Sustainably produced concrete mixtures from mineral residues and waste materials could partially replace Portland cement-based concrete in the future, especially in application environments prone to corrosion such as sewage systems, biowaste plants or tunnel drainage systems. Cyrill Grengg from the Institute of Applied Geosciences at Graz University of Technology (TU Graz) argues that it is not only an achievable goal, but also makes economic and ecological sense.
He heads the Christian Doppler Laboratory for waste-based geopolymer construction materials in the CO2-neutral circular economy, which officially opened on 8 March, and has eight corporate partners* involved in the project, who all seemingly see potential in the use of building rubble, slag, metallurgical gravel, mineral wool or ash to make more environmentally friendly and resistant concrete.
The project is working to a seven-year timeline of research – in conjunction with the participating firms – with funding from, among others, Austria’s Federal Ministry of Labour and Economic Affairs (BMAW). “The know-how researched here can be the basis for many other innovations,” commented Minister of Labour and Economic Affairs Martin Kocher.
Less consumption of cement and resources and less corrosion
Inorganic industrial secondary raw materials, such as slag and ash, as well as residual materials, such as mineral wool and clay-rich demolition materials, are processed in the CD lab and combined with carbon-rich waste materials, such as (waste) oils, biomass residues or organic fibres, depending on demand and intended use. The resulting geopolymer is an alternative to conventional Portland cement-based concrete. It offers comparable material properties, has better resistance to many types of corrosion and leads to less consumption of resources through recycling of previously landfilled residual and waste materials.
“Chemically, the geopolymer is something completely different from Portland cement, but the physical properties are very similar or even better in some cases,” says Grengg, who extolls the potential of geopolymers, especially in their much higher resistance to (bio)chemical corrosion. Portland cement is by far the most widely used binder in modern construction. However, it is susceptible to corrosion from wind, weather and other environmental influences, such as (bio-)chemically aggressive wastewater from sewage systems and sewage treatment plants. This leads to safety problems and high expenses for the maintenance of structures. Worldwide, costs caused by corrosion are estimated at 2.5 trillion US dollars (or approx. 3.4 percent of the global gross domestic product), large shares of which relate to concrete as a building material.
From landfill to recycling economy
At the same time, the production of building materials is responsible for about nine percent of all greenhouse gas emissions generated worldwide. And the current handling of residual and waste materials, for example from construction projects, still has great potential in terms of recyclability. Every year, 54 million tonnes of mineral waste are generated in Austria, which is 76 percent of the total waste volume. Of this, almost 60 percent is landfilled, resulting in the loss of valuable resources and large areas of land to landfill. “Today, large amounts of the residues and wastes used in the CD lab are landfilled, and only a small part is recycled. We want to take these materials away from landfills and integrate them into a CO2-neutral recycling economy,” says Grengg.
* The corporate partners in the project are Voestalpine Stahl Donawitz GmbH, Stahl- und Walzwerk Marienhütte GmbH, brantner green solutions GmbH, Initiative Ziegel, Research Association of the Stone and Ceramic Industry, CharLine GmbH, Kirchdorfer Fertigteilholding GmbH, MM-Kanal- Rohr- Sanierung GmbH and the Community of Styrian Wastewater Disposal Companies (including Linz AG and AWV Wiener Neustadt).