Development of an ordinary portland cement-free 3D-printable loess-based material: Mix design, printability and performance

This study develops an ordinary Portland cement (OPC)-free, 3D-printable loess-based material through an integrated formulation–process–performance approach. Thirteen modified mixtures (M1–M13) were designed using a multi-component calcium-bearing binder, graded aggregates, biopolymer modifiers, and treated straw fibers. Fresh-state performance was assessed through flow-table measurements, comparative rotational viscometry, and direct buildability tests, while mechanical properties were evaluated through compressive testing. Complementary SEM–EDS, XRD, XRF, TG/DTG, and mercury intrusion porosimetry (MIP) analyses were conducted to characterize the traditional control (TRA) and optimized mixture M13. Among the thirteen modified formulations, M13 achieved the highest mean 14-day compressive strength of 1.064 ± 0.064 MPa. It also exhibited the highest buildability among the four directly tested formulations, sustaining 7.67 ± 0.58 stable layers. MIP revealed lower mercury-accessible porosity in M13 (32.30%) than in TRA (38.56%), indicating a refined accessible pore-throat structure. In the preliminary 28-day printing validation, the recorded compressive strength of printed M13 was approximately 3.9% lower than that of its cast counterpart, while the printed element exhibited a 2.5% height reduction relative to its nominal initial dimension. These findings demonstrate that coordinated formulation design can improve the balance between mechanical performance and layer-stacking capacity. The study provides a process-oriented experimental framework for developing OPC-free printable earthen materials, while further durability and interface-performance assessments remain necessary.