A study on the effect of mixture constituents on washout resistance, mechanical, and transport properties in the context of underwater 3D concrete printing

Abstract

Underwater layered concrete depositions, such as those obtained using 3D printing, demonstrate washout resistance, which influences layer stability, transport properties, and inter-layer mechanical strength, thus impacting its final properties. This work first focuses on understanding the compositional effect of 3D printable mortars on their washout resistance. Conventional methods for assessing washout resistance of underwater concrete are ill-suited to 3D printable materials due to different mix designs and material deposition techniques. To address this, a new protocol considering layered deposition during 3D printing was developed to evaluate the washout resistance. Interrogation of the pore structure of the printed specimens (in air and underwater environment) via water absorption and sorptivity test further establishes the influence of washout on water transport properties. The study also investigates the impact of hydroxypropyl methylcellulose (HPMC) and polyvinyl alcohol (PVA) fiber dosages on mechanical properties, including compressive strength, interlayer split tensile strength, and flexural strength. Results indicate that HPMC addition significantly improves the washout resistance, whereas PVA fibers have detrimental effect. However, optimizing the PVA fiber dosage enhances both mechanical and water transport properties of underwater printed specimen via permeable void and capillary pore structure refinement.