3D Concrete Printing (3DCP) has emerged as a disruptive additive‑manufacturing technology that redefines on‑site concrete fabrication. By depositing material layer by layer directly from digital models, 3DCP eliminates conventional formwork, reduces labor requirements and material waste, and enables unprecedented geometric freedom [1]. Large‑scale demonstrations have validated the production of complex free‑form structures without auxiliary supports, highlighting the potential for novel architectural expressions [2].

Despite these advances, interlayer bonding remains a critical technical challenge. The time lapse between successive depositions creates so‑called “cold joints,” which can compromise interface strength if the underlying layer gains excessive stiffness. Empirical studies demonstrate that deposition interval, surface moisture and mix rheology are decisive factors governing interlayer adhesion [3]. To address this, researchers have optimized mixture designs—balancing extrudability and early‑age buildability via tailored admixtures and fibre reinforcement—and developed thixotropic‑based models to prescribe deposition rates that ensure each layer can reliably support the next [4][5].

Integrating conventional reinforcement into 3D‑printed elements poses another hurdle. While embedding steel bars remains cumbersome, alternative strategies—such as interlocking layer geometries or in‑situ mineralization at interfaces—have shown promising improvements in shear strength and cold‑joint “healing” [6]. Meanwhile, the absence of dedicated standards for layered, extrusion‑printed concrete creates regulatory uncertainty regarding anisotropic mechanical properties, long‑term durability and appropriate testing protocols. Nonetheless, pilot projects—from pedestrian bridges to residential buildings—are proceeding under experimental approvals, paving the regulatory path forward [7].

Sustainability considerations further motivate 3DCP development. By deploying material only where structurally and architecturally necessary—and eliminating formwork—waste reductions of up to 60 % and labor‑cost savings approaching 50 % have been reported. Moreover, compatibility with low‑clinker cements and geopolymers suggests possible lifecycle‑carbon reductions of 70–90 %, provided such mixes maintain printability and adequate performance [1][8].