The Synergistic Effect of Ester-Ether Copolymerization Thixo-Tropic Superplasticizer and Nano-Clay on the Buildability of 3D Printable Cementitious Materials.

Yu Wang,Tinghong Pan,Kangting Yin,Yaqing Jiang

doi:10.3390/ma14164622

Abstract

The shape retention ability of materials deposited layer by layer is called buildability, which is an indispensable performance parameter for successful 3D printable cementitious materials (3DPC). This study investigated the synergistic effect of nano-clay (NC) and thixotropic superplasticizer (TP) on the buildability of 3DPC. The rheological parameters and static yield stress are characterized by the rheology testing, the green strength is measured by a self-made pressure tester, and the fluidity is tested by flow table. Results indicate that NC significantly increases the growth rate of static yield stress and green strength and TP can improve the initial rheological parameters and fluidity, which ensures the initial stiffness and workability of printed materials. The mixture with 7‰ (by mass of cementitious materials) NC and 3‰ TP obtains excellent extrudability and buildability, due to the synergistic effect of NC and TP. Based on the rheology testing and specific printing experiments, a printable window with 1.0 Pa/s~2.0 Pa/s of the rate of static yield stress evolution over time (RST) or 170 mm~200 mm of fluidity is established. This work provides theorical support for the control and evaluation of rheological properties in 3DPC.

Highlights

In traditional casting techniques, concrete products are formed in molds or subtracted by milling, while 3D printing of cementitious materials is an additive manufacturing approach to build 3D printed constructs through layer deposition and stacking so that the automated process can be finished from digital models [1,2,3,4]
There is an inevitable relationship between build-up ability and green strength of fresh mortar, which can be used as an evaluation method for characterizing the buildability. 3D printing is a dynamic phenomenon, a printable window time must be established by studying the properties over time of printed materials
It is found that the benchmark mortar collapses without additional load after demolding and the green strength developed slowly over time, it is not able to meet the construction accumulation requirements of printed mortar after being extruded from the nozzle, while the addition of thixotropic superplasticizer (TP) and NC significantly increased the green strength of materials

Summary

Introduction

Concrete products are formed in molds or subtracted by milling, while 3D printing of cementitious materials is an additive manufacturing approach to build 3D printed constructs through layer deposition and stacking so that the automated process can be finished from digital models [1,2,3,4]. During the accumulation of 3D printable cementitious materials (3DPC) layer by layer, the first layer needs to support its own weight and later the successive deposited layers by depending on the static yield stress which changes with time. The buildability of 3DPC is related to the capacity of printing several continuous layers, i.e., the materials should have suitable fluidity to avoid the fracture of printed filaments due to the inability to be continuously extruded [10,11]. Based on the assumption that the growth of static yield stress has a linear relationship with time during the hydration induction period, Yuan et al [15] improved the thixotropy of fresh mortar and established the linear equation slope to evaluate and predict the 3DPC buildability

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Results

Conclusion