Method for recycling concrete
Initially, the concrete industry changed from using natural aggregates to crushed stone as aggregate. The next step may be to use recycled concrete as aggregate instead. This makes it more possible for the move towards circular production and economy.
Madumita Sadagopan, doctoral student at the University of Borås in Sweden, has in her research project investigated whether it is possible to produce structural concrete by replacing crushed stone and natural aggregate with recycled concrete without also increasing the amount of cement. She has now produced a new concrete with matching compressive strength and workability as a reference concrete.
Recycled concrete increases in value
"In Sweden, concrete waste is considered low-value; It simply ends up as landfill or is used in backfilling of roads and the construction of landfills. Concrete waste as aggregates in new concrete production extends the technical life of structural concrete and means closed-loop recycling. This is a high-utility application that preserves the value of the material," explained Madumita Sadagopan.
She studied what happens if conventional aggregates, such as crushed stone and natural aggregate, are replaced with 100 percent crushed concrete aggregate. In another scenario, fine natural aggregate was replaced with fine crushed concrete aggregate, with crushed stone retained as coarse aggregate. This represented about a 50% replacement of recycled aggregate. Part of the cement was also replaced with blast furnace slag. The purpose was to see whether it is possible to use this type of concrete for the design of structures and to investigate any differences when compared to concrete with natural or crushed stone aggregates. The result was a climate-optimised concrete.
"By introducing a mechanical pre-processing method to improve the quality of crushed concrete aggregates, and by replacing part of the cement with blast furnace slag from steel production, we managed to achieve a climate-optimised structural concrete. Moreover, we identified water absorption as a property that differentiated recycled concrete aggregate from virgin aggregates. By modifying a standard procedure to be more industrially feasible, we were able to arrive at a reliable result. These results were helpful in optimising the workability of the concrete, which is a critical requirement for industrial concrete."
How does your project benefit industry and society?
"Recycling of concrete means less concrete waste ending up at the landfill, and exhibits circular economy potential in the concrete production sector. The project demonstrates that recycled concrete is suitable as aggregate for an indoor reference concrete. Further research is required to solve practical aspects such as waste logistics and economic feasibility to develop a concrete-waste supply chain to commence the commercial recycling of concrete," said Madumita Sadagopan.
The project connects to the UN's global sustainability goals
"By using crushed concrete aggregates in place of virgin aggregates, we can reduce the excavation of virgin aggregates, which is necessary for drinking water reserves and ecological preservation," she explained.
The project connects to the global goal 15, Life on Land, and goal 12, Responsible Consumption and Production, and goal 11, Sustainable Cities and Communities.
Now, Madumita Sadagopan hopes for a transfer of knowledge of the researched methods to the industrial sector and a scaling up of the trials on an industrial level.
More information:
Recycling of concrete in new structural concrete. hb.diva-portal.org/smash/recor … sf?pid=diva2:1515177
Provided by University of Borås
