Page 43 - MSAM-1-3

Optimization of chemical admixtures for 3DCP

Materials Science in Additive Manufacturing

the accelerator was then added, and the mixing process 3.3. Printability test
continued for 1 min in speed II (113 rpm). Finally, a printing test was conducted to investigate
Rheological properties of mixed materials, including static/ the printability of designed mixture. As shown in
dynamic yield stress and plastic viscosity, were characterized Figure 5, a gantry printer with a 1.2 m × 1.2 m × 1.0 m
via Viskomat XL. The six-blade vane probe and cage are used (L × W × H) printing volume was used to print
for rheological test to avoid slippage of cement paste. Both specimens. The dimension of nozzle opening was 30 mm
the diameter and the height of this vane probe are 69 mm, × 10 mm. Nozzle travel speed and pumping speed are
and the gap between probe and cage, and the bottoms of 2,000 mm/min and 650 rpm, respectively. The standoff
probe and barrel are both 40 mm. During the rheological distance was 30 mm. 3D model used in the printing test
test, the speed of rheometer increased linearly from 0 rpm is shown in Figure 6.
to 60 rpm in 5 min. Afterward, the speed decreased linearly
to 0 rpm in another 5 min as shown in Figure 3. The typical
test result of rheological properties is plotted in Figure 4.
Then the static/dynamic yield stress and plastic viscosity
can be computed by Equation VII [ :
11]
2
2
4RR lk 4RR l R
2
2
1 2 1 2 d ln 1 (VII)
R 2 2 R 1 2 2 R 2 2 R 1 2 R 2
Where Γ (N·m) is the torque, ω (rad/s) is the rotational
2
speed of outer barrel, l (m) and R (m) are the length and
1
radius of the probe, respectively, and R (m) is the radius of
2
the outer barrel. Thixotropy value is measured by the area
of hysteresis loop [8,15,35] in Figure 4.
Table 1. Chemical composition of FA and OPC
Formula Concentration/%
FA OPC Figure 3. Rheological testing programs.
SiO 58.59 24.27
2
Al O 30.44 4.56
2 3
Fe O 4.66 3.95
2 3
TiO 2 2.02 0.55
K O 1.51 0.61
2
CaO 1.21 62.2
MgO 0.776 3.34
P O 0.531 0.15
2 5
Na O - 0.21
2
SO 3 0.0914 -
ZrO 0.04 -
2
MnO 0.0351 -
Cr O 0.027 -
2 3
CuO 0.0254 -
ZnO 0.0229 -
OPC: Ordinary Portland cement, FA: Fly ash Figure 4. The typical test results of rheology.
Table 2. Mixture proportion

OPC (g) Sand (g) W (g) FA (g) SF (g) Retarder (g) Accelerator (g) Superplasticizer (g)
1356 1729 1024 2034 68 4.47–15.9 4.47–15.9 2.24–7.93

Volume 1 Issue 3 (2022) 4 https://doi.org/10.18063/msam.v1i3.16