Improving circularity of biomass ash: a theoretical, experimental, and modelling approach to find sustainable solutions for application in cement or soil

Currently it is normal practice to landfill biomass ash. As an alternative, biomass ash has been proposed as a substitute for raw clinker materials, a secondary cementitious material, or as a soil amendment. This alternative use of biomass ash avoids landfilling, saves traditional resources for cement production, and hence lowers the carbon footprint of cement products.

This thesis has shown that biomass ash can be successfully used as raw material for clinker production and substitute a large part of the raw feed minerals. The direct use of biomass ash as secondary cementitious material was also found to be feasible for specific biomass ash types. The inclusion of biomass ash at 20 and 40% by weight of Portland cement reduced the compressive strength after 28 days but a functional strength was still obtained.

Results also showed that an assessment and regulatory criteria based on the leaching rather than total content of elements may widen the application of biomass ash as soil amendment. When biomass ash was mixed in cement, the cement matrix dominated the release of elements in leaching tests.

Results from the life cycle assessment established that biomass ash use in cement is always a more sustainable solution than landfilling. The environmental performance of biomass ash blended with cement was equal to that of traditional cement during all the considered life stages of materials