SINGAPORE: Concrete – one of the most consumed materials in the world – can be made significantly more environmentally friendly and thrice as durable with the use of waste clay, as a team of engineers from the National University of Singapore (NUS) has found.
The discovery entails using clay from excavation and construction works, which would have otherwise been junked, to replace up to half the sand or cement needed to make concrete.
The process can tackle several issues, such as concrete’s hefty carbon footprint.
For instance, the cement industry alone was responsible for about 8 per cent of the world’s carbon dioxide emissions in 2018, according to think tank Chatham House.
It would also upcycle waste, ease pressures on landfills, and create a new resource to feed Singapore’s continued need for concrete, the team said.
They added that it is the first project in the world to have used marine clay – the type of clay found in Southeast Asia – to make concrete.
HOW IT WORKS AND WHY IT MATTERS
Excavated waste clay is collected from construction sites, then dried and ground up. After that, it is heated to change some of its properties.
It can then be used to replace up to 50 per cent of the aggregates typically used in concrete, depending on the grade of the mixture that is needed.
“By reducing this amount of (cement and sand), we are lowering the embodied carbon in construction materials … by also about 50 per cent,” said Associate Professor Pang Sze Dai, who led the research team from the civil and environmental engineering department.
The process can produce ultra-high performance concrete for buildings, to low-performance ones for roadside curbs, for instance.
The solution would also upcycle massive amounts of clay generated from tunneling and foundation works, which are common in Singapore, he said.
That deals with the issue of disposing this clay – a welcome prospect given that the country’s first and only landfill, Pulau Semakau, is set to be fully filled by 2035.
In addition, the discovery could feed Singapore’s need for construction materials in urban development.
“Through this research … it’s trying to look at tackling this landfill space and also creating our own resource from the waste. So I’d say it’s sort of killing two birds with one stone,” said Assoc Prof Pang.
The end-product would also be more three times more durable, as waste products densify the material and make it less porous, said Assoc Prof Pang.
This would be useful in a humid country like Singapore, where materials deteriorate faster compared to temperate countries, he noted.
From a cost-perspective, Assoc Prof Pang said producing this concrete “will not be more expensive than what we currently have”, and costs could go down further if processes are scaled up.
In addition, there will be cost savings from not needing to dispose of the waste clay.
“In terms of waste materials, there's a gate fee, which is for incineration. There's also a landfill fee, and these two numbers are going up. And through these two numbers, we can have substantial savings from there.”
The team said that its new concrete measures up to existing performance requirements.
It has also been working with government agencies, such as the Building and Construction Authority and JTC Corporation, to look at the potential of using the concrete safely for construction.
They are also working with a builder and developer to pilot using the concrete in upcoming projects – which they hope will happen in one to two years.
This would make other industry players more receptive to the material, Assoc Prof Pang said.
In the meantime, they are eyeing other types of waste – such as municipal solid waste ash which come in “huge amounts” and cannot by recycled, he added.
Apart from upcycling this, they are also studying how waste can be used to capture carbon.
Assoc Prof Pang said: “Our waste in Singapore is actually a resource, so it's just how we can (extract) value.”