Rice-Husk Shredding as a Means of Increasing the Long-Term Mechanical Properties of Earthen Mixtures for 3D Printing.

This paper is part of a study on earthen mixtures for the 3D printing of buildings. To meet the ever increasing environmental needs, the focus of the paper is on a particular type of biocomposite for the stabilization of earthen mixtures-the rice-husk-lime biocomposite-and on how to enhance its effect on the long-term mechanical properties of the hardened product. Assuming that the shredding of the vegetable fiber is precisely one of the possible ways to improve the mechanical properties, we compared the results of uniaxial compression tests performed on cubic specimens, made with both shredded and unaltered vegetable fiber, for three curing periods. The results show that the hardened earthen mixture is not a brittle material, in the strict sense, because it exhibits some peculiar behaviors that are anomalous for a brittle material. However, being a "designable" material, its properties can be varied with a certain flexibility in order to become as close as possible to the desired ones. One of the peculiar properties of the hardened earthen mixture deserves further investigation, rather than corrections. This is the vulcanization that occurs (in a completely natural way) over the long term, thanks to the mineralization of the vegetable fiber by the carbonation of the lime.

Mechanical Properties of a 3D-Printed Wall Segment Made with an Earthen Mixture.

This study provides a contribution to the research field of 3D-printed earthen buildings, focusing, for the first time, on the load-bearing capacity of these structures. The study involves the entire production and testing process of the earthen elements, from the design, to the preparation of the mixture and the 3D printing, up to the uniaxial compression test on a wall segment. The results indicate that 3D-printed earthen elements have a compressive strength of 2.32 MPa, comparable to that of rammed earth structures. The experimental data also made it possible to draw conclusions on the action of the infill, which seems to have the function of stopping the propagation of cracks. This has a positive effect on the overall behavior of 3D-printed earthen elements, since it avoids the onset of dilative behavior in the final stages of the load test and maintains ultimate load values higher than 50% of the maximum load.