Microstructural mechanisms of chloride resistance enhancement in 3D printed concrete incorporating bamboo leaf ash

3D Printed Concrete (3DPC) offers advantages in automated construction and material efficiency, yet its layered interfaces and anisotropic pore structures present critical challenges to chloride ingress resistance in marine environments. This study investigates the incorporation of bamboo leaf ash (BLA), a byproduct of bamboo processing, into 3DPC to systematically evaluate its effects on microstructural evolution and chloride transport mechanisms. The study began with printability tests on 3DPC mixtures containing different BLA contents to determine suitable printable compositions. The mixtures satisfying printability standards were further analyzed via isothermal calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) to investigate hydration behaviors under the effect of BLA addition. Subsequently, accelerated chloride penetration test (ACPT) and mercury intrusion porosimetry (MIP) were conducted on the printed specimens to investigate chloride transportability and pore structure. In order to research chloride combination, nuclear magnetic resonance (NMR) was applied to the specimens. Results show that BLA promotes the buildability of 3DPC but reduces extrudability and open time, and an optimal BLA dosage range was identified based on printability results. BLA also delays early hydration yet improves long-term strength and decreases total porosity. BLA significantly decreases chloride migration rate and steady-state permeability, providing a moderate increase in chemical chloride binding and a pronounced enhancement in physical adsorption. The characteristic flat pore geometry of 3DPC further amplifies the contribution of physical binding. Overall, the combined test results demonstrate that BLA refines the pore structure, modifies hydration development, and enhances chloride binding, thereby effectively improving the chloride ingress resistance and durability of 3DPC in marine environments.