Mechanical and Durability Performance of 3D-Printed Concrete with Coarse Aggregates and Cold Joints (2025-07)¶

Three-dimensional (3D) construction printing technology has advanced significantly in recent years. Its application in building construction depends on a thorough understanding of the performance of printed materials. Hence, there is a growing need for precise mechanical and durability properties in printed concrete. Additionally, since this technology involves layer-by-layer printing, understanding how the printed materials perform at interlayer interfaces is crucial. Previous research primarily examined the mechanical properties of printed cement mortar with fine aggregates. There were limited studies on printed concrete with coarse aggregates and the behavior of cold joints. We investigated the mechanical and durability properties of 3D-printed concrete featuring coarse aggregates up to 10 mm in size through experimental tests. The compressive, flexural, and shear strength of the printed concrete was examined in three directions focusing on three treatments for cold joints. We also used nondestructive ultrasonic pulse velocity (UPV) to evaluate the quality of the printed concrete. The test results revealed that incorporating coarse aggregate improved bonding shear strength in cold joints. Additionally, using bonding agents at cold joints resulted an increase in overall compressive and flexural strength by approximately 10% when compared with cold joints treated with water alone. The experimental findings also showed that the 3D-printed concrete had an 11% increase in void ratio compared with the mold cast concrete. Practical Applications. The findings of this study offer practical guidance for construction professionals and researchers in the field of 3D construction printing (3DCP). While 3D-printing offers faster, cost-effective construction with less waste, a few challenges remain, such as weak interlayer interfaces, cold joints, anisotropic behaviors, durability, and lack of design standards. Incorporating coarse aggregates in 3D-printed concrete lowers construction costs. Therefore, this research investigated the impact of regular concrete with coarse aggregates (up to 10 mm) on the mechanical and durability properties of 3D-printed specimens. We demonstrated that coarse aggregates in 3DCP improve bonding shear strength at interlayer interfaces, which is critical to the structural integrity of printed components. Additionally, using bonding agents like concrete glue instead of water at cold joints increases compressive and flexural strength by approximately 10%. We highlighted the anisotropic behavior of printed concrete, which should be considered in the design of 3D-printed structures. Additionally, ultrasonic pulse velocity (UPV) proved effective for nondestructive quality assessment of printed components. These results support the development of design standards for printed structures, contributing to the creation of more durable and robust 3D-printed buildings and infrastructure.