Ecological Design of Materials for Injection 3D Concrete Printing: The effect of Blast‐Furnace Slag and Limestone as Cement‐Substitutes on mechanical performance of nodes

Abstract

Injection 3D Concrete Printing (I3DCP) is a novel fabrication method in which fine‐grain concrete is injected into a non‐hardening carrier liquid (limestone powder suspension) where it remains stable. Reduced structural build‐up requirements in I3DCP offer potential for reducing cement content compared with extrusion‐based concrete printing. In this study, cement was systematically substituted with limestone powder (20 and 40 vol.‐%) and ground granulated blast‐furnace slag (ggbfs, 40 and 60 vol.‐%) in fine‐grain concrete. Changes in workability were minimized using superplasticiser. The effect of substitution on structural build‐up was quantified via yield stress evolution with slow penetration and in situ via slug test. In I3DCP these changes affect strand intersections (nodes). Here, the bond strength was investigated on hardened state specimens which were produced for three interlayer times (21 s, 5 min and 10 min). The mechanical tests of the nodes were performed by a custom transverse loading test. The results show that rheology dominates the bonding quality of printed nodes and therefore the slower reacting mixtures were beneficial for the node creation, especially at high time intervals. A reduction of concrete's yield stress from 4394 Pa to 1329 Pa resulted in a doubling of the nodes mechanical performance.