Durability Evaluation of Soil-Geopolymer Based Composites for 3D Printing Applications in Geotechnical Engineering (2026-03)¶

This study explores the feasibility of utilizing geomaterials for extrusion-based 3D printing applications in geotechnical engineering and evaluates the durability of the developed novel soil-geopolymer composites. Two different types of locally available soils, i.e., poorly graded sand and clayey sand, were blended with ground granulated blast-furnace slag and Class-F fly ash, activated by alkali solutions, to develop 3D printable mixes. Due to the addition of soils to geopolymer, the developed mixes are expected to possess dual soil-concrete characteristics. Hence, durability was assessed under wet-dry and freeze-thaw cycles following both soil and concrete testing protocols by measuring the mass loss, volume change, and unconfined compressive strength to fully understand the behaviors of these novel mixes. Nondestructive test such as ultrasonic pulse velocity (UPV) test was also used to measure the changes of internal structure of the materials throughout the durability cycles. The results showed that the compressive strengths reached 13 MPa for sandy soil composites and 11 MPa for clayey sand soil composites at 28 days, confirming their structural viability. Moreover, the developed mixes showed good resistance to both freeze-thaw and wet-dry conditions. Most of the developed composites exhibited negligible mass and volume changes under wet-dry conditions, with a slight strength increase over the eight cycles of wetting and drying. Whereas for freeze-thaw tests, the test following concrete protocol resulted in the greatest damage with up to 8% volume loss and noticeable strength reduction. UPV results remained largely stable, suggesting limited internal matrix alteration despite visible surface damage. Printing trials of both mixes were also conducted, and the results demonstrated that sandy soil mixes enabled smooth extrusion and successful 3D-printed models, while clay-rich mixes showed excessive cohesion, nozzle clogging, and difficulty in printing, indicating the importance of soil types in 3D printable soil-geopolymer composite designs. Overall, this study highlights the novelty of combining durability evaluation with soil-based geopolymer composites for 3D printing, providing both experimental evidence and practical pathways toward sustainable printable geomaterials.