Article
Experimental Study on Time-Dependent Changes in
Rheological Properties and Flow Rate of 3D Concrete
Printing Materials
Hojae Lee * , Eun-A Seo, Won-Woo Kim and Jae-Heum Moon
Citation: Lee, H.; Seo, E.-A.; Kim,
W.-W.; Moon, J.-H. Experimental
Study on Time-Dependent Changes
in Rheological Properties and Flow
Rate of 3D Concrete Printing
Materials. Materials 2021, 14, 6278.
https://doi.org/10.3390/ma14216278
Academic Editors: Ludwig Cardon
and Clemens Holzer
Received: 13 September 2021
Accepted: 12 October 2021
Published: 21 October 2021
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4.0/).
Department of Structural Engineering, Korea Institute of Civil Engineering and Building Technology
Daehwa-Dong, Goyang-si 10223, Gyeonggi-do, Korea; sea0524@kict.re.kr (E.-A.S.);
kimwonwoo@kict.re.kr (W.-W.K.); mjh4190@kict.re.kr (J.-H.M.)
* Correspondence: h.lee@kict.re.kr; Tel.: +82-31-910-0390
Abstract:
Three-dimensional concrete printing (3DCP) materials require a relatively low water-to-
binder ratio (W/B) of 0.3 or less to ensure their buildability and flow properties are sufficiently
maintained after mixing. In this study, the rheological properties of 3DCP materials with W/B 0.28
were evaluated up to 60 min after mixing, and the yield stress and plastic viscosity were analyzed
over time. A gradual decrease in flow rate with time was observed during the transport of 200 kg
of material per batch through a 20 m hose. To examine the time-dependent changes in flow rate
and layer volume, a 2200 mm
×
1000 mm test specimen was printed. The dependence of the layer
width over time during the printing process was measured and analyzed. The experimental analyses
showed that the flow rate and layer volume of the 3DCP material gradually decreased with time
after mixing, which was correlated with the rheological properties.
Keywords:
3D concrete printing; ordinary Portland cement; shear stress; plastic viscosity;
pumpability
1. Introduction
Three-dimensional concrete printing (3DCP) technology has recently been employed
in successful construction attempts, including a two-story building in the UAE by Apis
Cor in 2019 and pedestrian bridges by TU Eindhoven in the Netherlands and Tsinghua
University in China. These examples have demonstrated the tangible progress that 3DCP
has undergone in the nearly 20 years since Contour Crafting was announced by the
University of Southern California in the early 2000s [
1
]. The recent development of 3D
printing technology has grown to encompass the areas of multi-story buildings, horizontal
structural members, and other civil engineering applications, and the related success stories
have been promoted in many public media outlets. As a result, 3DCP has been positioned
as a promising future construction technology.
Current 3DCP processes commonly involve additive layering with material extrusion
using cementitious binder-based (mainly OPC—ordinary Portland cement) cement paste,
mortar, and concrete as the main materials as listed (Table 1). Because cementitious binders
undergo setting and hardening with time after hydration, the material must retain a
flowability appropriate for 3DCP for a sufficient pumpability until extrusion. Nevertheless,
to ensure buildability of layers and printing member, the yield stress and plastic viscosity
of the 3DCP material were increased in a previous study [
2
] because these properties aid
in supporting the weight of successively added layers and maintaining the shape of the
structure.
Materials 2021, 14, 6278. https://doi.org/10.3390/ma14216278 https://www.mdpi.com/journal/materials
