Durability assessment and microstructural analysis of 3D printed concrete exposed to sulfuric acid environments

Abstract

Additive manufacturing techniques are being more adopted in the construction field, and they are rapidly developing. However, it is expected that layers superposition imposes several limitations on the performance of 3D printed structures. In this regard, an efficient concrete structure should not only present reliable mechanical performances, but also appropriate durability performance against weathering. This paper presents an experimental study aiming to compare 3D printed elements to casted ones on a macro and micro scale, as well as their resistance against sulfuric acid attacks. Herein, three different mortar mixes having different thixotropic properties were used, and two solution concentrations were employed, one containing 1% sulfuric acid and the other containing 3%. At first, a visual observation of the degraded samples and their mass loss were held. Then, a microstructural characterization was performed through mercury intrusion porosemetry (MIP) and scanning electron microscopy (SEM) analyses. Still, not any printed element has cracked at the interlayer level. Moreover, on a microscopic level, the MIP results showed that all samples of different compositions have an equal total porosity. However, the pore size distribution and their morphology largely differs between printed and non-printed specimens. The pore sizes are more spread in printed specimens. As for the SEM results, it can be clearly seen that no interface have revealed the formation of a weak plane that might even threaten the durability of the printed elements. Yet, a strong link between superposed layers has been developed, even when using materials having different rheological properties; and the overall specimen acted as a monolithic body without showing any signs of discontinuity or superposition effects.