Waste glass could lead to cheaper, lighter, stronger prefab concrete

Strong, lightweight and cheap prefabricated concrete panels for building construction could be on the horizon, and the key ingredient is a growing problem waste material: glass.

The recent Four Corners expose on the waste and recycling industry in Australia revealed literally mountains of waste glass being stockpiled in Victoria, thanks to falling resource prices that have made recycling uneconomic.

But a team from the University of Melbourne is onto a solution, finding that not only can waste glass replace dwindling sand resources in concrete (or other supplementary materials like fly ash and slag), the outcome is lightweight, stronger and cheaper than traditional concrete.

Project manager for the university’s recycled glass R&D project, Associate Professor Tuan Ngo, told The Fifth Estate that as the world ran out of sand, it was an obvious choice to target for replacement.

Beyond simply replacing sand with glass, the team has used chemical additives to make the resultant concrete lightweight and strong.

“Being lightweight is very important for prefab applications,” Dr Ngo said, including being easier to transport and work with.

There’s also a good cost basis.

“In terms of glass, it’s really cost-effective, as it is extremely cheap compared to sand,” he said.

He said the concrete could have applications in both commercial and residential settings.

Currently the project researchers are testing glass percentages from 10 per cent up to about 30 per cent, but there’s potential for greater percentages.

Researcher Dr Ali Kashani said the team was confident a high proportion of glass could be used, with the finest grades of ground glass delivering the greatest strength and durability.

“Our work has shown it has excellent sound, thermal insulation and fire-resistant characteristics,” he said.

“We are looking forward to working with the cement and concrete industries and building standard regulators to prove the viability of using these products in traditional concrete structures.”

Damian Crough, Associate Professor Tuan Ngo and Dr Ali Kashani in the lab with a block of glass-impregnated concrete.

Current codes present a hurdle

One hurdle is current standards and codes. Dr Ngo said while a certain percentage of concrete could contain replacement material, having large percentages would require an engineer to sign-off on it.

“But if you want to make it into an industry, we need amendments to concrete codes. We really want to get industry adoption.”

PrefabAus founding director and chair Damien Crough said upgrading building standards to allow more glass in concrete would “open doors”.

“This is where the real opportunities lie,” he said.

“Existing concrete supplementary materials like fly ash and slag are becoming harder to get and more expensive. The cost of glass will be an attractive factor for industry as it is readily available and inexpensive, being about a third of the cost of fine sand, or less.”

The project is being jointly funded by Sustainability Victoria and the Australian Packaging Covenant.

Sustainability Victoria acting chief executive Carl Muller said the organisation was funding a range of projects to find applications for waste streams. For example, another interesting project it is funding is at Victoria University, which is attempting to create structural beams made out of recycled plastics and waste glass for use under decking.

“This work can create jobs and, most importantly, ensure the community has confidence that recovered materials have a future use,” Mr Muller said.

The news also follows the release of a Beyond Zero Emissions roadmap on getting to a zero carbon cement industry in 10 years.

It also found that waste glass could be used as one of the raw materials for geopolymer cement, or even replace part of the need for sodium silicate activator.

“Australia produces about one million tonnes of glass waste every year, only about half of which is recycled back into glass,” the report said.

“The remaining half million tonnes is either used for low grade products such as road aggregate, or dumped in landfills. In Victoria alone there are stockpiles of 300,000 tonnes of waste glass. This waste glass is a problem as it is hard to recycle, and when reused it is largely driven by a need to find a way of disposing of waste glass rather than demand.”

Tyres also being investigated

Another research project Dr Ngo is working on, using separate grant funding from Tyre Stewardship Australia, is creating a lightweight, ductile concrete from recycled tyres.

Including recycled tyre crumb in concrete created a lightweight product but, importantly, created a product that had high levels of thermal and acoustic insulation.

Having good acoustics was particularly important, Dr Ngo said, as lightweight products, such as cross-laminated timber, tended to have poorer acoustic properties.

However, this project found that adding recycled tyres could reduce weight while actually increasing acoustic insulation. Possible uses could be in residential buildings, intertenancy walls, auditoriums, offices, plant rooms and hospitals.

Dr Ngo is hopeful that Australia can make an export industry based upon high-performance construction products including recycled materials.

“The next generation of prefabricated structures can benefit from Australia’s eco-friendly, prefabricated housing research which is striving to deliver breakthrough products to enable our housing industry to compete on a global stage,” Dr Ngo said.

Crough agrees.

“The opportunities for a wide range of projects, and the environment, is enormous.”

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