 0.30 W/m·K) and specific heat capacity increased from 0.8 to 1.33 J/g·°C, enhancing the material’s thermal inertia. Sustainability assessments further demonstrate the material’s promise: at ≥ 75% cork replacement, the mixture becomes carbon-negative (−40.07 kg CO₂-eq/(m³·MPa)). A building-scale simulation conducted for a cold-climate context (Nome, Alaska) reveals 13.2–35.1% annual energy savings and operational CO₂ reductions of up to 15,203 kg compared to conventional concrete systems. These findings validate recycled cork–based 3D printable concrete as a multifunctional solution integrating rheological tunability, structural reliability, thermal buffering, and net-negative carbon performance.