Work

Microstructural and pore network evolution of biochar-modified alkali-activated slag cement

Year: 2025

Type: article

Abstract: The urgent need for decarbonising construction materials aligns with global efforts to achieve carbon neutrality. This study explores the potential of biochar as a carbon sink in clinker-free alkali-activated slag (AAS) systems, offering a pathway to significantly reduce carbon emissions. By incorporating biochar into AAS, the microstructural impacts were investigated using advanced characterisation techniques. The findings reveal that biochar inclusion does not alter the primary hydration products of AAS, except for the introduction of calcite. Enhanced crystallinity and structural regularity were observed in the layered double hydroxides (LDH) and C-A-S-H(I) phases, as evidenced by sharper diffraction peaks. However, the addition of 25% biochar significantly increases permeability, indicating higher pore heterogeneity, which could promote gas diffusion. At the interfacial transition zone (ITZ), a ‘wall effect’ leads to small slag particle aggregation and enhanced slag hydration, yet weak bonding between biochar and AAS paste results in ∼2 μm gaps. The chemical composition of the ITZ closely resembles the inner product (IP) of slag, highlighting the influence of particle interactions in this region. These findings offer valuable knowledge for optimising the use of biochar for carbon-negative construction materials, potentially leading to more environmentally friendly and carbon-efficient construction practices.

Source: Journal of Building Engineering

DOI: 10.1016/j.jobe.2025.114584