Layer interface strength for 3D-printing of earth-based materials

Abstract

It is becoming more and more attractive to move from a more manual construction technique, as it is done nowadays with earth-based materials to a digital one. Earth structures are very labor-intensive and time- consuming, which means they cost a lot of money. Therefore, the application of additive manufacturing technologies has a great potential of advantages in the construction industry, such as economic, social and design freedom factors. Most of today’s research studies have been performed with Ordinary Portland Cement (OPC)-based mortars and concretes. On this account, the objective of this bachelor project is to compare the hardening and strengthening properties regarding 3D printed constructions of an eco- friendly and more sustainable earth composite admixed with trass, gypsum and lime (TGL) to stabilised earth with OPC. The results prove that the addition of a binder does accelerate the curing process of the compounds significantly. High intakes of flexion strength for the time delayed cast of moulds were observed. Regarding the phenomenon of cold joints, the results from the flexural bending attempts don’t show an increase in layer interface strength for the samples with binder compared to the reference without binder. Still these results show, that a faster layer-by-layer deposition is possible due to the presence a binder. Based on the study of the alternative binder TGL, it was found that TGL in small quantities does not have a considerable influence on the curing process and the strength behavior of the compound. However, for a TGL content of 20% comparable values in mechanical properties (flexural and compressive strength) were obtained as for 7% cement addition. Which would make TGL a competitive binder to OPC. Furthermore, the curing properties of TGL can be used as an advantage for 3D printing, as there is no immediate curing as with OPC and thus could optimize the printing process. Moreover this could counteract the problem of cold joints.