/ 2 July 2021

Using ‘rubbish’ instead of stone makes concrete greener

A Palestinian Man Working In A Factory That Recycles Rubble
The University of the Free State’s green project aims to curb environmental impact of concrete by using industrial waste and by-products. (Photo by Ahmed Zakot/SOPA Images/LightRocket via Getty Images)

A new green project study at the University of the Free State (UFS) intends to unearth new ways to produce concrete, in an attempt to curb the impacts of the conventional ways of producing this composite material on the environment. 

According to various studies, and to the lead engineer of the UFS project, cement production worldwide is responsible for about 5-6% of overall carbon emissions. 

Green concrete is a construction material that can be used as an alternative to conventional concrete, and it could also provide governments with economic benefits by using recyclable waste materials that will minimise energy consumption. 

“Generally, conventional concrete is made by mixing ingredients comprising Portland cement, sand, stone, and water. All these ingredients are obtained from natural resources. The use of these limited and irreplaceable natural resources leads to substantial damage to nature,” says the lead engineer on the UFS study, Dr Abdolhossein Naghizadeh. 

He told the Mail & Guardian that the processes that take place to prepare the raw materials resulted in severe impacts on the environment, whereas in green concrete technology, the natural raw materials were replaced with industrial waste or by-products. “For example, fly ash (residual material from coal burning in power plants) is used instead of cement, while crushed waste glass or recycled concrete is used as the aggregates (particulate matter) instead of natural sand and stone.”

“The major impact of conventional concrete on the environment is related to the chemical reactions that take place in the production of Portland cement (this is cement used for concrete and mortar production), known as calcination. During the calcination process that occurs at elevated temperatures (about 1 300°C), a significant amount of carbon dioxide is released into the atmosphere,” said Naghizadeh. 

The production process for making cement also causes dust pollution, which can impact air quality. As a result, its use in many human-made materials and structures is under scrutiny.

A study in the scientific journal Nature has found that the demand for cement and concrete is set to increase over the next 50 to 100 years, so finding ways of greening the process and the product are important.  

“Reductions in carbon dioxide emissions are possible through the introduction of improvements across the cement and concrete value chain. Research and development are urgently needed to allow post-2050 construction to meet future emissions-reduction targets,” that study says. 

The initial stages of the green concrete project are already completed, and the endeavour is set to be finished within the next two years.  “The basic material has been formulated, and a mixed design approach based on the available South African industrial waste materials has been developed. At the current stage, we are working on the optimisation of the mixtures to produce a more economical and user-friendly product,” he said. 

While the project at this stage did not include the input of environmental organisations, Naghizadeh said it was hoped that such collaborations, as well as with partners from the cement and construction industries, would take place in the future. 

Chris Gilili is an  Adamela Trust climate and economic justice reporting fellow, funded by the Open Society Foundation for South Africa