Waste-based geopolymer mortar offers greener, fire-resistant alternative to concrete

The construction industry is actively seeking sustainable and fire-resistant alternatives to traditional concrete, driven by the significant CO₂ emissions associated with Portland cement production and the demands of rapid urbanization. Portland cement manufacturing, which involves heating limestone and clay to high temperatures, accounts for approximately 7-8% of global CO₂ emissions.

Researchers at Kaunas University of Technology (KTU) have been investigating waste-based geopolymer binders as a solution. Their recent study utilized ceramic brick and metakaolin waste as precursors, combined with five different fine aggregates: sand, granite, basalt, ceramic waste, and corundum. This geopolymer mortar offers a lower-temperature production method and can be made entirely from waste materials, unlike the resource-intensive and high-temperature process for Portland cement.

The developed geopolymer mixes exhibited remarkable performance under high temperatures. The best-performing formulations achieved compressive strengths of 34.7 MPa and 53.0 MPa at 800°C, with minimal microcracking. In contrast, conventional Portland cement concretes typically experience significant strength loss and damage at similar temperatures, making the waste-based geopolymers a more robust option for structures exposed to fire.

Professor Danutė Vaičiukynienė from KTU highlighted the material's suitability for areas near heat sources, such as chimneys, boilers, and tunnels, where retaining strength after extreme heat exposure is critical. The research identified corundum and ceramic waste aggregates as providing the best strength retention after 800°C exposure. Notably, repeated exposure to high temperatures did not weaken the mortar; instead, it became stronger.

The environmental benefits are substantial, as the geopolymer binder is produced entirely from waste materials, including milled ceramic brick waste from demolition sites and kaolin waste from a glass factory. Unlike Portland cement, geopolymer binders are activated by alkali without requiring excessive temperatures, further enhancing their eco-friendliness. Despite these advantages, widespread adoption in construction is slow, partly due to a lack of clear standards and regulations, alongside psychological and economic barriers from the established cement industry.