Effect of biochar on the shrinkage deformation of ground granulated blast-furnace slag-cement mortars

This study was conducted to comprehensively analyse the potential role of different biochar as shrinkage-reducing agent for ground granulated blast-furnace slag-cement composites, including bamboo biochar (BB), waste wood biochar (WB), and rice husk biochar (RHB). Samples with 2 wt% BB (CBB2) exhibited the highest cement hydration, improving the 28-day compressive and flexural strength by 14.6 % and 7.7 % respectively. Due to its filler effects and internal curing, a 28-day shrinkage reduction of 16.8 % was found in CBB2 group when compared to the control. Meanwhile CBB2 achieved the lowest mass loss in dry environment exposure and apparent porosity at 28 days, exhibiting the highest electrical resistivity among all mortar groups. When the biochar dosage increased to 5 wt%, less improvement of the mechanical and durability properties was found. TG/DTG results indicated that CBB2 group had the highest content of bound water and portlandite, showing the effectiveness of fine BB in promoting cement hydration. Overall, this study recommended that up to 5 wt% fine-size biochar could be safely used as shrinkage-reducing agent in GGBF-cement composites.