Effect of the structuration rate on dimensional stability and mechanical performance of 3D printed mortars

Digital concrete fabrication is a novel construction technique in which structural elements are built layer by layer without the use of formwork. This technology has introduced new challenges in materials engineering. More emphasis lies on the structuration behavior of cement-based materials. Concrete is designed to achieve adapted workability to flow during the pumping phase. It also requires proper build-up and stiffness to retain its shape after extrusion and sustain its own weight and, subsequently, the weight of successive layers. A high degree of structuration is recommended to ensure high printing quality. However, this may adversely affect the performance of the multi-layer printing process. In the present study, an experimental program was carried out to evaluate the impact of structuration rate on the dimensional stability and mechanical properties of the printed element at both early age and long term, respectively. Four different mixtures with various structuration rates were designed and printed. In the fresh state, variations in the layer’s height and width were recorded to evaluate the dimensional stability of the printed structure. On the other hand, several specimens were cut out of the freshly printed elements for mechanical tests. The compression and flexural tests were conducted after 7 and 28 days of moist-curing. The obtained results showed that there exists an optimum rate of structuration above which the quality of the bonding interface is compromised, generating losses in mechanical properties. Under this threshold, anisotropic behavior dominates, leading to low dimensional stability.