writes copy 26 May 2020

3D Printing in Construction: Cementitious Materials Fiber Reinforced Mortar

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Pshtiwan Nasruldeen Shakor recently submitted a thesis, '˜Investigation of Cementitious Materials and Fibre Reinforced Mortar in 3D Printing,' to the School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, at the University of Technology Sydney.

Continuing the trend for exploring the benefits of 3D printing in the construction industry, Shakor highlights features like greater speed, affordability, and latitude in design; still, however, the author states that the construction industry remains '˜far behind in the development of practical 3D printing machines.'

Schematic illustration of powder-based 3D printer with relationship between flowability, wettability, powder-bed porosity and porosity in the specimen.

Researching concrete and mortar in 3D printing, Shakor points out that traditionally, concrete casting to create molds is time-consuming and expensive'”resulting in many standardized elements.

'œThis method has consequences for repeated and over-dimensioned elements. The lack of freedom in form is another restraint. Despite these disadvantages, the rationalization of the construction process has resulted in very efficient reinforced structural members,' states Shakor.

Challenges persist concerning cost and wasted material during production'”especially when molds cannot be reused.

'œOverconstructed members in the production process are another limitation,' says Shakor.

'œMany freeform elements are cast in concrete in-situ, although the quality of cast-in-place concrete is difficult to control (Elhag et al. 2008). Therefore, high-performance concrete members are prepared in controlled environments. These precast members are part of a standardized building system, because of limitations in the size of the products that have to be transported later.'

Challenges arise in 3D printing for construction also because there simply are not that many materials available; also, due to the limitations of many 3D printers, printing on the larger scale can be difficult when needed.

Shakor discusses the fact that WinSun, building large construction parts, uses a robotic arm in accompaniment with 3D printers'”and uses a unique mixture of materials:

'œMix design and the use of coarse aggregates is another challenge for 3D printing of concrete. For instance, the WinSun company used only fine cementitious materials without coarse aggregate in its 3D printing application.'

Comparison of additive manufacturing technologies in the construction field.

While a variety of different methods are used for 3D printing in construction, the main comparisons include performance according to resolution, speed in production, and the properties of materials being used.

'œOne of the limitations of inkjet printing is the high porosity which makes the sample more fragile and permeable (i.e. water will easily pass through it),' stated Shakor. 'œTherefore, extra post-processing is required, such as curing with heat or with pressurized water steam (Dikshit et al. 2018).'

Mix proportion of the concrete used by Malaeb et al. (2015)

In delivery systems for 3D printing with concrete or mortar, pumpability and shapeability of the printed objects is key. The author explored the following types of systems:

  • Adapted auger extruder
  • Peristaltic pump
  • Progressive cavity pumps

Resultant Print of successful print yielding a stable mortar and decent slump slurry. Issues with the auger delivery struggling to consistently push out materials.

Printed cement mortar using a peristaltic pump with a 7.9mm diameter.

Product of the progressive cavity pump using a 20 mm circular nozzle.

WinSun is brought up again in regard to larger-scale printing, however, Shakor points out that they have seen many challenges during their work due to '˜off-site construction' parts, issues with brittleness in 3D printing, and exclusions from integration into electrical and plumbing systems. Total Kustom has experienced nozzle issues, while WASP (known especially for their total village concept with Shamballa), experienced problems with strength in parts.

ZP 151 powder and cement mortar were compared, with 3D printed parts being studied and evaluated in tensile and flexural strength tests. The researchers also compared mechanical behavior of the printed mortar with and without fiber for reinforcing the materials.

Particle size distributions for Z-printer powder, OPC, CAC and combination of CAC & OPC

Results of the strength test showed that samples increased in compressive strength as saturation levels increased.

'œThis is quite different from the results obtained by manual mixing of cement with water, which resulted in lower strength at a high w/c (saturation level) ratio,' stated Shakor.

Compressive strength of 3DP cubic samples with lithium carbonate.

For hand-mixed samples, lower water ratios allowed for better strength.

'œThe tests were applied at all saturation levels after the ratio of saturation levels was converted to the w/c ratio,' stated Shakor.

When saturation levels increased, the researchers also found that porosity decreased in the 3D printed specimens. The least amount of porosity was recorded at varying saturation levels of samples at S170-C340- LW.

Porosity of 3D printed samples.

'œThe mechanical behavior of the printed samples using glass fiber, such as the strain and ductility of the materials, showed improvement when loads applied on the printed sample. This study also discovered and presented the relationship between the end-effector velocity of the robot versus the slurry discharge and printed line width,' concluded the researchers.

'œUsing robotic arms in 3DP with fiber reinforcement offers an alternative option to the conventional methods of structural construction. In fact, it is an effective means to create structures possessing complicated geometries. This research also went some way towards understanding ideal concrete or mortar mix designs that are suitable, sustainable and environmentally friendly for such applications.'

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[Source / Images: '˜Investigation of Cementitious Materials and Fibre Reinforced Mortar in 3D Printing']

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