Unbonded interlayer evaluation in freshly 3D printed concrete using electrical resistivity measurements

To achieve successful 3D concrete printing, meticulous control of the digital manufacturing process is essential, involving the precise management of mechanical components and the use of high-quality materials. Various evaluation methods have been employed in 3D printed concrete manufacturing to ensure high-quality products. This study proposes a nondestructive evaluation method for assessing unbonded interlayers during 3D printing. Two types of electrical resistivity measurements, Wenner and square array, were performed using four electrodes located in different layers. Eight square-shaped printed samples comprising ten layers were fabricated, including sound and unbonded cases along the directions of the interlayer length and depth. Based on the multi-points measurements, both nondestructive methods were compared to identify the optimal approach for unbonding the interlayer. The measured electrical resistivity was correlated with the obtained flexural strength, and a relationship between destructive and nondestructive results was proposed. Consequently, reproducible measurements of the electrical resistivity on the surface of layered concrete filaments allow the evaluation of interlayer bond properties in the freshly 3D printed concrete.