Effect of Micro/Nano Reinforcements on Mechanical Properties of 3D Printed Cementitious Materials

Abstract

This study investigates the effects of micro/nano-reinforcements on the fresh and hardened properties of 3D-printed cementitious materials (3DPC), with a particular focus on a sustainable and cost-effective graphene derivative, namely date syrup-based graphene-coated sand hybrid (D-GSH). D-GSH is synthesized using natural date syrup and dune sand via pyrolysis process without adding any toxic chemicals. The performance of D-GSH in 3DPC was compared with conventional additives such as carbon nanotubes (CNTs) and silica fume (SF). To evaluate the influence of D-GSH, CNTs, and SF on the performance of 3DPC, comprehensive experimental methods were conducted. Initially, printable mix proportions were obtained by varying the contents of cementitious materials and validated through successful single- and double-layer prints without extruder blockage. Fresh-state properties were tested by examining printing quality, buildability, open-time, and rheology to assess printability and extrusion behavior of 3DPC. Subsequently, hardened-state properties were assessed through compressive and flexural strength mechanical testing. Moreover, durability tests such as water absorption, permeable voids, shrinkage, and resistance to fire, acid and carbonation were performed to examine the long-term resilience of 3DPC.
The addition of 0.14% D-GSH (by weight of cement) led to significant enhancements in the performance of 3DPC. Fresh-state properties were notably improved, with buildability increasing by 108% compared to a mix containing 5% SF and exceeding the 0.2% CNTs mix by 20%. Regarding mechanical properties, the addition of 0.14% D-GSH enhanced compressive strength, elastic modulus, and flexural strength by 62%, 40%, and 118%, respectively, compared with a mix containing 5% SF. Interestingly, despite its lower dosage, D-GSH outperformed CNTs in flexural strength by 10% and showed comparable compressive strength with improved ductility. Durability tests further highlighted the superior performance of D-GSH compared with CNTs and SF. D-GSH reduced water absorption and permeable voids to 7.8% and 12.9%, respectively, when compared to a mix containing SF. Furthermore, D-GSH demonstrated higher resilience to shrinkage, acid attack, fire exposure, and carbonation compared to CNTs and SF. These improvements are attributed to the ability of D-GSH to bridge nano-cracks, refine pores, and bond with the hydration products of the cement matrix. Notably, these enhancements were achieved with a lower dosage, i.e., 0.14% D-GSH compared to 0.2% CNTs, highlighting its superior efficiency as a sustainable additive. Overall, this study demonstrates the potential of both D-GSH and CNTs in enhancing the performance of 3DPC, with D-GSH emerging as a more efficient alternative, delivering better performance and contributing to sustainable additive manufacturing in construction.

Date of Award	2025
Original language	American English
Supervisor	Tae Yeon Kim (Supervisor)