The pursuit to achieve carbon neutrality by 2050 has triggered the increase in bioenergy production, namely biomass combustion in fluidized bed boilers. However, this process generates bottom bed ashes (BBA), an inorganic solid waste that is commonly disposed of in landfills, a practice with a high economic and environmental impact. Thus, more sustainable management practices such as their use in the production of construction materials are being investigated. This work evaluated, the partial substitution of sand by two sorts of BBA (BBA_P and BBA_C generated in a power and a cogeneration plant, respectively) in a commercial screed mortar composition.
The BBA was characterized in terms of chemical composition (XRF), particle size distribution (by sieving), and morphology (SEM). Before its use, the wastes were sieved (0.1<Φ<1.2 mm) to match the used sands particle size range. The influence of the incorporation amount of BBA (25, and 50 wt.%) on the fresh (workability) and hardened state properties (bulk density, water absorption by capillary and immersion, flexural and compressive strength) of the screed mortar was evaluated.
These preliminary results showed that reusing up to 25 wt.% of both BBA understudy as an aggregate substitute, or up to 50 wt.% for BBA_P, allows producing a novel greener material with technological properties within the required parameters for its end use. In addition, the utilization of a commercial formulation facilitates the upscaling of the proposed valorisation solution.
  
Acknowledgments
This work was developed within the scope of the project CICECO - Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC).