Concrete is one of the world’s most widely used building materials, forming the backbone of homes, bridges, tunnels and other important infrastructure.
However, making traditional concrete comes with a major environmental cost because its key ingredient, Portland cement, requires limestone and clay to be heated to around 1,400 degrees Celsius.
This energy-intensive process is responsible for about 7–8% of global carbon dioxide emissions.
Researchers at Kaunas University of Technology (KTU) in Lithuania believe there is a greener alternative.
Their latest study, published in Scientific Reports, shows that a new geopolymer mortar made entirely from industrial and construction waste could provide a more environmentally friendly building material while also offering excellent resistance to extreme heat.
Instead of using Portland cement, the researchers created a geopolymer binder from recycled ceramic brick waste collected from demolition sites and metakaolin waste from a Lithuanian glass factory.
Because the binder is activated using an alkaline solution rather than being produced in high-temperature kilns, it requires far less energy to manufacture.
The team also tested five different fine aggregates in the mixture, including sand, granite, basalt, ceramic waste and corundum. Their goal was to find which combination could best withstand intense heat while maintaining its strength.
The results were encouraging. After being exposed to temperatures of 800 degrees Celsius, the best-performing geopolymer mortars still achieved compressive strengths of up to 53 megapascals while showing only limited cracking. Conventional Portland cement concrete usually suffers severe damage and loses much of its strength after being exposed to similar temperatures.
According to Professor Danutė Vaičiukynienė from KTU’s Faculty of Civil Engineering and Architecture, this makes the new material particularly attractive for places where concrete must perform in very hot conditions. These include tunnels, industrial plants, chimneys, fireplaces, boilers, furnaces and chemical facilities, where structures need to remain stable even during prolonged exposure to high temperatures.
The researchers found that mortars containing corundum and ceramic waste performed better than the other mixtures after heat exposure. The study is among the first to directly compare several different fine aggregates within the same waste-based geopolymer system under identical high-temperature conditions.
One surprising discovery was that repeated heating did not weaken the new mortar. Instead, the material actually became stronger after multiple exposures to high temperatures. The researchers are continuing to study why this happens and whether the effect can be used to improve future building materials.
Beyond its fire resistance, the geopolymer mortar offers significant environmental benefits because it is made entirely from waste materials that would otherwise be discarded. The project also highlights how industrial by-products can be transformed into valuable construction materials instead of ending up in landfill.
Despite promising research from many groups around the world, geopolymers have not yet become common in the construction industry. Professor Vaičiukynienė says one of the biggest challenges is the lack of clear building standards and regulations for these materials. Established cement manufacturers and construction companies may also be hesitant to adopt unfamiliar products because of financial and legal concerns.
The KTU team plans to continue testing the mortar under a wider range of conditions while preparing a European patent application.
If future studies continue to deliver positive results, waste-based geopolymers could become an important building material that reduces carbon emissions while creating structures that are better able to withstand extreme heat and fire.
