Crushed Mining Waste Can Replace Cement

Mining waste can replace up to ten per cent of the cement used in concrete without compromising the strength of the materials.

waste management

Mountains of mining waste from all over the world are waiting to be resurrected as concrete construction material. New research at DTU Civil Engineering shows that up to 10 per cent of the cement in concrete can be replaced by mine tailings, which are the remnants of crushed ore after extraction of metals and substances.

The utilization of mine tailings can provide a significant contribution to reducing emissions of greenhouse gases from cement production, which accounts for five per cent of human emissions of CO2.

“We’ve performed physical and mineralogical analyses of mine tailings from mines in all parts of the world. The results show that a large selection of the samples have great potential to replace up to ten per cent of the cement used in concrete, while other mine tailings have properties which mean that they can only be used as filler,” says Pernille Erland Jensen, Associate Professor at DTU Civil Engineering.

Research into the use of mine tailings is supported by the Danish Construction Association, with consultant Anne Rosenskilde Lajer characterizing the project as highly relevant to the Danish construction industry, which needs new, innovative materials that can be used as additives in concrete.

Pernille Erland Jensen points out that the exploitation of mining waste is not only attractive because of the properties of the raw materials in concrete, but also because they can solve environmental problems from mining waste, and reduce CO2 emissions from cement production.

“Mine tailings are deposited in such quantities that this can make a real difference to the climate impact from the construction industry,”

Pernille Erland Jensen, associate professor at DTU Civil Engineering

“The interesting thing about these mine tailings is that they’re deposited in such quantities that if they’re used globally, this can make a real difference to the climate impact from the construction industry, because we reduce the amount of cement used when tailings can become a substitute in concrete production,” says Pernille Erland Jensen.

Mechanical tests of mine tailings from mines all over the world performed at DTU Civil Engineering have documented that a large share of the world’s mining waste can be used in concrete without compromising the strength of the concrete. But before mine tailings can be used, there is a need for more knowledge about the chemical properties of the materials and about whether they constitute an environmental pollution risk.

In a new study, Research Assistant Anne Mette Tholstrup Simonsen has studied the chemistry—in both the raw mine tailings and when the material is used in concrete. The studies were conducted on mine tailings from 13 different mines worldwide.

“Analyses show us whether we can recommend that some mine tailings are used unprocessed or whether they’re to be treated before they’re added to concrete. We’ve tested whether heavy metals will subsequently occur in too high concentrations, and whether they are leached out from concrete if it comes into contact with water. We’ve studied leaching from whole pieces of concrete and small grains—where we crush the concrete—so we know how concrete from a demolished building behaves if, for example, it is used as road fill,” says Anne Mette Tholstrup Simonsen.

The research is being conducted in new laboratories at DTU Civil Engineering and will form part of the EU project e.THROUGH, in which a number of companies and universities collaborate on utilization of mine tailings.

In addition, the researchers will include the results in a collaboration in DTU’s strategic partnership Nordic 5 Tech, where they can draw on the other Nordic countries’ long experience in mining industry. Finally, the researchers also bring the new knowledge to the partnership EIT Rawmaterials, which consists of 190 leading companies, universities, and research institutions from 20 countries in the EU.

Positive climate effect

Calculations from DTU Management show that it has a positive effect on CO2 emissions even if mining waste used as a cement substitute is transported over long distances. So much energy is consumed in cement production that you can transport one tonne of material by ship for a distance of approximately 20,000 km before this exceeds CO2 emissions from cement production.

The calculations are based on an average for ocean and ‘inland’ transport by sea. Without inland transport by sea, the figure is around 60,000 km.

Treatment of mining waste

Treatment of mining waste before it is used as a component in concrete can be performed using a number of methods such as electrochemical cleaning and electrochemical bath. Future development and analysis of various treatment methods are to clarify whether there are economic and environmental gains which make it attractive to utilize mining waste despite the processing required.

In addition, the researchers want to include even more different tailings in their analysis to support the statistical basis for their conclusions further.