Three-dimensional concrete printing technology from a rheology perspective: a review

The flow and deformation of cement-based materials accompanies the full cycle of three-dimensional concrete printing (3DCP) and profoundly affects the quality of printed structures. Therefore, rheology is closely related to 3DCP technology. However, since printing materials undergo complex changes (from fluid to solid) during the entire process, it is extremely difficult to obtain the rheological parameters of the material accurately, which makes it difficult to characterise the material's properties and explore the rheological laws within the technical cycle. In this regard, this article starts from the perspective of rheology, systematically reviews the performance requirements of 3DCP technology for printing materials, critically discusses the existing methods for characterisation of material printability, including various conventional and unconventional methods, and clarifies the scope of application of each method. In addition, this article introduces several buildability models based on consideration of the time dependency of the printing material and indicates the direction for the optimisation of the performance of printing materials.