Inline quantification of extrudability of cementitious materials for digital construction

Digital construction (DC) is a new process, and hence, no standard experimental methods for process-specific material characterization are as yet available. This article proposes a methodology for characterizing the extrudability of cement-based materials for DC, both quantitatively and inline. A 3D-printing test device was used for this purpose, which enabled the elimination of most artefacts in the characterization of materials. Unit extrusion energy UEE, defined as the energy consumed per extruded unit volume, was used as the measure of extrudability, lower UEE implying higher extrudability. The results obtained using the proposed approach were compared with results of a simple ram-extruder, slump-flow and viscometer tests. Two fine-grained concrete mixtures under investigation, one with ordinary sand and one with very fine sand, having respective yield stresses of 306.2 Pa and 642.7 Pa, were characterized. They showed a significant difference in their extrudability: the UEE needed in the case of material with finer sand was 1.62 times higher than that of the mixture with coarser sand. Interestingly, average ram extrusion force for the finer mixture was much lower than that of the coarser mix, underlining the challenges in material characterization and the need to consider the possible artefacts of various testing methods. Comparative analyses substantiated the significance of the proposed inline extrudability quantification method for DC.