Page 21 - Open-Access-Sep-2019

TECHNICAL PAPER

Construction and demolition recycling wastes have potential
for use in the powder-based 3DP technique. For example,
Kandasami [36] stated that the construction industry in India
produces 50 million tonnes of waste and that 50% of that
waste could be recycled. After crushing waste to powder and
small particles, this could be utilised in a powder-based 3DP
technique for construction applications. The recycled wastes are
easy to convert into powder, which can then be used in a printer.
Later, the print command could replicate thousands of objects
according to the CAD model. In future, as technology advances,
the powder-based 3DP technique could be developed into a
single machine that not only works such as a crusher but also
Figure 11: Surface roughness profile and images captured of the surface
of printed cement mortar at 20×, 50×, and 100×; the bottom image uses the powders to print objects. It is also crucial to conduct
shows the roughness profile compared with the mean line. further investigations of printed structures using chopped strand
fibre reinforcement. The fibre could improve the mechanical
There is a strong relationship between the surface roughness properties and material characterisation of the printed parts.
(Ra) of the powder materials and the contact angle (wettability)
of the liquid droplet on the surface of the powder. Two situations 4. coNclUsIoNs
should be taken into account with respect to surface roughness, To sum up, 3DP technology is emerging as an advanced
namely, if the binder droplet leaves a groove on the surface or technique to construct highly precise and complicated
if air pockets are left between the droplet and the surface [33] . geometries, which are conventionally difficult to fabricate. This
Figure 12 shows the different surface roughness of embedded study investigated different curing temperature effects on the
powder particles on the build chamber of the 3DP for CP and ZP printed mortar specimens. Compressive strength tests were
151 powders. The original powder (ZP 151) has a uniform particle also conducted on sets of different sized cubic specimens, and
distribution on the surface, whereas CP powder has uneven flexural strength tests were performed on one set of rectangular
particle distribution on the surface. prism specimens. The results were as follows:
• The larger sized specimens had higher mechanical
strength, when the size of the specimen increased from
20x20×20 mm to 50x50×50 mm, it resulted in an increase in
compressive strength of 10%;
• Optimum compressive strength and flexural strength can be
achieved by using a post-processing curing process at an
elevated temperature of 80°C;
• Curing specimens at 90°C resulted in cracks on the surface
of the printed specimens;
• The printed mortar specimens had a rougher surface quality
Figure 12: Surface roughness profile of powder-bed on the build than the original material (gypsum); and
chamber for CP and ZP 151 materials.
• The surface roughness quality of the printed specimens was
related to the embedded powder distribution on the build
The modified powder can be improved by (10-40%), ensuring
better powder formulation and more environmentally friendly chamber and high surface roughness on the build chamber
results, by utilising fly ash as a replacement for OPC and CAC. resulted in a high surface roughness profile on the printed
For that purpose, it is vital to conduct further investigations to specimens.
develop a modified powder and reduce voids among powder Further study is required on inkjet 3DP, specifically on post-
particles. According to the study by Chindaprasirt and Rukzon processing media and infiltration. Ideally, this future work can
[35] , the fine fly ash, with a median size of (4.9 µm), yielded focus on broader applications for construction purposes, such as
positive results when used in mortar. They observed that a 10% an investigation of larger-scale prints in real-life especially with
replacement of fly ash to cement in the mortar mixture improved recycled material.
compressive strength and reduced apparent porosity. Therefore,
using a low percentage of fly ash could reduce the apparent aCknowlEDgEMEntS
porosity in printed specimens and lead to an improvement in The authors acknowledge the support of UTS’s ProtoSpace and
the mechanical strength of the printed scaffold. the Civil Engineering laboratory.

72 The IndIan ConCreTe Journal | SepTember 2019