Given its status as the most widely-used manufactured material on Earth, reducing the huge environmental footprint of concrete would have significant consequences for the health of the planet. Researchers at the National University of Singapore (NUS) have put forward a new formula for stronger concrete that not only cuts a large amount of damaging materials from the equation, but makes use of upcycled waste clay at the same time.
In producing the more eco-friendly concrete, the NUS team started by taking aim at one of the primary ingredients in traditional forms of the material: sand.
This acts as the filler that combines with cement and water to give concrete its bulk and strength, but as our demand for concrete structures has grown in line with sprawling megacities and towering skyscrapers, so too has the demand for sand. A 2019 UN report revealed how increasing urbanization and infrastructure development has driven a three-fold increase in demand for sand over the last two decades, demonstrating how we are "spending our sand budget faster than we can produce it responsibly."
With little natural sand to speak of and urban development continuing apace, the team of scientists in Singapore experimented with ways it could be replaced in the concrete mix by an alternative, more sustainable material in the form of waste clay sourced from excavation sites around the city-state. The hope was to replace as much fine sand powder as possible, which is expensive, has a large carbon footprint and is a carcinogenic through prolonged exposure.
This clay is first heated to 700 °C (1,292 °F) which "activates" its bonding potential with the concrete. Through their experimentation, the scientists found this activated clay could be used to replace up to half of the fine sand powder usually used in concrete production. The finished product, which the team describes as ultra-high performance concrete, was not only greener, but featured much improved durability and could therefore be used to reduce the size of structural elements.
“Our discovery not only reduces the consumption of valuable resources but also promotes a circular economy with the utilization of waste clay," says Associate Professor Pang Sze Dai, who led the research. "It opens an avenue to transform this waste into a potential resource ... Globally, low-grade clay is abundant. Its multi-faceted utilization in concrete as fillers can not only help curtail the carbon footprint of concrete but also reduce the cost of concrete production."
As part of their future research, the scientists plan to investigate how other waste materials could also be used to replace concrete filler, and how locally-sourced sea sand could be used to replace imported river sand in Singapore.
The research was published in the Journal of Cleaner Production.
Source: National University of Singapore
