Effects of Biochar on the Properties of Alkali-Activated Materials Containing Construction and Demolition Waste

The effect of biochar in metakaolin alkali-activated materials (AAMs) modified with construction and demolition waste (CDW) is analyzed to investigate mechanical properties and provide a preliminary assessment of durability. A 30 wt% mix of brick and concrete powders replaced metakaolin. At the same time, biochar replaced metakaolin in different amounts, ranging from 0.5 to 5.0 wt%. The results show that, in samples containing CDW, a further replacement of metakaolin with biochar up to 1 wt% increases the compressive strength, both at short curing times (+20% after 7 days) and longer curing (+30% after 28 days) when compared to the CDW-modified sample without biochar. The dimensional stability of CDW-modified samples increases, and biochar addition provides a further benefit. Moreover, biochar addition below 1.5 wt% also reduces water absorption by capillary. Both features could forecast improved durability of the biochar-modified materials, to be validated with long-term experiments.