EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Additive manufacturing, given its advantages, has developed strongly in many industrial sectors, particularly in the construction field. However, in this specific area of geomaterials, the cementitious material must meet demanding specifications to be printable. In a contradictory manner, it must be sufficiently fluid in the fresh state to facilitate pumping and extrusion but it must stiffen quickly to ensure the constructability and stability of the printed structures. In addition, the time gap between two consecutive layers must be long enough to ensure the stability of the deposited layers, but also short to avoid excessive drying which could compromise the quality of the interface. The mechanical characterization of this type of material is often carried out by means of conventional tests, mainly by compression testing. However, this technique provides access to a mechanical characteristic representative of the overall behavior of the material.

In this work, classical indentation tests applied at a micro scale allow a fine mechanical characterization of the two layers, independently of one another, and of the interface between the two consecutive layers of printed concrete. Accordingly, an indentation methodology is proposed to determine an absolute hardness number which is used to compare the hardness of the upper and lower layers. As a result, it was found that the upper layer is harder than the lower one. Also, a significant decrease in the hardness number at the interface was observed, proving that the interface is an area of weakness of printed material, as one would expect. In addition, the variation of a perpendicular hardness profile at the interface was studied as a function of the time gap between layers. We identify a criterion linked both to the distance according to which the hardness decreases and to the amplitude of the hardness between the core and the interface.