Production of electricity / heat through the use of biomass is one of the possible ways to increase energy production from renewable energy sources and promote sustainable development by reducing direct greenhouse gas emissions chich is associated with the energy sector (Moraisi et al., 2011). In the coming years, biomass will have important role as a natural source of renewable energy, due to the rising cost of fossil fuels, highly questionable safety of nuclear energy and the need of carbon dioxide emissions reduction. (Callejón-Ferre et al., 2014). According to 2009/28/EC Directive about the promotion of use of energy from renewable sources, Biomass is defined as the biodegradable fraction of products, waste and residues from the agricultural industry (including also substances coming from plant and animals), forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste. Increasingly frequent use of alternative fuels, including biomass, in different areas of the industry cause a large production of new waste materials. Economic and environmental considerations are the cause of increased interest in the use of the economic potential of ash generated in these processes. In the article possibility of using new waste materials, which are fly ash from the combustion of mixed agricultural and forest biomass as hydraulic backfill material, solidifying and gobs caulking was analyzed.