Nondestructive testing techniques for investigating mechanical property and porosity disparities in extrusion 3D printed concrete

Three Dimensional Concrete printing (3DCP) stands at the forefront of modern construction methodologies, also named additive manufacturing, offering unparalleled time, cost, and labour savings compared to conventional approaches. The evaluation of fresh state parameters like extrudability and buildability through a specialised concrete extruder, combined with a methodical layer-by-layer deposition, ensures structural stability by precisely strengthening each layer. Mechanical strength evaluations highlight the printed material’s anisotropic nature, revealing extreme reductions of Fy = 27.94%, Fx = 19.07%, and Fy = 16.33% in compression, flexural, and split tensile strengths, respectively, compared to cast specimens. This emphasises the importance of direction-specific mechanical testing in understanding material behaviour completely. Non-destructive testing (NDT) methods, like Ultrasonic Pulse Velocity (UPV) testing, are crucial for the qualitative assessment of the integrity and mechanical strength of concrete structures, including both printed and cast specimens, by establishing a strong correlation with compressive strength without causing any damage. Limited research indicates that the microstructure of the material plays a significant role in its mechanical strength, particularly in printed specimens. This claim is reinforced by mercury intrusion porosimetry (MIP) results, which reveal that printed specimens have slightly higher overall porosity, concentrated between 1 µm and 0.1 µm, while cast specimens show higher porosity in pores smaller than 0.1 µm.