Recycled materials open new doors for 3D concrete printing

Recycled materials open new doors for 3D concrete printing

Research from RMIT shows that recycled glass and plastic combined with 3D printing technology can offer sustainable solutions for construction.

Over the past few years, 3D concrete printing (3DCP) has emerged as a potential game changer for the construction industry. This technology enables the fabrication of concrete structures via extrusion-based layer-to-layer deposition, instead of the conventional mould-casting method.

Studies have shown that 3DCP can have several advantages over the casting method, including allowing for complex geometry, less reliance on work labour, and improved manufacturing productivity.

However, both methods still require depletable raw materials like natural river sand.

Now researchers from RMIT University have developed a sustainable 3DCP process that replaces 50% of natural river sand with recycled glass, whose physical properties and chemical compositions are similar.

Concrete during a 3D printing process (pictured above) and concrete columns after printing (pictured below). Recycled materials open new doors for 3D concrete printing

The study published in the Construction and Building Materials journal investigated the effect of different grades of recycled glass (coarse versus fine) on the bending performance of 3DCP structures.

It found that cross-loaded 3DCP with an optimal concentration of coarse glass particles is a suitable and sustainable alternative for natural river sand.

As RMIT University PhD candidate and first author of the study Junli Liu explained, using recycled glass could make construction less dependent on sand – a natural resource currently undergoing issues of over-exploitation. Further, it would also help reduce the issue of waste glass taking up space in landfills.

In another study published in the Automation in Construction journal, researchers from RMIT University (Australia), HUTECH University (Vietnam) and the Indian Institute of Technology Guwahati proposed using recycled plastic to make concrete beams stronger.

They developed a new way to improve the bending strength and corrosion-related issues of concrete structures by reinforcing them with 3D printed plastic scaffolds. What’s even more special, the design is inspired by the structure of bones – a cellular structure that is naturally optimised.

RMIT STEM College Senior Lecturer Dr Jonathan Tran next to a 3D-printed concrete wall. RMIT STEM College Senior Lecturer Dr Jonathan Tran next to a 3D-printed concrete wall.

RMIT STEM College Senior Lecturer and lead author of the study Dr Jonathan (Phuong) Tran revealed that their plastic-reinforced concrete beam is four times stronger in load-bearing capacity, more durable, and more resistant to cracking than mould-casted specimens without any reinforcement.

He explained that concrete is a brittle material with inherent weakness in bending and stretching. Typically, it is required to be reinforced by steel rebars to overcome catastrophic failure and shatter without warning. However, steel reinforcement is heavy, expensive to produce and labour-intensive to install.

In contrast, the weight of plastic is around two and seven times lighter than those of concrete and steel materials, respectively. The plastic scaffolds don’t corrode and above all, plastic is a recyclable material and cheaper to produce.

According to Dr Tran, this reinforcing approach is “quite practical, sustainable, and scalable” thanks to the combination of 3D printing technology and the use of recycled plastic.

Dr Tran’s co-researcher and RMIT PhD candidate Nguyen Van Vuong added that bio-inspired reinforced concrete beams are also promising for a wide range of applications such as prefabricated complex structures, noise barrier wall panels, and concrete structures in seawater environments.

Empty plastic bottles Recycled plastic combined with 3D printing technology can offer sustainable solutions for construction.

Dr Tran believes that although 3D concrete printing is still a very new concept in Vietnam, it is never too soon for scientists and civil engineers to start exploring how it can support sustainable development.

According to the World Economic Forum in 2020, Vietnam produces around 3.7 million tonnes of plastic waste every year, only 10-15% of which is collected for recycling.

Meanwhile, shortage of sand for concrete production is a widespread issue across the country. The Ministry of Construction has estimated that legal supply of natural sand can only meet 40-50% of the demand of the construction industry.

“Plastic and glass waste is abundant in Vietnam. If it can be turned into useful construction materials in an innovative way using 3D printing technology, that would open new doors,” Dr Tran said.

Story: Ngoc Hoang

20 June 2022

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