Abstract
Interfaces between layers in 3D-printed elements produced by extrusion-based material deposition were investigated on both macro- and micro-scales. On the macro-scale, compression and flexural tests were performed on two 3D-printable cement-based compositions (3PCs), namely Mixtures C1 (with Portland cement as sole binder) and C2 (containing pozzolanic additives) at testing ages of 1 day and 28 days. The influences of binder composition and time interval between layers on layer-interface strength were critically analyzed. The investigated time intervals were 2 min, 10 min and 1 day. The investigations revealed that Mixture C2 exhibited lower degrees of anisotropy and heterogeneity as well as superior mechanical performance in comparison to Mixture 1. In particular, Mixture C2 showed a less pronounced (below 25%) decrease in interface bond strength as observed in flexural tests for all time intervals under investigation. In contrast, the decrease in flexural strength measured for C1 specimens amounted to over 90% due to the higher porosity at the interfaces of the printed concrete layers. Microscopic observations supported the findings of the macroscopic investigations. SEM images also delivered additional information on morphology of interfacial defects as well as “self-healing”.
Highlights
Digital concrete construction (DC) in general and 3D-printing in particular make speedy, economic, formwork-free construction possible and enable flexible architectural design with higher construction safety [1], [2]
A Portland cement (PC) with rapid-hardening and high early strength properties, CEM I 52.5R according to EN 197-1 [28], and a Class F fly ash according to ASTM C618-12a [29] were used as dry binder components
In the article at hand, first, the mechanical properties of 3D-printed, fine-grained concrete specimens were investigated with respect to the effect of interface quality between individual layers, accompanied by microscopic analysis, of the interface areas
Summary
Digital concrete construction (DC) in general and 3D-printing in particular make speedy, economic, formwork-free construction possible and enable flexible architectural design with higher construction safety [1], [2]. 3D-printing techniques with concrete have great potential, many technological issues are still open and need to be investigated scientifically. Weak interface strengths or the occurrence of so-called “cold joints” between printed layers is one such issue. Due to the inherent “layered” nature of 3D-printed elements, layer-to-layer interfaces are unavoidable. In many instances they are the weakest links in the entire structure; see Figure 1. The weakest links induce a pronounced anisotropy and negatively affect mechanical performance, and the durability of 3D-printed elements [3]
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