Advanced measurement techniques for plastic shrinkage and cracking in 3D-printed concrete utilising distributed optical fiber sensor

Due to the absence of formwork, 3D-printed concrete (3DPC) suffers from high plastic shrinkage and cracking risks at an early age. Compared with conventional cast concrete, 3DPC has a unique layered structure and irregular shape of elements, which causes the uneven shrinkage strains distribution that cannot be fully characterised by traditional methods. This study developed a novel method that aims to measure the plastic shrinkage of 3DPC and monitor the cracking risks in the early stage with the aid of distributed optical fiber sensors (DOFS). The feasibility of using the optical frequency domain reflectometry to measure the plastic shrinkage of 3DPC was experimentally studied, and the coefficient of variation of the results was between 6.99% and 8.05%. The accuracy of the plastic shrinkage obtained by the DOFS method was validated by comparing with the image processing method. Besides, this advanced measurement technique provided multiple functions, which could not only detect the location, width, and development of cracks, but also predict the occurrence of cracks. The utilisation of DOFS method to measure the strains of 3DPC at various positions along the fiber direction has good potential to explore the short and long-term properties of 3DPC and monitor the structural health of 3DPC structures.