Influence of Time Gap on the Buildability of Cement Mixtures Designed for 3D Printing

Abstract

This study provides novel insights into the nuanced impact of time gaps on the buildability of cement mixtures within the 3D printing process. In contrast to studies predominantly focused on rheological properties, this research addresses essential factors such as printed structure size, which inevitably affect the temporal intervals between layer depositions and consequently shape the buildability outcome. The investigation encompasses cement mixtures with diverse water-to-cement ratios (ranging from 0.26 to 0.36), varied setting accelerator concentrations (1.0 to 2.0 wt.%), and superplasticizer contents (0.25 and 0.5 wt.%), all explored across different time gaps (ranging from 5 to 25 min). The evaluation of buildability involves a meticulous assessment of the deformation of the bottom layer induced by adjacent layers. The findings underscore the substantial role played by chemical admixtures in fine-tuning rheological properties specific to each time gap, thereby influencing the size of the printed structure. The impact of the accelerator admixture is evident in its ability to reduce the minimum time gap required for optimal buildability while the superplasticizer emerges as a key player in enhancing fluidity without compromising the load-bearing capacity of the printed structures. To predict buildability for a given time gap, the study leverages the results of spreading diameter from the flow table test and the setting time from the Vicat test. Lastly, this study extends its scope to unveil insights into the intricate interplay between time gap and printing speed for 3D printed real-scale constructions by examining the relationship among these parameters across constructions with diverse built areas.