Bottom ash from biomass combustion in BFB and its use in adhesive-mortars

• Bottom ashes from forest biomass combustion
• Non-hazardous waste
• Cementitious-adhesive

Bottom bed ash (BA) from forest biomass residue combustion generated in bubbling fluidized bed combustor (BFBC) was chemically, mineralogically and physically characterized and evaluated according to Decision 2003/33/CE and its landfill classification was determined based on criteria established by European and Portuguese legislations. Aiming to investigate its potential for being used as alternative aggregate in cementitious-adhesive mortar (CAM), formulations were produced by replacing commercial sand by an equivalent mass of 25, 50 and 100 wt.% of bottom ash. CAM properties were measured in fresh and hardened conditions. The bottom ash effect on the tensile adhesion strength (TAS) was investigated on samples cured under four distinct conditions. Macro and microstructural analyses were carried out to identify the influence of wetting capability and transference area in the TAS. Results revealed that high ash levels cause relevant changes in TAS, particularly those evaluated after 30 min of open time. However, within reasonable limits, the effects are minor and acceptable. This recycling route seems feasible, since it combines environmental benefits with economic advantages for the adhesive mortar producers in the sense that they can use BA as raw material, saving a natural resource; this recycling option is also important since one can avoid waste landfilling.