Bottom ash is formed by incinerating non-hazardous waste at high temperatures of around 1000 °C and is a solid, porous, stone-like material.
At the end of the waste incineration process, the resulting bottom ash can be used for road construction, building foundations, the production of paving blocks, covering waste layers in landfills, landfill closure, and the construction of temporary roads on landfill sites, subject to meeting applicable environmental criteria.
Each year, Gren processes non-recyclable waste to recover energy for homes and businesses. About 25% of this waste becomes bottom ash, which Gren prepares for reuse instead of disposal, supporting the reuse of a waste by-product in construction materials.
Between 2021 and 2025, Gren has reused approximately 257,000 tonnes of bottom ash, equivalent to nearly 1 million tonnes of waste. What once would have gone to landfill is now used in the foundation of roads, bike paths, and industrial sites in Lithuania.
Through research, innovation, and partnership, Gren is putting bottom ash reuse into practice in infrastructure projects in Lithuania.
Reusing bottom ash delivers the following measured benefits:
Gren’s bottom ash complies with strict environmental criteria: metal content ≤5%, organic carbon ≤3%, ignition loss ≤6%, and controlled leaching values. Before reuse, the material is conditioned for approximately three months to ensure stability and environmental safety.
Gren’s bottom ash has been successfully used in multiple infrastructure projects, including:
These projects demonstrate how bottom ash can replace imported natural aggregates in specific applications.
In 2021, a unique road section was built in the Jurbarkas district where bottom ash generated from waste-to-energy processing of non‑hazardous waste was used. This was the first project of its kind in Lithuania, aimed at conducting a comprehensive study of the road and determining the impact of bottom ash on road performance during operation. In the one‑kilometre-long test section, 9,000 tonnes of bottom ash were used. The bottom ash was produced at the waste‑to‑energy plant of UAB Gren Klaipėda and prepared for use.
In 2025, a bicycle and pedestrian path was constructed on Sausio 15‑osios Street in Klaipėda using bottom ash generated by Gren Klaipėda. During the works, nearly half a kilometre of the section from the intersection with Taikos Avenue to Tilžės Street was renovated. A bicycle path with a red asphalt surface and a pedestrian walkway paved with grey paving stones were installed.
Gren collaborates closely with the VILNIUS TECH Road Research Institute, whose studies have confirmed that bottom ash meets all environmental and engineering requirements for use in unbound road base layers.
This innovation was recognised with the 2024 Baltic Road Award for Scientific Innovation, acknowledging Lithuania’s leadership in applying circular economy principles to road engineering.
The awards are presented during the International Baltic Road Conference, which takes place every four years in one of the Baltic countries.
Explore how Gren transforms waste into energy that supports local communities and reduces landfill.
