Non-destructive evaluation for the unbonded interlayer of 3D printed concrete

3D concrete printing has been widely adopted for fabricating structures without formwork owing to its benefits with an automatic construction and reducing construction waste. To fabricate optimized products, control of the printing process is essential, including the precise management of mechanical components and the use of high-quality materials. Various non-destructive evaluation can be employed to control the deposited filaments and produce high-quality products. This study aims to evaluate the unbonded interlayer between 3D printed concrete layers using electrical resistivity measurement before concrete hardening. The Wenner and square arrays based on the four-electrodes method were designed to assess the unbonded interlayer as soon as concrete layers are printed. A rectangular shape of layered samples with dimensions of 320 mm x 320 mm x 200 mm (ten-layers) are additively manufactured by the 3D printing system. Three different interlayer conditions between fifth and sixth layers is considered to evaluate the defective interlayers using electrical resistivity measurements. The measured electrical resistivity of sample’s length shows that the increased unbonded area between interlayers results in the increased electrical resistivity. The unbonded interlayer is strongly associated with on reduced flexural strength. This finding can represent that evaluating printed layers using electrical resistivity measurements is necessary to obtain high-quality products. The efficient manufacturing consumption time or structural stable, may be decreased to evaluate the defect of the interlayer at the early age concrete before its hardening state.